Luminous Landscape Forum
Site & Board Matters => About This Site => Topic started by: ErikKaffehr on July 31, 2011, 04:16:53 pm
-
Hi,
Agree with the conclusion, we should to expose to the right and the cameras should support this.
On the other hand I´d say that Michaels explanation of why we should expose to the right is lacking. The reason to expose to the right is mainly that we want maximize signal (which is the number of photons detected). There is no simpler explanation, and it also happens to be the correct one.
Best regards
Erik
-
Eric,
Saying "maximize signal" isn't terribly useful unless you also explain why. Not everyone (in fact not that many) has the technical understanding needed for that simple phrase to make sense.
Which is why I wrote the article.
Michael
-
ETTR is right and good. The gotcha is the differential clipping of highlights as mentioned, which does make it a touch tricky, but certainly computable in a live-view situation. Although lack of code values in deepest shadows is an issue, the major problem is sensor read noise, and the brighter the signal, the less contribution read noise makes to the image. That exactly fits in with Erik's explanation.
Graeme
-
Michael,
The real issue I have with your article that you imply that noise would depend on the number of tonal steps in the dark areas, this is however not generally the case. Noise is coming from different factors, the obvious ones being shot noise (the natural variation of photons) and readout noise. Shot noise is as pointed out in your article proportional to the square root of the captured photons, while readout noise is fixed.
In general we talk about signal, which is essentially the light we detect, and noise which is the unwanted variation in sensor signal. We normally want to maximize signal/noise. If we look at shot noise we know that noise is the square root of the signal, so SNR (Signal Noise Ratio) is also the square root of the signal.
Let's assume that a sensor cell detects 10000 photons. The square root of 10000 is 100 so our SNR would be 100. Would we expose two stops less, the number of photons would be 2500 and SNR would be 50 (which is still very good).
If we assume that darks are three stops below midtones, and that midtones are at 10000 photons when correctly exposed to the right, SNR would be like sqrt(10000/8). With two stops less exposure we would have sqrt(2500/8) = 17.6.
When we reduce exposure further we need also to take readout noise into account which can be something like 10 electrons. This would add up with the shot noise. This addition would be in quadrature so for two step underexposed (relative to ETTR) and three stops under midtones we would have:
Shot noise = 17.6
Readout noise = 10
Noise = sqrt(17.6^2 + 10^2) -> 20.3
Now, a 12 bit converter would see 4096 different values, if we assume that saturation is about 50000 photons the lowest bit would correspond to about 12 photons, while the variation on the number of photons would be around 20. This pretty much also illustrates that there is little practical value in 16 bit converters. Let's assume that we have a new device from Phase Zero, totally devoid of readout noise and having pixels holding maximum 50000 electrons. If we assume 14 bit conversion we would have 16384 steps. Each step would correspond to 3 electrons. With no readout noise SNR would be 1.7, except that Poisson statistics would not be valid for three electrons. There would be little difference in doing 16 bit conversion or 14 bit conversion, and multiplying the signal by four and adding 2 random bits!
Best regards
Erik
Eric,
Saying "maximize signal" isn't terribly useful unless you also explain why. Not everyone (in fact not that many) has the technical understanding needed for that simple phrase to make sense.
Which is why I wrote the article.
Michael
-
The reason to expose to the right is mainly that we want maximize signal (which is the number of photons detected).
More photons = better signal...underexposing to "preserve" highlight detail is a bad practice as there is a ton of info in the brightest stop if you know how to tease the data out. Clearly, when shooting a high dynamic range scene, you must take care to avoid clipping important textural detail. On the other hand the tools we currently have (flashy highlight warnings suck) really don address the issue.
The bottom line I would say is to take a neg shooter's point of view; shoot for the shadows, develop for the highlights. With so much data in those brightest areas, it really ain't that hard. See ETTR (http://schewephoto.com/ETTR/) and look at the Niagara Falls image to see just how much detail there is in the uper portion of the capture/
-
In general we talk about signal, which is essentially the light we detect, and noise which is the unwanted variation in sensor signal. We normally want to maximize signal/noise. If we look at shot noise we know that noise is the square root of the signal, so SNR (Signal Noise Ratio) is also the square root of the signal.
Erik,
You might wanna dial down the math just a bit...(pretty sure Mike doesn't really care about that stuff). The main take away from Mike's article is that if you are shooting a low contrast scene, using your exposure meter and centering the image data in the center of the histo is a suboptimal idea...move the exposure to the right (to capture more photons and hence get a better capture). It's better to tone your curve down (darken) than it is to adjust digital captures to be lighter. Agreed? More photons=less noise?
-
What if you are shooting handheld in low light, does ETTR still make sense? Does ETTR only make sense at the lowest possible ISO setting? Should one trade ISO for speed in order to ETTR when conditions require it?
I regularly shoot handheld very low dynamic range scene in low light where all the data falls within one stop. There are now essentially 4 variables in play to achieve an acceptable exposure: timing, aperture, ISO, and 'amount of ETTR'.
For instance, here are few possible exposure choices at a given aperture:
ISO 400 1/200 no-ETTR
ISO 1600 1/200 max-ETTR
ISO 400 1/50 max-ETTR
ISO 100 1/50 no-ETTR
Which is best?
-
Jeff,
Sorry for the math...
Absolutely agreed, more photons = less visible noise! Incidentally, this is also one of the reasons that larger sensors yield better image quality. A larger sensor collect more photons!
Best regards
Erik
Erik,
You might wanna dial down the math just a bit...(pretty sure Mike doesn't really care about that stuff). The main take away from Mike's article is that if you are shooting a low contrast scene, using your exposure meter and centering the image data in the center of the histo is a suboptimal idea...move the exposure to the right (to capture more photons and hence get a better capture). It's better to tone your curve down (darken) than it is to adjust digital captures to be lighter. Agreed? More photons=less noise?
-
Hi,
This may depend a bit on what you are shooting! Canon's and some Nikons have different characteristics from newer Nikons using Sony based sensors. With Canon and Nikon D3S and D700 you would probably increase ISO to reduce noise (perhaps up to 1000-1600). On recent Sony sensors it may have less significance, Nikon D3X, D7000. Pentax K5 and Sony Alpha 580 seem to be "ISO-less" cameras. You always want to collect as many photons as possible.
So advice is: On Canon increase ISO and expose to the right. On cameras with Sony sensors it may matter little.
Best regards
Erik
What if you are shooting handheld in low light, does ETTR still make sense? Does ETTR only make sense at the lowest possible ISO setting? Should one trade ISO for speed in order to ETTR when conditions require it?
I regularly shoot handheld very low dynamic range scene in low light where all the data falls within one stop. There are now essentially 4 variables in play to achieve an acceptable exposure: timing, aperture, ISO, and 'amount of ETTR'.
For instance, here are few possible exposure choices at a given aperture:
ISO 400 1/200 no-ETTR
ISO 1600 1/200 max-ETTR
ISO 400 1/50 max-ETTR
ISO 100 1/50 no-ETTR
Which is best?
-
Hi,
Agree with the conclusion, we should to expose to the right and the cameras should support this.
On the other hand I´d say that Michaels explanation of why we should expose to the right is lacking. The reason to expose to the right is mainly that we want maximize signal (which is the number of photons detected). There is no simpler explanation, and it also happens to be the correct one.
Best regards
Erik
Eric,
You are exactly correct! The brightest f/stop of a digital exposure on current 12 bit sensors has nowhere near 2048 levels because of the presence of noise. Most of those 2048 levels are wasted in encoding noise. Furthermore, because of the Weber-Fechner law (see Norman Koren's Human Vision and Tonal Levels (http://www.normankoren.com/digital_tonality.html)) the eye can appreciate only about 70 levels in the brighter f/stops and even fewer in the darker ones. However, extra levels are useful if you are doing an extreme amount of editing of the tone curve.
As you correctly state, we expose right to get a higher signal to noise value as explained in depth by Emil Martinec (http://theory.uchicago.edu/~ejm/pix/20d/tests/noise/noise-p3.html#ETTR), who expressly discusses the fallacy of Micheal's original ETTR article. These concepts have been discussed at length on LULA and the Adobe forums and even Jeff Schewe has abandoned the levels argument and I was very discouraged to see Michael sticking to his original reasoning. The main improvement with ETTR is in the shadows, not the highlights.
As Emil discusses in his article, the Nikon compressed NEF format is visually lossless because it throws away redundant information in the brighter f/stops.
Regards,
Bill
-
There is someone besides the camera makers that need to get on board with this, the RAW converter makers.
ACR/LR causes ETTR problems with some camera profiles. Unfortunately ETTR and then moving the exposure control doesn't actually work with all camera profiles because some place a color "twist" prior to the exposure compensation. As a result you *will* get color errors when doing ETTR with such a profile. If, on the other hand, the twist is applied post EC then everything is OK.
There doesn't seem to be a lot of rhyme or reason as to which camera profiles do it which way and from the discussions I've seen on the Adobe forums so far the response from Adobe has a been a bit obtuse on the issue.
At least with ACR/LR the problem is resolvable if you create your own profile with no pre-EC twists. I don't know about other converters...
Ken
P.S. Nice article. I completely agree we need some more intelligent digital exposure tools in our cameras. True RAW histograms desired as well! Thanks for revisiting an interesting and important topic.
P.P.S. As a signal processing engineer I find the "levels" rationalization at the start of the article a red herring. Maybe it is an analogy that is helpful for some people to be motivated to ETTR, but it is in fact not at all relevant to ETTR. The noise discussions later in the article are what are relevant to ETTR. There are no cameras on the market in which quantization levels play any role in image noise, read noise and shot noise dominate in all of them.
-
There is someone besides the camera makers that need to get on board with this, the RAW converter makers.
ACR/LR causes ETTR problems with some camera profiles. Unfortunately ETTR and then moving the exposure control doesn't actually work with all camera profiles because some place a color "twist" prior to the exposure compensation. As a result you *will* get color errors when doing ETTR with such a profile. If, on the other hand, the twist is applied post EC then everything is OK.
There doesn't seem to be a lot of rhyme or reason as to which camera profiles do it which way and from the discussions I've seen on the Adobe forums so far the response from Adobe has a been a bit obtuse on the issue.
At least with ACR/LR the problem is resolvable if you create your own profile with no pre-EC twists. I don't know about other converters...
Ken
P.S. Nice article. I completely agree we need some more intelligent digital exposure tools in our cameras. True RAW histograms desired as well! Thanks for revisiting an interesting and important topic.
P.P.S. As a signal processing engineer I find the "levels" rationalization at the start of the article a red herring. Maybe it is an analogy that is helpful for some people to be motivated to ETTR, but it is in fact not at all relevant to ETTR. The noise discussions later in the article are what are relevant to ETTR. There are no cameras on the market in which quantization levels play any role in image noise, read noise and shot noise dominate in all of them.
Ken,
A great post! You may be a newbe to this forum, but obviously not to the realm of digital processing. Your point concerning hue twists is an important one and it is my understanding that with ACR the twists are often applied after exposure, or else no one would be reporting serious problems with them.
Regards,
Bill
-
If ETTR were to be the way in which your camera took a picture, what do you want to see when reviewing on the LCD? The picture as taken or the picture as taken with exposure correction applied?
Next, which one of those do you put in the thumbnail of the raw file?
And what if you want different output for each?
For example, when I'm shooting, I want to see if I've blown highlights (and where they are) when I review on an LCD but if I'm browsing through pictures with Windows Explorer, having thumbnail pictures that are all ETTR'd is not terribly useful. It also doesn't play well with software such as DLNA servers that will "serve" a raw picture file by extracting the JPEG.
I don't believe that ETTR will ever default to "ON" in any consumer grade camera because either the shutter speed is going to be slower (greater chance of blurry pic) or the ISO increased to keep the shutter speed down and both will negatively impact the picture quality of the average photographer that doesn't whip out their tripod for each and every shot.
-
Hi,
I have the impression that Michael suggested a setting for ETTR. Would we have a setting for ETTR we would not really need to care about blown out highlights, because the camera would never overexpose non specular highlights.
There are some practical issues with automating ETTR exposure. To start with I would like to have histogram calculated from RAW pre color balance.
Best regards
Erik
If ETTR were to be the way in which your camera took a picture, what do you want to see when reviewing on the LCD? The picture as taken or the picture as taken with exposure correction applied?
Next, which one of those do you put in the thumbnail of the raw file?
And what if you want different output for each?
For example, when I'm shooting, I want to see if I've blown highlights (and where they are) when I review on an LCD but if I'm browsing through pictures with Windows Explorer, having thumbnail pictures that are all ETTR'd is not terribly useful. It also doesn't play well with software such as DLNA servers that will "serve" a raw picture file by extracting the JPEG.
I don't believe that ETTR will ever default to "ON" in any consumer grade camera because either the shutter speed is going to be slower (greater chance of blurry pic) or the ISO increased to keep the shutter speed down and both will negatively impact the picture quality of the average photographer that doesn't whip out their tripod for each and every shot.
-
There are some practical issues with automating ETTR exposure. To start with I would like to have histogram calculated from RAW pre color balance.
Is there a reason why we can't have that now?
What I mean to say is that it is not very easy to map the histogram to what you see very easily by looking at the histogram for each of the RGB colour channels so why pretend that we can look at it and map it (in our heads) to what we see in the picture?
-
Hi!
I don't see why we won't have raw based histograms. As far as I can recall the Leica S2 has raw based histograms but most other cameras have histograms calculated from JPEG. >Don't know why!
Best regards
Erik
Is there a reason why we can't have that now?
What I mean to say is that it is not very easy to map the histogram to what you see very easily by looking at the histogram for each of the RGB colour channels so why pretend that we can look at it and map it (in our heads) to what we see in the picture?
-
See ETTR (http://schewephoto.com/ETTR/) and look at the Niagara Falls image to see just how much detail there is in the uper portion of the capture/
Jeff,
The amount of recovery in your Niagra Falls shot is astounding, but the raw file is not nearly so clipped as the ACR histogram would suggest, likely because of the BaselineOffset that ACR uses for your camera. Since I have your latest ACR book, I was able to download the raw file. The ACR histogram with camera default settings is shown below along with the raw histogram as shown by Rawnalyze. Before white balance, the red channel is entirely intact and the green and blue channels, while clipped, contain considerable data. I'm not so sure that the number of levels in the brightest stop has much to do with the recovery.
Regards,
Bill
-
It always amazes / annoys / amuses me when I publish an article that has been painstaking peer-reviewed by some of the brightest minds in the industry – people who design sensors and write raw software (in this instances) and then "experts" whose credentials are unknown tell me (us) why the information in the article is wrong.
This was the case with my original ETTR article. I think I trust Thomas Knoll's knowledge of digital imaging (the original author of Photoshop and Camera Raw) over some online commentator.
Similarly in this instances. I'm sure that there are areas to quibble over (both scientists and artists love to quibble). But when it comes to arcania and subtleties in complex topics I'll continue to trust known experts whose bona fides are well established.
Michael
-
I don't believe that ETTR will ever default to "ON" in any consumer grade camera because either the shutter speed is going to be slower (greater chance of blurry pic) or the ISO increased to keep the shutter speed down and both will negatively impact the picture quality of the average photographer that doesn't whip out their tripod for each and every shot.
With the latest cameras such as the Nikon D7000, it is the exposure on the image plane (lux seconds) that determines the image quality (SNR) and not the appearance of the histogram on the camera preview. Increasing the ISO will make the histogram appear more to the right and give a brighter preview, but increasing exposure in the raw converter will give the same results as a low ISO with a high shutter speed or large aperture, as long as the number of photons collected (the exposure) remains the same.
Regards,
Bill
-
It always amazes / annoys / amuses me when I publish an article that has been painstaking peer-reviewed by some of the brightest minds in the industry – people who design sensors and write raw software (in this instances) and then "experts" whose credentials are unknown tell me (us) why the information in the article is wrong.
This was the case with my original ETTR article. I think I trust Thomas Knoll's knowledge of digital imaging (the original author of Photoshop and Camera Raw) over some online commentator.
I think that it was one of those rare occasions where Mr. Knoll misspoke when the made the comment that the brightest f/stop of a 12 bit capture contains 2048 discrete levels--he did not consider noise. Emil Martinec has a PhD in physics and is a full professor at the University of Chicago. His analysis is beyond refutation. Did you take the trouble to read it?
DXO (http://www.dxomark.com/index.php/About/Glossary/Q-R-S-T/Tonal-range) gives the screen tonal range of the P65+ at 8.64 bits. That is the number of bits necessary to encode the number of discrete levels that the camera can detect. 2^8.64 = 399, which is far short of the theoretical number of levels in a 14 or 16 bit linearly encoded raw file.
In science, reason and data trump expert opinion. We no longer bleed patients for croup. That is how the "expert" physicians killed George Washington.
Regards,
Bill
-
I have the impression that Michael suggested a setting for ETTR. Would we have a setting for ETTR we would not really need to care about blown out highlights, because the camera would never overexpose non specular highlights.
There are some practical issues with automating ETTR exposure. To start with I would like to have histogram calculated from RAW pre color balance.
Olympus has ETTR (http://www.luminous-landscape.com/forum/index.php?topic=46071.0) in some (all?) of their FT/MFT cameras, perhaps compacts. Guillermo Luijk posts some reservations about its utility later in the thread.
-
What if you are shooting handheld in low light, does ETTR still make sense? Does ETTR only make sense at the lowest possible ISO setting? Should one trade ISO for speed in order to ETTR when conditions require it?
I regularly shoot handheld very low dynamic range scene in low light where all the data falls within one stop. There are now essentially 4 variables in play to achieve an acceptable exposure: timing, aperture, ISO, and 'amount of ETTR'.
For instance, here are few possible exposure choices at a given aperture:
ISO 400 1/200 no-ETTR
ISO 1600 1/200 max-ETTR
ISO 400 1/50 max-ETTR
ISO 100 1/50 no-ETTR
Which is best?
That depends on the read noise of the sensor and the camera electronics. For a detailed discussion, see Emil Martinec (http://theory.uchicago.edu/~ejm/pix/20d/tests/noise/noise-p3a.html). For older cameras such as the Nikon D3, read noise improves until about ISO 800. Beyond that point, one can leave the camera at ISO 800 and increase exposure in the raw converter. For newer cameras such as the Nikon D7000 and the Pentax equivalent, the results would be very similar regardless of the ISO as long as total exposure is the same. Raising the ISO does limit highlight headroom. With the D7000 you could leave the ISO at base and give as much exposure as f/stop and shutter speed considerations allow, and make up the rest in the raw converter.
The above discussion assumes that total exposure is the same (EV value determined by the f/stop and shutter speed). You don't give the aperture, but I assume that it is the same in the first and last two comparisons.
Regards,
Bill
-
Camera profiles in ACR/LR with lightness-dependent color should not have issues with ETTR, as long as you perform the "normalization" using the Exposure slider, rather than the Brightness slider. For example, if I expose an extra 1.5 stops in the field (relative to how bright I want the actual image to be), then in ACR I would compensate with Exposure -1.5.
Eric
-
It seems to me that Michael is giving us the recipe for a metaphorical pie, while the engineers are telling us how to make flour and grow cherries. If I want to make a pie, I need a recipe, not a treatise on milling. I think Michael made the recipe pretty understandable, and it allows me to function better as a photographer. Throwing a lot of engineering stuff at me does not, because not only do I not understand it, I don't really care to. That's what engineers are for. No offense.
JC
-
+1 (also no offence to the engineers :))
-
It always amazes / annoys / amuses me when I publish an article that has been painstaking peer-reviewed by some of the brightest minds in the industry – people who design sensors and write raw software (in this instances) and then "experts" whose credentials are unknown tell me (us) why the information in the article is wrong.
This was the case with my original ETTR article. I think I trust Thomas Knoll's knowledge of digital imaging (the original author of Photoshop and Camera Raw) over some online commentator.
Similarly in this instances. I'm sure that there are areas to quibble over (both scientists and artists love to quibble). But when it comes to arcania and subtleties in complex topics I'll continue to trust known experts whose bona fides are well established.
Michael, your article might be absolutely correct but that does not mean that are not additional aspects that can be legitimately discussed. And whenever one tries to simplify things to some extent (which you tried in your article), there can be a legitimate discussion as which aspects got not discussed in full because the simplification omitted them.
-
I don't see why we won't have raw based histograms. As far as I can recall the Leica S2 has raw based histograms but most other cameras have histograms calculated from JPEG. >Don't know why!
We already have UniWB but that still is influenced by JPEG tone curve (even if we try to make that as neutral as possible).
-
Michael, your article might be absolutely correct but that does not mean that are not additional aspects that can be legitimately discussed. And whenever one tries to simplify things to some extent (which you tried in your article), there can be a legitimate discussion as which aspects got not discussed in full because the simplification omitted them.
I have no problem with additional legitimate discussion. My concern is that people without in-depth technical knowledge and expertise simply get confused, and thus turned off when the discussions becomes too arcane.
Michael
-
Just wanted to share some experiences with ETTR and RAW converters. Some of them do not expect images to be taken this way, or at least I have not been able to obtain satisfactory results, at least with programs like Nik Capture NX or DXO Optics Pro (both give very good results with normally exposed pictures and DXO is really good with underexposed pictures). The main issue I get is that even if I can adjust exposure, the image is very dull.
On the other hand, LR/ACR handle ETTR images really well, resulting in vibrant images.
One interesting program I´m testing now is Raw Therapee, which probably is still in an experimental state, but it has a section of RAW preprocessing, that I haven´t seen anywhere else, where you can perform the "normalization" (besides other advanced techniques) before post processing.
-
The amount of recovery in your Niagra Falls shot is astounding, but the raw file is not nearly so clipped as the ACR histogram would suggest, likely because of the BaselineOffset that ACR uses for your camera.
Which is the point I was trying to make...even when an image seems pinned to the highlights with numeric indications of clipping, a lot of that data is simply clumped up in the highlights and can be utilized...guess what the back of the camera on that image looked like? Yep, completely white...but there was a surprising amount of usable detail remaining. Which more than anything proves that exposing to the right isn't nearly as likely to clip highlights if done carefully. And actually, I've been playing with an unannounced raw converter that does even better with the highlights, sorry, can't talk about it :~)
-
Essentially, ETTR is the digital complement to the Exposure component of Ansel Adams' Zone System -- capture as much information as possible in the exposure, with the intention of working with that information in later stages to create an image. It is accomplished differently in digital than in film, i.e., expose to the right instead of expose for the shadows, but the objective is the same.
Understandably, automatic metered film cameras never incorporated this concept, because the expectation was that most users would simply opt for straight processing and printing. Likewise, for digital cameras, the designers' assumption for automatic modes is that the camera should capture an image that is as close as possible to a printable image, which gives up the benefits of having an initial image recorded that includes as much information as possible for later redistribution. Camera makers are unlikely to design their cameras to overexpose without clipping by default, because such images will look terrible if they are simply printed or pulled into iPhoto or Picasa. Unless there is a exposure-boost tag that automatically causes the standard photo programs to crank down the exposure by the same amount, pictures will look without manipulation.
Perhaps a more useful approach would be to use ETTR metering techniques when recording RAW images, on the assumption that anyone using RAW will be processing images individually and will be positioned to take advantage of the improved data capture.
-
Hi!
I don't see why we won't have raw based histograms. As far as I can recall the Leica S2 has raw based histograms but most other cameras have histograms calculated from JPEG. >Don't know why!
Best regards
Erik
Hi Erik
The rumour about S2 raw histograms is incorrect. It is the same as any other camera. I am at the Leica factory this week with access to the technical people. This is a question I want to raise.
-
And actually, I've been playing with an unannounced raw converter that does even better with the highlights, sorry, can't talk about it :~)
This will be interesting to hear more about when you are able to discuss it.
Highlight recovery is hugely important for all the reasons discussed above. Currently, and I'm a big LR3 user/fan, Aperture seems to do the best job at recovering highlights. You can even work with a histogram which actually shows the 'clipped' data ie the data to the right of the 255 point. I have not measured per se, it but I can definitely get better quality highlight recovery and about 0.5 stops more exposure before total blowout compared to LR3. Extra exposure reduces shadow noise, this much is quite clear.
-
I have no problem with additional legitimate discussion. My concern is that people without in-depth technical knowledge and expertise simply get confused, and thus turned off when the discussions becomes too arcane.
Michael
Hi Michael,
I agree completely, and that's why I put my comment on quantization noise vs. read and shot noise only in a P.P.S. about something I thought more relevant (color errors from RAW converters with ETTR) - I think the "levels" argument while not strictly correct is probably a lot easier for most people to understand and nearly functionally equivalent. If the comment wasn't welcome here, my apologies.
Ken
-
Nick,
Enjoy your time in Germany and also meeting with the Leica people!
Best regards
Erik
Hi Erik
The rumour about S2 raw histograms is incorrect. It is the same as any other camera. I am at the Leica factory this week with access to the technical people. This is a question I want to raise.
-
Could someone please explain what happens in the post-processing once the exposure has been "corrected" for darker scenes?
Since major correction is only needed for dark scenes, ignore the near-white, minor correction scenario.
If I save the file as jpeg, aren't I simply throwing out all that good work? Is it pretty much the same as if I had taken jpeg only in-camera (pls ignore any other raw processing effects and assume I'm using the manufacturers converter which applies identical raw->jpeg as in-camera)?
If I save it as 16bit non-raw, say tiff, will the move from 14bit camera -> (I presume) 32 bit lightroom -> 16 bit file throw out any benefit?
I presume that saving to 32 bits won't have any effect (will it?).
Thanks!
PS. I can understand pretty detailed maths, so go to it if you need to
-
Essentially, ETTR is the digital complement to the Exposure component of Ansel Adams' Zone System -- capture as much information as possible in the exposure, with the intention of working with that information in later stages to create an image. It is accomplished differently in digital than in film, i.e., expose to the right instead of expose for the shadows, but the objective is the same.
ge of the improved data capture.
EXACTLY. When viewed this way it is amazing how much is same or parallel to what Ansel wrote in his book The Negative! There is also the book by Chris Johnson "The Practical Zone System" which contain perhaps the best chapter yet written on how the zone system applies to digital capture.
Michael's article discusses solely automatic metering based on ETTR, but is there not also a manual approach of using the Zone system at arriving at an optimized exposure (one shot) at RAW (ETTR)? I would argue that there is on basis of a single spot meter for the brightest highlight in a scene, on basis of knowing how many stops above neutral that occurs for the sensor being used and manually setting exposure for a camera or digital back accordingly. Add to that the ability to visualize Zones I, II, VIII and IX and perhaps Zone V middle tone, and there it is, precisely what Ansel Adams did but applied to digital, except he did so for all zones in order to visualize the image at capture. With digital we can slide the other zones around :).
Thus the only difference to Ansel seems that above is applied to a different media; digital. Ansel applied to B&W film and more in his days but not digital. Thus… not all exposure metering have changed per say but perhaps some have been forgotten? Above is perhaps a manual means of an addition to Michael’s article? ;D
Thereby the basic fundamentals of metering remains the same as they always have... ; with adoption to the media of capture, just like Ansel Adams. For automatic exposure, Michael seem precise right.
Regards
Anders
-
Camera profiles in ACR/LR with lightness-dependent color should not have issues with ETTR, as long as you perform the "normalization" using the Exposure slider, rather than the Brightness slider. For example, if I expose an extra 1.5 stops in the field (relative to how bright I want the actual image to be), then in ACR I would compensate with Exposure -1.5.
Eric
The default setting in ACR isn't linear. There is a contrast boost. If what you state is desirable then the settings should be zeroed out? Adobe should zero the settings as a starting point rather than a contrast boost. At lot of users don't know about this.
-
I thought I understood the ETTR method of exposure and exposure in general but the article has me thinking again.
Quote
In the case of the white cat and snow – yes – you would do the same as for film – increase the exposure so that it looked correct. But in the case of the black cat on the coal pile you would do the opposite of what you would do for film. Instead of decreasing the exposure to make the cat and coal look black, you would increase the exposure the same as you would for the white cat and the snow.
Unquote
Does this mean that every image I take I should have my EV set at plus 1.0 ( or similar ) regardless of the brightness - or lack of it - in a scene and if it is looking pushed to the right in ACR - without it being overexposed - and then simply reducing the exposure till the histogram has an even distribution of data? Up until now I have been using the Digital Zone method with success but I am now wondering about the method being discussed. BTW this whole thread and article is very worthwhile and if someone manages to counter what Michael has stated then it is still informative. :)
-
Does this discussion apply to the electronic viewfinder cameras? I had assumed that the exposure was assessed from the actual sensor data and might be a more accurate reflection of the sensor's capabilities.
-
I've been playing with an unannounced raw converter that does even better with the highlights, sorry, can't talk about it :~)
Raw Therapee does an amazing job at highlight recovery. It has four different choices: Luminance recovery, CIELab Blending, Color Propagation and Blend. It will also show the RAW histogram. Would like to hear about the RAW converter you are testing.
-
I liked Michael's write up and I also like the technical discussion on this thread as well. I read Jeff Schewe's example last year some time when he posted it on another thread and it's quite illuminating. There was also a discussion about Dynamic Range (DR) at that time and what the effective range of various DSLRs is. We all have different equipment based on the type of work we do and our own personal budgets. That being said there is a lot we can test ourselves to find out the limits of what we can and cannot do. After the DR discussion I prepared the attached test shot (really cheap as you can see; mounted my Passport and a test shot to a piece of matboard and duck taped it to a brick wall outside my house; you can see the bricks on the left edge which provides a good color check for the shot). I made a whole series of images based on the original meter reading and then going through various over and under exposures. This gives a good range from which you can then see how LR/ACR works in terms of being able to recover detail and colors with associated noise. I found this quite informative and it gave me a good feeling for how to implement ETTR in the field. It took all of 30 minutes or so to prepare the chart and capture all the images (I also shot it early in the day when the sun was on the other side of the house so that there was even illumination on the chart).
-
Does this mean that every image I take I should have my EV set at plus 1.0 ( or similar ) regardless of the brightness - or lack of it - in a scene and if it is looking pushed to the right in ACR - without it being overexposed - and then simply reducing the exposure till the histogram has an even distribution of data?
Sort of.
You may want to increase exposure up to about 3 stops, or not at all. It all depends on the scene. The important point is to place as much of the data to the right of the histogram, but without clipping any important highlights. The problem (until manufacturers automate this) is that the histogram on your LCD is not based on the real raw data in its very large colour space. This means it's going to yell "clipping" when you still have extra headroom available.
For this reason it's worth doing some testing to see what your particular camera's characteristics are. Keep adding a third of a stop well into clipping (on the LCD histogram) and then look at the files in your raw converter and see when they really do clip. This will tell you how much extra headroom you have.
You can also set your camera to autobracket.
Michael
-
Sort of.
You may want to increase exposure up to about 3 stops, or not at all. It all depends on the scene. The important point is to place as much of the data to the right of the histogram, but without clipping any important highlights. The problem (until manufacturers automate this) is that the histogram on your LCD is not based on the real raw data in its very large colour space. This means it's going to yell "clipping" when you still have extra headroom available.
For this reason it's worth doing some testing to see what your particular camera's characteristics are. Keep adding a third of a stop well into clipping (on the LCD histogram) and then look at the files in your raw converter and see when they really do clip. This will tell you how much extra headroom you have.
You can also set your camera to autobracket.
Michael
Thanks for the feedback. My primary camera is a Nikon d700 and according to DxO I can raise my EV by as much as 3 stops without clipping. I generally use 2 stops to be on the safe side. I have been trying to sometimes expose for dark areas of an image and lowering the EV by 2 stops to prevent blowout of highlights. It was giving me an underexposed image. Now I think I know why after reading your article. Much food for thought. I have used the Uni WB in the past so I am aware of the limitations of the Jpeg histogram. The raising of EV for dark areas is something to try. :)
-
Hi,
Agree with the conclusion, we should to expose to the right and the cameras should support this.
On the other hand I´d say that Michaels explanation of why we should expose to the right is lacking. The reason to expose to the right is mainly that we want maximize signal (which is the number of photons detected). There is no simpler explanation, and it also happens to be the correct one.
Best regards
Erik
When audio recording people went from analog to digital, they went through the same troubles. While analog gear tends to have a somewhat "soft" clipping characteristic (increasing gain will increase distortion but decrease noise), digital tends to have a brick-wall. The solution is to record as "hot" as one dears (a little clipping can be disasterous), and to use components that offers a large capture DR if needed.
I am not sure that I understand why ETTR is discussed so much. I try to get good exposures in camera, but will change according to taste in my editor. For controllable, slowly changing scenes, I think this is a non-issue (at least for me and my quality expectations). For action-scenes where the light is out of my control, I have more issues with finding good aperture and exposure time settings in isolation (getting suitable DOF and motion blur), than with gross exposure errors. Of course, when margins are really low (little light, much movement, large desired DOF, flash unavailable), missing by 1 stop can detract from the usability of the image.
-h
-
Hello,
I don't understand the complete discussion, because what Michael states is not new, but absolutely right !
It is common knowledge that the way a sensor reacts to light is complete different than a chemical film does. So it makes no sense to keep on measuring and interpreting light in the way it was invented for chemical film.
Furthermore, it is also common knowledge that a sensor captures color-depths of 12 to 16 bit. So it makes no sense to show exposure in a heavy reduced range of 8-bit by first creating a jpg.
Perhpas I'm a little simple-hearted, I don't own any Phd in physics, chemestry, or electrical engineering, so for me all said by Michael makes sense and equates my personal experiences.
Best wishes
Robert
-
It always amazes / annoys / amuses me when I publish an article that has been painstaking peer-reviewed by some of the brightest minds in the industry – people who design sensors and write raw software (in this instances) and then "experts" whose credentials are unknown tell me (us) why the information in the article is wrong.
This was the case with my original ETTR article. I think I trust Thomas Knoll's knowledge of digital imaging (the original author of Photoshop and Camera Raw) over some online commentator.
Similarly in this instances. I'm sure that there are areas to quibble over (both scientists and artists love to quibble). But when it comes to arcania and subtleties in complex topics I'll continue to trust known experts whose bona fides are well established.
Michael
If there's one thing that I always enjoy about articles you post it's that you're always involved in discussion about it afterwards. It would be nice if more of your contributors were involved in discussions about their articles - particularly in this forum. Sometimes there's not much to say or be said, but others, yes.
Thanks for being involved.
Darren
-
Michael's article discusses solely automatic metering based on ETTR, but is there not also a manual approach of using the Zone system at arriving at an optimized exposure (one shot) at RAW (ETTR)?
Yes, but if Live View can reliably automate this, why not profit?
There are indeed situations where you have to shoot rather quickly, because of some photographic opportunity passing by (a beam of light on the right spot, the head of the giraffe balancing nicely with the iceberg forms, or you name it), and in those cases I'd really like my camera not to pretend it is loaded with negative film - which seems the hypothesis of my canon DRebel matrix metering, leading generally to burnt-beyond-any-recovery skies eg.
And yes indeed, raw histograms (http://www.luminous-landscape.com/forum/index.php?topic=33267.0) and flashing highlights based on those raw values are needed as XXIth century tools as well.
Adjusting a proper exposure looking at the jpeg file or its values may be a bit like correctly exposing the polaroid positive hoping it will suit the negative part as well.
Because as good the raw converter is, when the raw data is clipped there isn't any info anymore and all that can be done is guesswork (but yes, some converters may guess better than others).
Does this discussion apply to the electronic viewfinder cameras?
Yes, because the sensor works the same way, no matter the viewfinder.
What may be a catch is that you'll see the tonality of the jpeg file in the viewfinder, making it counterintuitive to apply the right setting : a too contrasty scene will appear too dark and a low contrast scene may appear too bright (but as a side note, I would think that low contrast scenes don't benefit as much from ETTR as high contrast ones, because SNR is not a very constraining factor for those).
-
Furthermore, it is also common knowledge that a sensor captures color-depths of 12 to 16 bit.
Although the bits "are there", I think it is common knowledge that the least significant ones tend to be noise (random), and the minute steps at the upper part of the range is largely irrelevant (unless you are going to modify the tonal range a lot).
So it makes no sense to show exposure in a heavy reduced range of 8-bit by first creating a jpg.
Having a way to observe the exposure in-camera that was directly based on the raw file would be great. Now, if it was binned in 256 or 1024 bins probably would not matter much to me - I tend to only care about the head, tail and body of the beast, not the minute scales along its back.
-
The problem (until manufacturers automate this) is that the histogram on your LCD is not based on the real raw data in its very large colour space. This means it's going to yell "clipping" when you still have extra headroom available.
Exactly! The main problem is folks think exposing for a JPEG where the rendering is totally out of their control, and based on this incorrect clipping information applies to the raw data. They think if they see clipping on the LCD, it affects the raw data. Yup, you’ll clip that JPEG and that clipping info is useful if you shot only JPEG!
Expose using a meter (based on film with its H&D curve) and the feedback for JPEG on the camera, you’ll very likely be under exposing the linear raw data. Expose properly (idealized) for the raw based on what you intend to render (the intend here does have a bit of Adam’s thinking in the mix), you’ll very likely blow out the JPEG.
A photographer would never treat (expose and develop) ISO 400 transparency film the same as ISO 100 color neg film. Why should they treat exposure and development of JPEG and raw the same way, considering the vast differences in the data and processing? How do we get the manufacturers to give us a LCD feedback based on the actual data we want to capture?
-
Sort of.
You may want to increase exposure up to about 3 stops, or not at all. It all depends on the scene.
That last sentence really is the key.
My concern is that if ETTR became the default then it would make it harder for a lot of people to shoot "sharp" pictures because ETTR needs more light and that either means slower shutter, wider aperature or higher ISO - none of which are recognised as being better for pixel peeping with. Whilst *I* wouldn't mind an "ETTR mode" rather than a exposure compensation mode, I just can't see that selling cameras that random folks in the street use because it'll be harder for them to get good JPG pictures compared to the other manufacturers' cameras that don't.
The important point is to place as much of the data to the right of the histogram, but without clipping any important highlights. The problem (until manufacturers automate this) is that the histogram on your LCD is not based on the real raw data in its very large colour space. This means it's going to yell "clipping" when you still have extra headroom available.
Something that I've found useful in judging whether something is blown or not is to (temporarily) tune down the exposure in LR to -4. It then becomes quite obvious if there are colour channels that are "blown". Unfortunately I don't know of any way to do that "in camera" :-(
In retrospect, something that might be missing from that article was advice on how to better setup the camera to give more "accurate(?)" histograms - or would that be too camera specific? I think the advice I've used for Canon cameras is to turn the contrast right down. This seems to have given me a more accurate relationship with LR.
-
That last sentence really is the key.
My concern is that if ETTR became the default then it would make it harder for a lot of people to shoot "sharp" pictures because ETTR needs more light and that either means slower shutter, wider aperature or higher ISO - none of which are recognised as being better for pixel peeping with.
Well yes but that’s a lot like saying if you shoot film, and you only have ISO 100 film in the camera, your concern is that if ISO100 became the default then it would make it harder for a lot of people to shoot "sharp" pictures because that film stock needs more light and that either means slower shutter, wider aperature or higher ISO...
That you set your camera at F8@250th shot a JPEG and find that you’ve under exposed the raw just means that exposure is incorrect for raw, you need to run a test to find the actual ISO and exposure settings that produce the correct raw exposure.
In the old days, it was always interesting to run film ISO and exposure tests on color negs. It was a wake up call to find that exposing ISO 400 neg film at ISO 100 produced a vastly superior print (when of course you compensated for the exposure in the enlarger for that process).
-
Well yes but that’s a lot like saying if you shoot film, and you only have ISO 100 film in the camera, your concern is that if ISO100 became the default then it would make it harder for a lot of people to shoot "sharp" pictures because that film stock needs more light and that either means slower shutter, wider aperature or higher ISO...
And you're quite right about that. There were many times that I was on holiday and found myself with ISO 100 film in the camera and faced with 1/10th to get the shot (this was before lenses had IS) so I had to invent ways to "mount" the camera to keep it still or (more often than not), blurry picture. Sometimes I had ISO 200 loaded but rarely more than that. On one occasion I had two cameras - one that I kept loaded with ISO 800/1600 and the other with either 100 or 200. It was a trifle cumbersome. And that was just to get a 19th century film shot that wasn't blurry.
-
One thing that should have been mentioned is that the histogram is generated from the JPEG data, and therefore the camera settings for JPEG need to be as flat as possible to have the histogram come as close to RAW as possible. Why don't manufacturers just base the histogram on RAW data as this would also preclude the false impression of clipping Michael mentions in his article?
Ron Johnson
-
Has anyone used this or something like it. It says you can shoot a series of exposures to determine the DR of your camera. If you knew that, couldn't you exposure compensate more accurately? Wouldn't it even calculate the exposure settings for you?
http://www.sekonic.com/Products/L-758DR/Overview.aspx
-
Something that nobody has mentioned -
Even more ridiculous is that an MF digital back like my Hassy one can only shoot in RAW, but I believe the histogram you see on the LCD is derived not from the RAW but from the JPEG preview. How dumb is that?
John
-
The default setting in ACR isn't linear. There is a contrast boost. If what you state is desirable then the settings should be zeroed out? Adobe should zero the settings as a starting point rather than a contrast boost. At lot of users don't know about this.
stamper, yes, there are contrast curves applied by default (*), but those curves are applied after the lightness-dependent portion of the color profile. The Exposure control, on the other hand, is applied before the lightness-dependent portion of the color profile. This means that if you've used ETTR in the camera or bracketed exposures in the camera, and want to normalize the results afterwards, you should use the Exposure slider because that will get the image values in the appropriate tonal range before the 3D color table is applied.
Eric
(*) Zeroing out the curves as a starting point doesn't make sense for the vast majority of users. Having zero curves would mean a linear scene-referred rendering, which looks ugly. The majority of captured scenes need to be tone-mapped and color-mapped to look acceptable in reproduction (e.g., on a display), and that's what the curves accomplish.
-
In cases of extreme white balance correction, something similar to ETTR (color channel specific) can be achieved by using color compensating filters instead of white balance correction.
Typical examples are shots under incandescent lights, where the blue channel is usually 2-3 stops underexposed compared to the red channel.
-
Isn't the simplest solution to this conundrum two sets of firmware, one for the users who need to have the current jpg emulation since they lack the sophistication to delve deep into how ETTR works and maximizing the image and a second for the professional user who wants these options in the camera menu? The only problem with camera companies doing this is that the professional base is always going to be significantly smaller than the casual user. I cannot believe the amount of programming to achieve this would be that significant (but then I'm not a software engineer). At least this approach would let both parties have their cake to eat.
-
No need for separate firmware for pros. Just have it as a custom function, or selectable from a menu.
Michael
-
stamper, yes, there are contrast curves applied by default (*), but those curves are applied after the lightness-dependent portion of the color profile. The Exposure control, on the other hand, is applied before the lightness-dependent portion of the color profile. This means that if you've used ETTR in the camera or bracketed exposures in the camera, and want to normalize the results afterwards, you should use the Exposure slider because that will get the image values in the appropriate tonal range before the 3D color table is applied.
Riddle me this: why do ACR/LR appear to ignore the "exposure compensation" setting (-1,+2/3,etc) in the raw file? (Well, I might add that at least Canon cameras store this in the CR2 file, I don't know about other vendors.)
Why do I ask this? Because an application of "Auto Tone" in LR almost never moves the exposure compensation like you are suggesting above. Although maybe I'm thinking that "Auto Tone" should be "Auto Expose" of the digital negative?
-
Sort of.
You may want to increase exposure up to about 3 stops, or not at all. It all depends on the scene. The important point is to place as much of the data to the right of the histogram, but without clipping any important highlights. The problem (until manufacturers automate this) is that the histogram on your LCD is not based on the real raw data in its very large colour space. This means it's going to yell "clipping" when you still have extra headroom available.
For this reason it's worth doing some testing to see what your particular camera's characteristics are. Keep adding a third of a stop well into clipping (on the LCD histogram) and then look at the files in your raw converter and see when they really do clip. This will tell you how much extra headroom you have.
You can also set your camera to autobracket.
Michael
I remember reading a post somewhere, I think it might have been LL, where there was specific advice on settings for the LCD to help compensate for this difference. Basically, it made the LCD image look really like something you would reject, but helped offer a more accurate histogram.
-
I remember reading a post somewhere, I think it might have been LL, where there was specific advice on settings for the LCD to help compensate for this difference.
You can compensate a tad to get a bit closer but its still a mile off.
-
It seems to me that Michael is giving us the recipe for a metaphorical pie, while the engineers are telling us how to make flour and grow cherries. If I want to make a pie, I need a recipe, not a treatise on milling. I think Michael made the recipe pretty understandable, and it allows me to function better as a photographer. Throwing a lot of engineering stuff at me does not, because not only do I not understand it, I don't really care to. That's what engineers are for. No offense.
John,
A certain amount of technical understanding is needed to make the best use of your camera. The term ETTR is somewhat misleading, since it suggests that a histogram to the right will give optimal results. It is the number of photons collected that determines the shot noise, which is the primary determinant of SNR in digital cameras. Read noise becomes important in determining noise floor from which dynamic range is determined. I think that we nearly all agree that for a given ISO, the histogram should be to the right. At base ISO an accurate histogram to the right will indicate that the sensor is near saturation and one will obtain optimal SNR and DR. However, what about histograms above base ISO?
When shutter speed and f/stop considerations indicate that the histogram is not to the right, one can increase the ISO setting on the camera to increase the amplifier gain and histogram will move to the right, but exposure will not change because of the above mentioned restraints. An ideal digital capture will lose 1 stop of DR for each doubling of ISO, since only half the number of photons are collected for each doubling of ISO. However, many older digital cameras have less than ideal electronics and read noise decreases with increasing ISO. and the slope of the DR vs ISO curve may be less than 1/2 at low ISOs. This is primarily because of increased read noise at low ISO. Increasing the ISO will decrease the read noise and give a lower noise floor, but there reaches a point where increasing the ISO has a minimal effect on read noise. Beyond this point, increasing the ISO will give a better histogram but will do nothing for dynamic range, but will merely limit highlight headroom and increase the chance of blowing highlights.
One can use the dynamic range vs ISO plot on DXO to determine this point of diminishing returns. When the curve becomes linear, increasing ISO will have minimal effect on read noise. As shown on the plot below, this occurs at about a measured ISO of 700 for the Nikon D3 (the ISO indicated by the camera will be higher with this camera). With this camera there is really no point in increasing the ISO above 800, since you will only decrease highlight head room. Expose as much as possible at a camera ISO of 800 and use the raw converter to increase exposure.
With the D7000, the curve is linear from base ISO and there is no real need to increase the ISO to obtain a "better" histogram. One can expose as much as conditions allow and make up the difference in the raw converter. The appearance of the histogram is irrelevant. The scientific explanation for these considerations is given by Emil Martinec (http://theory.uchicago.edu/~ejm/pix/20d/tests/noise/noise-p3.html#ETTR). The article was written before the D7000 was available.
In summary, a bit of engineering theory may make you a better photographer, but you may keep your head in the sand if you so desire.
Regards,
Bill
-
Isn't the simplest solution to this conundrum two sets of firmware, one for the users who need to have the current jpg emulation since they lack the sophistication to delve deep into how ETTR works and maximizing the image and a second for the professional user who wants these options in the camera menu? The only problem with camera companies doing this is that the professional base is always going to be significantly smaller than the casual user. I cannot believe the amount of programming to achieve this would be that significant (but then I'm not a software engineer). At least this approach would let both parties have their cake to eat.
I think that mainstream DSLRs will continue to have "PictBridge" shortcut buttons, but not functions like this.
The solution seems to be something like remote-controlling your camera from your smart-phone, or some (under-dog?) manufacturer choosing to make available cameras based on something like Googles Android and letting people like LL nerds write simple "apps" that takes control of exposure and simple gui functionality. Only then will the functions that needs 2 weeks of implementation but which caters to <5% of the buyers be available. I look forward to that day. Not because I want to play games on my camera, but because I think that flexibility and openness is a good thing.
-h
-
I was lucky enough to get one of the first X100s outside of Japan in early March.
I was very excited when a few weeks later ACR support was added for the camera. Except, as a long time LR user and having shot nothing but RAW with my Canons for the last 7 years - I don't shoot RAW with the Fuji.
The JPG engine with Auto-DR + Auto-ISO switched on is doing something remarkable. I think it is doing exactly what the engineers here are discussing behind the scenes.
I cannot generally even get close to the JPG performance of the Fuji engine when I shoot RAW and process in LR. Or rather lets say, with a fair amount of work on each image I can get equivalent results 50% of the time. 49% I cannot get it as good and maybe 1% I can improve on the JPG by shooting in RAW, usually it's a WB issue. That's why there is a RAW button on the X100, because they had the A-team on the JPG engine and the B-team on the menus.
In auto-DR you never see clipping in the JPG if you are using A-priority or Program mode. Extensive use of the fill light slider is mandatory in the high-DR modes, but there is so little noise in the shadows it's barely believable, this with the NR switched right down in camera.
Hence my suspicion that it's slightly ironic that Michael has used Fuji X100 images in this article because I reckon Fuji has done exactly what he is berating camera manufacturers for not having done all these years. Never a clipped highlight and tons of shadow detail. :-\
[As an aside, there is a significant benefit to shooting in JPG with the X100, which is that the camera never slows down or becomes unresponsive when writing the JPG files to the card, but writing RAW files is slow, even with a fast 45Mb/s card. It's like a different camera really.]
I have a fair number of sample X100 photos on my blog pages. Probably over-processed for the general tastes of this website, and I'm much more an admirer of Bill Brandt than Ansel Adams, but original files available if anyone wants them. Just PM me.
-
Never a clipped highlight
what is that ?
(http://peri.org.uk/wp/wp-content/uploads/2011/07/Day_For_Me_1_of_36.jpg)
-
Craig,
I believe that the increased DR in the Fuji is accomplished by pushing up the ISO. I say this because if you set DR in the auto setting and ISO in the auto setting the minimum ISO is overwritten based on the DR setting.
I'll have to compare the jpgs to the raw files. Honestly I don't look at them at all.
-
John,
A certain amount of technical understanding is needed to make the best use of your camera. The term ETTR is somewhat misleading, since it suggests that a histogram to the right will give optimal results. It is the number of photons collected that determines the shot noise, which is the primary determinant of SNR in digital cameras. Read noise becomes important in determining noise floor from which dynamic range is determined. I think that we nearly all agree that for a given ISO, the histogram should be to the right. At base ISO an accurate histogram to the right will indicate that the sensor is near saturation and one will obtain optimal SNR and DR. However, what about histograms above base ISO?
When shutter speed and f/stop considerations indicate that the histogram is not to the right, one can increase the ISO setting on the camera to increase the amplifier gain and histogram will move to the right, but exposure will not change because of the above mentioned restraints. An ideal digital capture will lose 1 stop of DR for each doubling of ISO, since only half the number of photons are collected for each doubling of ISO. However, many older digital cameras have less than ideal electronics and read noise decreases with increasing ISO. and the slope of the DR vs ISO curve may be less than 1/2 at low ISOs. This is primarily because of increased read noise at low ISO. Increasing the ISO will decrease the read noise and give a lower noise floor, but there reaches a point where increasing the ISO has a minimal effect on read noise. Beyond this point, increasing the ISO will give a better histogram but will do nothing for dynamic range, but will merely limit highlight headroom and increase the chance of blowing highlights.
One can use the dynamic range vs ISO plot on DXO to determine this point of diminishing returns. When the curve becomes linear, increasing ISO will have minimal effect on read noise. As shown on the plot below, this occurs at about a measured ISO of 700 for the Nikon D3 (the ISO indicated by the camera will be higher with this camera). With this camera there is really no point in increasing the ISO above 800, since you will only decrease highlight head room. Expose as much as possible at a camera ISO of 800 and use the raw converter to increase exposure.
With the D7000, the curve is linear from base ISO and there is no real need to increase the ISO to obtain a "better" histogram. One can expose as much as conditions allow and make up the difference in the raw converter. The appearance of the histogram is irrelevant. The scientific explanation for these considerations is given by Emil Martinec (http://theory.uchicago.edu/~ejm/pix/20d/tests/noise/noise-p3.html#ETTR). The article was written before the D7000 was available.
In summary, a bit of engineering theory may make you a better photographer, but you may keep your head in the sand if you so desire.
Regards,
Bill
Exactly, Bill. The idea of ETTR is becoming more and more nuanced, and IMO outdated, as sensor technology improves, and I think it is oversimplified. The color issues that happen when you expose mid tones a couple of steps past midpoint, plus the near-ISO-less cameras that we are starting to see on the market really put a bunch of asterisks next to the idea of ETTR. It is certainly time to start understanding that exposure is independent of ISO, and more recent cameras are better off boosting gain in the raw converter.
-
what is that ?
Most of my processed pics have crushed blacks and blown highlights. a.k.a. black and white. :) All the blame goes to me though, Fuji almost always (glances around nervously) get it perfect.
I'll dig up the original and post it on flickr. But probably not tonight, wasn't planning on firing up the Mac today. It's getting late.
-
The idea of ETTR is becoming more and more nuanced, and IMO outdated, as sensor technology improves, and I think it is oversimplified.
True, even if as far as I'm concerned I still have difficulties understanding what these hue problems in the midtones really are...
But there will still be one basic truth in ETTR, it's the "expose for the highlights" thing. In digital, clipping siome channel can seldom be recovered, and more often means a lost image.
ETTR means expose border to clipping, but without clipping anything important, and I'd think that's something useful to repeat and important even (or mostly maybe) for the beginners.
-
Michael,
Will or do any of the upcoming tutorial videos demonstrate the practice of ETTR with post processing in ACR/LR?
-
Will or do any of the upcoming tutorial videos demonstrate the practice of ETTR with post processing in ACR/LR?
Yep, in Camera to Print and Screen...
-
But there will still be one basic truth in ETTR, it's the "expose for the highlights" thing.
No...you still don't fully grok it. It's expose "properly" based on the scene contrast range and the dynamic range of your sensor. It's also useful to fully understand what your meter is telling you and to know the difference between a scene with low and high contrast.
If the contrast of the scene is beyond the dynamic range of the camera, then you have to choose the relative importance of highlight vs shadow detail and expose to maintain the detail that's important to you...either that, or combine multiple exposures to get the final contrast range you want. Don't forget that ETTR also applies when you do HDR combos because you'll generally want to use the lighter exposures in the deep shadows and darker exposure for the highlights.
-
Schewe's point is important. Often people will take ETTR too literally and protect even specular highlights from clipping and under-expose enough to plunge the shadows into the noise floor - sacrificing the meat of the scene for highlights that don't really have any detail in them anyhow....
Graeme
-
Even more ridiculous is that an MF digital back like my Hassy one can only shoot in RAW, but I believe the histogram you see on the LCD is derived not from the RAW but from the JPEG preview. How dumb is that?
Nope, likely Hassy works same way as does Leica S2, Leaf and Phase One and derives the histogram from the raw data. See here http://www.luminous-landscape.com/forum/index.php?topic=49859.0
-
To further my post #36 above there are in essence two means to meter precisely for ETTR without trial and error. Michael’s is for automation. The other is using a spot meter when knowing (having predetermined) the sensor’s precise limits of DR and simply knowing how many stops above and below mid tone it is capable to capture. The mid tone is because that is what we set aperture and shutter to on lens/camera. Thus when spot metering one would not necessarily need to refer to a histogram since one can already visualize the scenes by measuring tonal values using the spot meter (same as Ansel Adams did). The two methods are for different purposes, same as different types of metering (scene vs. spot) have been used for film capture for years. The “new” is that they need to be applied to the media used, thus to digital as compared to B&W, slides, Polaroid etc, all of which have different DR.
Has anyone used this or something like it. It says you can shoot a series of exposures to determine the DR of your camera. If you knew that, couldn't you exposure compensate more accurately? Wouldn't it even calculate the exposure settings for you?
http://www.sekonic.com/Products/L-758DR/Overview.aspx
Have not used it, but per http://www.sekonic.com/Portals/0/Products/Sekonic_Brochure.pdf
"The Sekonic L-758dr incorporates a precise 1-degree, reflected light spot meter."
"The key to working with the L-758dr’s spot meter is knowing the dynamic range of your camera. That is, the tonal range your camera is capable of recording. Program this into the L-758dr and you can easily know which details will be properly imaged and which will be over or under the range of your camera."
It reads as it functions to give a programmed guide using the limit points of the DR capability of the sensor. What Sekonic enables to determine are the upper and lower clip points from Ansel Adam’s zone system using their ($$) calibration target:
Zone 0 = Pure black (no detail)
Zone X = Pure white: light sources and specular reflections (blown out)
As is e.g. described in Ansel’s books also a concrete wall or similar can be used as a neutral target and using the meter to determine +1, +2 etc test exposures. Ansel determined intermediate zones at each stop in order to help him precisely visualize the image at capture. Thereby the zone system enabled him to at capture know how he could best expose for achieving the optimum print and for the adjustments he would later make during the printing process (or as with digital we do during processing). I pointed out zones I, II, VIII and IX as valuable to digital in my post above because those are the ones that have information (as compared to 0 or 255 which have no texture or tonal info).
Zone I = Near black, with slight tonality but no texture
Zone II = Textured black; the darkest part of the image in which slight detail is recorded
Zone VIII = Lightest tone with texture: textured snow
Zone IX = Slight tone without texture; glaring snow
In contrast to the Sekonic L-758DR the now old Pentax digital spot meter works fine and is far more simpler. ;)
Regards
Anders
-
Hi,
Nick Rains just posted on this discussion that Leica S2 derives histogram from JPEG, he should have good info, as he is at Leica factory right now and talking to their engineers.
Best regards
Erik
Nope, likely Hassy works same way as does Leica S2, Leaf and Phase One and derives the histogram from the raw data. See here http://www.luminous-landscape.com/forum/index.php?topic=49859.0
-
Hi,
This is a good point. It also shows a limitation of the histogram, namely that you don't know what part of the image parts of the histogram correspond to. Sony/Minolta has also blinking highlights.
Anders "HK" has a good suggestion to use spotmeter and overexpose a predetermined number of stops on highlight detail. I used to that when I shot slide film. Negative film was exposed for shadows while slide film was exposed for highlights.
With digital we want to have maximum information and that really means that we can capture as many photons as possible.
On the other hand, there is no reason to overdo! I don't think that exposure differences below one stop really affect shot noise that much and mothern cameras seem to be pretty good at keeping read noise unvisible.
Best regards
Erik
Schewe's point is important. Often people will take ETTR too literally and protect even specular highlights from clipping and under-expose enough to plunge the shadows into the noise floor - sacrificing the meat of the scene for highlights that don't really have any detail in them anyhow....
Graeme
-
John,
A certain amount of technical understanding is needed to make the best use of your camera. <big snip> In summary, a bit of engineering theory may make you a better photographer, but you may keep your head in the sand if you so desire.
Regards,
Bill
No, it won't make *my* photography any better -- I concede that it may make yours better. When I'm shooting, I don't have time to think about that stuff, because I'm thinking about too many other things. If all the engineers and Michael get together and decide Michael's article wasn't accurate, I'd be extremely interested in knowing that. What I then want from them is a recipe, or a prescription, or rules-of-thumb, for what is roughly, probably, maybe, the best practice under a set of given conditions, in and out of trees and hot sunlight, into heavily shaded doorways, through windows into the street, and from the street through windows to the inside. I don't expect the rules to give me perfect exposures, or even the best possible under the conditions, I just want them to be very good. I use automatic settings and autofocus a lot, because sometimes that's the best I can do with a reasonable chance of success. When possible, I'd like to go to the best fast manual set-up I can get, to see if I can kick up the quality a notch. I use rough ETTR rules some of the time, using ISOs of 160-800 (RAW) on several Panasonic m4/3 cameras with zoom lenses and a Pentax K5 with pancake primes and exposing to the right, as had been recommended here, and trying to get back as much as I can in Lightroom. That has actually seemed to me to work, though my shots fail a lot because of camera shake, poor framing, inaccurate focus and so on. If the engineers here would like to give me a set of rules-of-thumb (which is what I've done with Michael's articles -- I've boiled them down to rules) I would be very interested in seeing them, and grateful to anyone who'd provide them. That's about the most I can work with. I really don't have time for analysis or calculation, or even a lot of rules. Five rules would be about as many as I can handle; any more than that, and they'd slow me down too much.
JC
-
Nope, likely Hassy works same way as does Leica S2, Leaf and Phase One and derives the histogram from the raw data. See here http://www.luminous-landscape.com/forum/index.php?topic=49859.0
As Eric has said, NR reports that Leica derive the histogram from the JPEG preview. As far as my own CFV back goes, I have no firm data, but I notice all the time that the histogram and the firmware warnings report over exposure when the image is just fine in LR.
John
-
Schewe's point is important.
I fully agree, and was trying to oversimplify a bit (or put in a better way, foresee the point where even Canon sensors will have too much DR - may not happen that soon).
To further my post #36 above there are in essence two means to meter precisely for ETTR without trial and error. Michael’s is for automation. The other is using a spot meter when knowing (having predetermined) the sensor’s precise limits of DR and simply knowing how many stops above and below mid tone it is capable to capture.
And you may add a method where some raw based blinking highlights are displayed while on live view, and you decide what to burn (that's close to trial and error but you don't waste a shoot, and it's not really slower than the spot method).
PS just to say the obvious : for zone system reasoning, keep in mind that there is a hard edge between Zone 0 (burnt, no detail at all) and Zone I (where the textures are the most detailed) and a very broad transition from Zone VI to zone X with the noise gradually kicking in, in contrary to a film shoulder and foot which are both gradual.
In the digital case the optimal zone is near the highlight edge (let's call that Zone I), whereas with film the optimal zone is in the middle of the linear part of the curve (which should be more or less around Zone V).
-
No, it won't make *my* photography any better -- I concede that it may make yours better. When I'm shooting, I don't have time to think about that stuff, because I'm thinking about too many other things. If all the engineers and Michael get together and decide Michael's article wasn't accurate, I'd be extremely interested in knowing that. What I then want from them is a recipe, or a prescription, or rules-of-thumb, for what is roughly, probably, maybe, the best practice under a set of given conditions, in and out of trees and hot sunlight, into heavily shaded doorways, through windows into the street, and from the street through windows to the inside. I don't expect the rules to give me perfect exposures, or even the best possible under the conditions, I just want them to be very good. I use automatic settings and autofocus a lot, because sometimes that's the best I can do with a reasonable chance of success. When possible, I'd like to go to the best fast manual set-up I can get, to see if I can kick up the quality a notch. I use rough ETTR rules some of the time, using ISOs of 160-800 (RAW) on several Panasonic m4/3 cameras with zoom lenses and a Pentax K5 with pancake primes and exposing to the right, as had been recommended here, and trying to get back as much as I can in Lightroom. That has actually seemed to me to work, though my shots fail a lot because of camera shake, poor framing, inaccurate focus and so on. If the engineers here would like to give me a set of rules-of-thumb (which is what I've done with Michael's articles -- I've boiled them down to rules) I would be very interested in seeing them, and grateful to anyone who'd provide them. That's about the most I can work with. I really don't have time for analysis or calculation, or even a lot of rules. Five rules would be about as many as I can handle; any more than that, and they'd slow me down too much.
JC
I think if you have read and fully digested what has been written in this thread then there should be enough information for you to work out a method to suit your needs. It looks like you are a man in a hurry, more so than most photographers. I have certainly refined useful information from this thread. The forum at times is full of threads which imo isn't about photography. One recent one was about credit cards and the i phone. This thread is one of the best in a long while with respect to photography and Michael should be thanked for it. :)
-
PS just to say the obvious : for zone system reasoning, keep in mind that there is a hard edge between Zone 0 (burnt, no detail at all) and Zone I (where the textures are the most detailed) and a very broad transition from Zone VI to zone X with the noise gradually kicking in, in contrary to a film shoulder and foot which are both gradual.
In the digital case the optimal zone is near the highlight edge (let's call that Zone I), whereas with film the optimal zone is in the middle of the linear part of the curve (which should be more or less around Zone V).
Unquote
There isn't a perfect solution to everything. This shouldn't stop anyone from using the method. Using the digital zone where it is most useful and using what Michael has written in other circumstances is possibly a good work flow which I personally will pursue. 8)
-
"No, it won't make *my* photography any better -- I concede that it may make yours better. When I'm shooting, I don't have time to think about that stuff, because I'm thinking about too many other things. If all the engineers and Michael get together and decide Michael's article wasn't accurate, I'd be extremely interested in knowing that. What I then want from them is a recipe, or a prescription, or rules-of-thumb, for what is roughly, probably, maybe, the best practice under a set of given conditions, in and out of trees and hot sunlight, into heavily shaded doorways, through windows into the street, and from the street through windows to the inside. I don't expect the rules to give me perfect exposures, or even the best possible under the conditions, I just want them to be very good. I use automatic settings and autofocus a lot, because sometimes that's the best I can do with a reasonable chance of success. That's about the most I can work with. I really don't have time for analysis or calculation, or even a lot of rules. Five rules would be about as many as I can handle; any more than that, and they'd slow me down too much. JC "
My edited cut from John’s post, above, really sums up the practicalities of photography as a thing you do, and not as some esoteric process that, unless you work in a studio on still life or/and with standardised lighting, generally happens more quickly than you think – in Ferris Beulers’s words: you could miss it.
My simple solution – with Nikon – is Matrix. Trust it.
In the case of something like a very narrow slice of the frame, say an outside scene shot from well within a darkish room, you can even apply the emergency film 'sunny sixteen' maxim of using the ISO speed as shutter setting and setting the aperture at around 11/16, but, of course, you use whatever combination of that value suits the image. If I can find it, here’s an example. It was easy with film transparencies – you used the incident light meter or, short of access to the same lighting source as on the subject, you could spot meter a white face and open up a stop-and-a-half. Done.
Rob C
-
Hi,
The zone system was mainly used for negtive to positive process. Exposure was for shadow which is zone 1. The zone system adjusts film development as to obtain a complete tonal scale stretching from Zone 1 to Zone IX. Mapping of tone was done in printing.
With digital we don't have a film a tone curve, the sensor response is essentially linear, that is, the "curve" is almost a straiht line. So what we do is to make the straight line as long as possible (that is exposing to the right) and we bend it to our needs in development.
The photography of Ansel Adams built on intimate knowledge of all components of the process:
Choosing emulsion for subject
Choosing exposure for planned development
Choosing developer and development method
Choosing paper and developer for printing
Pretty much engineering...
Best regards
Erik
PS just to say the obvious : for zone system reasoning, keep in mind that there is a hard edge between Zone 0 (burnt, no detail at all) and Zone I (where the textures are the most detailed) and a very broad transition from Zone VI to zone X with the noise gradually kicking in, in contrary to a film shoulder and foot which are both gradual.
In the digital case the optimal zone is near the highlight edge (let's call that Zone I), whereas with film the optimal zone is in the middle of the linear part of the curve (which should be more or less around Zone V).
Unquote
There isn't a perfect solution to everything. This shouldn't stop anyone from using the method. Using the digital zone where it is most useful and using what Michael has written in other circumstances is possibly a good work flow which I personally will pursue. 8)
-
Yes, the zone system was simplified (read often applied) to B&W and in tad different way to slide film and polaroid. Albeit the interesting is that the fundamental zone system in its basics applies same to any media, also digital and ETTR.
Engineering? Same as Ansel but extension thereto is what we do from capture of image thru processing RAW thru print... Things have changed, yet they really have not :)
-
I'm not sure that the participants on this forum, or even those who just drop by to read the features, represent the greater real world of camera users, which is why I think we're not likely to see an ETTR implementation any time soon. (The one exception I could see may be in top of the line bodies, but even there, there point and shooters probably make up the majority of buyers.) As long as the world of RAW shooters consists mostly of people who believe RAW means you don't have to pay any attention at all to camera settings, least of all exposure, you can just wrench a lovely image out of the file - ETTR bias in a camera will produce nothing but loud howling on the digital camera forums. In workshops I've assisted, I can't remember one person who knew that the histograms were from JPG/sRGB representation of the data captured. There are times when I wanted to tape over the LCD... I know there's a pervasive belief that doing your white balance in RAW saves everything -I like to show people files of jazz musicians shot in clubs with gelled stage lights - depending on the perversity of the person who picked the gels, sometimes there are channels completely devoid of information to work with.
I remember early digital point and shoots and DSLR bodies... on a couple of them, there was not such a huge bias exposure bias towards the dark side, and digital forums erupted in anger about blown highlights. The generalized prescription became "set your meter to -EV.7, always". Funny how that's hung on. The dynamic range of the sensors was a lot smaller then - I always felt like I was shooting transparency film then, where now I feel like I'm shooting negative film. In Ye Olde Filmic Tymes I remember having to shift mental gears on the few occasions when I shot negative film instead of transparencies. My metering (and meter, marked up with pens) was biased towards maximum tolerable highlight loss because I usually shot transparencies, but when I had negative film in the camera, I had to adjust my thinking considerably to make sure I got enough info on the film.
My general solution is that I still carry an incident light meter, and I use it often in situations where I know there's a huge spread from brightest to darkest. There are very, very few situations where the incident reading results in a bad file, and I've learned what those situations look like... and a stop up and down bracket almost always get me home.
-
"No, it won't make *my* photography any better -- I concede that it may make yours better. When I'm shooting, I don't have time to think about that stuff, because I'm thinking about too many other things.
So the exposure of the image doesn’t enter the picture at all?
My simple solution – with Nikon – is Matrix. Trust it.
Well then you can use that simple solution AND expose properly for raw (ETTR) if your camera has something as simple as exposure compensation! It will not make your pictures better, agreed. It will make the data better, if that’s important to you (and I’ll freely admit, its not for everyone).
-
As long as the world of RAW shooters consists mostly of people who believe RAW means you don't have to pay any attention at all to camera settings, least of all exposure, you can just wrench a lovely image out of the file - ETTR bias in a camera will produce nothing but loud howling on the digital camera forums.
I don’t believe that’s generally perceived by educated photographers who understand what raw provides. They know only exposure and ISO (and none of the other JPEG settings) affect the raw data.
In workshops I've assisted, I can't remember one person who knew that the histograms were from JPG/sRGB representation of the data captured.
When shooting raw? That’s sad and I suggest not going to such workshops if that isn’t made abundantly clear to the audience. Note, the Histogram could represent an Adobe RGB (1998) representation of the JPEG data, not that helps the raw shooter.
There are times when I wanted to tape over the LCD...
Lets not throw the baby out with the bath water. Its darn useful. Just tape over the Histogram (I keep mine off).
My general solution is that I still carry an incident light meter, and I use it often in situations where I know there's a huge spread from brightest to darkest. There are very, very few situations where the incident reading results in a bad file, and I've learned what those situations look like... and a stop up and down bracket almost always get me home.
I’d agree an incident meter tells us something different and often less of a lie than a reflective meter assuming one doesn’t fully understand the lie the reflective meter can provide. But using either, its important to understand that the meters are still thinking about film with a classic H&D curve, not linear encoded raw data and as such, even with the most accurate incident meter, setting the camera this way will not implement ETTR by itself. One still has to understand where and how highlights clip based on the raw data and the raw converter.
-
I'm not sure that the participants on this forum, or even those who just drop by to read the features, represent the greater real world of camera users, which is why I think we're not likely to see an ETTR implementation any time soon. (The one exception I could see may be in top of the line bodies, but even there, there point and shooters probably make up the majority of buyers.)
Sorry, but I can't agree. This site gets about 1.3 million unique readers each month. Unlike many photo sites that are much bigger (DPReview and similar) this is a site about photography, not just reviews of the latest cameras. Technical articles, like the one on Optimizing Exposure, get literally hundreds of thousands of readers over the course of a year. This shows the level of interest.
Most casual photographers shoot JPGs and post to sites like Flicker. But there is a huge world-wide audience of people who care about the technology of photography and optimizing image quality. Manufacturers ignore them at their peril.
Michael
-
Most casual photographers shoot JPGs and post to sites like Flicker. But there is a huge world-wide audience of people who care about the technology of photography and optimizing image quality. Manufacturers ignore them at their peril.
Michael
It's all about maximising the quality of your data capture, and also capturing all the data that is in the scene. If you have a scene that is too contrasty for a single capture, shoot more than one frame at different exposures. If the contrast of the scene will fit in the camera's DR then, if you want to squeeze the last drops of tonal quality out of your camera, then you need to put the data into the region of the camera's range which has the highest number of tonal steps available. ie ETTR. Even if the scene is of modest contrast (if I am working off a tripod) I will often shoot a second exposure at plus 2 just to capture better shadow detail. Then, if shadow detail is critical to the quality of my final image, I have a reserve of data I can dip into. Pixels are free, why not take that second shot, just in case you need its data? Its the work of 5 seconds to do and if you don't need it, well nevermind.
In the field, you do the best you can. If you have the time, shoot carefully using LiveView and watch your histograms. If you don't have time, trust your meter and learn how it behaves in different lighting situations.
-
Yep, in Camera to Print and Screen...
In terms of arrival date for this tutorial, what sort of expectations should we have? CY2012? CY2011?
-
1 week
-
The visual aid I'd like to have in the camera is similar to the blinking blown out highlight present today in most cameras, but implemented in a different way:
1.- based on Raw values
2.- Both highlights & shadows (maybe different color for each)
3.- User configurable thresholds
The user configurable threshold would be useful especially for the shadows, since it could be adjusted to the acceptable noise level (I.E. on a 0-255 scale I'd like to be warned about any value below 7).
This will help prevent important parts of the image getting down in the shadows while protecting the highlights.
-
So the exposure of the image doesn’t enter the picture at all?
Well then you can use that simple solution AND expose properly for raw (ETTR) if your camera has something as simple as exposure compensation! It will not make your pictures better, agreed. It will make the data better, if that’s important to you (and I’ll freely admit, its not for everyone).
A bit of a mixed up response: the part of the post credited to me that instigated your first sentence was a quotation from John, not a direct one from myself! As for making my pictures better, that wouldn't demand an exposure function, it would require a mind transplant.
Regardless of who wrote what, I don't quite see how you can extrapolate what was written into a suggestion/interpretation that anyone was saying "exposure doesn't enter the picture at all"! Of course it does; that's why the plug for Matrix metering. It measures exposure and, without further alteration at shooting stage, gives pretty reliable results. I refer here to shooting where you don't have the luxury of either static subjects or plenty of repeat time, which I expect is closer to most realities than the heavy, dusty Gitzo and stepped exposures. At any rate, it sure is closer to mine and, from what I read, John's. No opinion caters perfectly for all - mine is jut what fits my current world.
Rob C
-
Of course it does; that's why the plug for Matrix metering. It measures exposure and, without further alteration at shooting stage, gives pretty reliable results.
Yes but not based on ETTR (not without having a specific idea how much more exposure can be used prior to blowing out highlights you don’t want blown out). Incident meter, reflective meter, matrix, all are only as good as the person setting them for ideal exposure (in this context raw). Simply setting the camera ISO (or meter ISO) and taking a reading doesn’t take ETTR into account. In fact you’ve got to test the sensor and the raw converter before you know how far you can expose to the right. The meters have no idea of this. Much as the ISO written on a box of film was, without any testing of exposure and development, simply a starting point. It gave pretty reliable results but hardly ideal results.
-
Furthermore, it is also common knowledge that a sensor captures color-depths of 12 to 16 bit. So it makes no sense to show exposure in a heavy reduced range of 8-bit by first creating a jpg.
Robert
Robert,
Linear encoding as with current raw formats is very inefficient since it uses most of its bits in recording redundant levels towards the bright end of the image and too few bits for the shadow areas. Gamma encoding such as with JPEGs redistributes bits towards the shadows where the are needed. Norman Koren (http://www.normankoren.com/digital_tonality.html) gives a good explanation on his web site. A gamma 2.2 8 bit image can represent the visible levels in a 12 bit linear file but barely. For true HDR, a linear 16 bit encoding is entirely inadequate. Gamma encoding extends the DR, but for real HDR one must go to log or floating point encoding. See Greg Ward (http://www.anyhere.com/gward/hdrenc/hdr_encodings.html).
Regards,
Bill
-
In theory, in linear encoding there is a direct relationship between the minimum number of bits needed for a given DR, so for 12 f/stops DR you need at least 12 bits (the inverse is not true, you will not increase the DR by increasing the number of bits, because noise will be a limiting factor)
With gamma encoding, this relation changes to minimum number of bits = gamma x DR, so with 8 bits and gamma 2.2 you could represent 8 x 2.2 = 17.6 f/stops DR from an original scene, more than your 12 or 14 original linear RAW.
Gamma encoding is not used only in JPegs, it is used also in Tiffs
This of course is theoretical, since if you don't have information to begin with, you will not have it at the end, but it is important to know that you cannot compare directly them (12-14 bits linear RAW vs 8 bit Jpeg / Tiff).
I'm a believer of editing in linear 16 bits, keep RAW as long as possible, but once you're done with your editing, a 2.2 Gamma encoded 8 bit TIFF is more than adequate for most uses (except maybe high end printing)
-
With gamma encoding, this relation changes to minimum number of bits = gamma x DR, so with 8 bits and gamma 2.2 you could represent 8 x 2.2 = 17.6 f/stops DR from an original scene, more than your 12 or 14 original linear RAW.
I'm a believer of editing in linear 16 bits, keep RAW as long as possible, but once you're done with your editing, a 2.2 Gamma encoded 8 bit TIFF is more than adequate for most uses (except maybe high end printing)
I don't know where you get your 8 bit gamma 2.2 DR of 17.6 f/stops. In his post on encoding (http://www.anyhere.com/gward/hdrenc/hdr_encodings.html), Greg Ward gives the DR of 8 bit sRGB at 1.6 orders of magnitude. 10^1.6 = 39.81 or 5.32 f/stops.
Microsoft has proposed a scRGB standard for HDR. The first uses 12 bits per channel and a gamma of 2.2 with a linear ramp for the deep shadows and has a DR of 3.2 orders of magnitude or 10.6 stops. The other uses 16 bits per channel and a linear ramp, giving a DR of 3.5 orders of magnitude or 11.6 f/stops. See Table 1. This is for a cutoff error of 5% at the lower end of the ramp and differs from the oft quoted 1 f/stop per bit, where the error would be larger. He says that the eye can often notice differences of 2% in the shadows.
With these considerations in mind, I would not recommend 8 bit sRGB for current digital cameras with good DR, although it is suitable for most current printers. However, high DR monitors are becoming available and more than 8 bits are needed for them.
Regards,
Bill
-
For anything gamma-related, I think the works of Poynton is of great value:
http://www.poynton.com/PDFs/GammaFAQ.pdf
12 What is contrast ratio? Contrast ratio is the ratio of intensity between the brightest white and the
darkest black of a particular device or a particular environment. Projected
cinema film, or a photographic reflection print, has a contrast ratio of
about 80:1. Television assumes a contrast ratio, in your living room, of
about 30:1. Typical office viewing conditions restrict the contrast ratio of a
CRT display to about 5:1.
13 How many bits do I need
to smoothly shade from
black to white?
At a particular level of adaptation, human vision responds to about a
hundred-to-one contrast ratio of intensity from white to black. Call these
intensities 100 and 1. Within this range, vision can detect that two intensities are different if the ratio between them exceeds about 1.01, corresponding to a contrast sensitivity of one percent.
To shade smoothly over this range, so as to produce no perceptible steps,
at the black end of the scale it is necessary to have coding that represents
different intensity levels 1.00, 1.01, 1.02, and so on. If linear light coding is
used, the “delta” of 0.01 must be maintained all the way up the scale to
white. This requires about 9,900 codes, or about fourteen bits per component.
If you use nonlinear coding, then the 1.01 “delta” required at the black
end of the scale applies as a ratio, not an absolute increment, and
progresses like compound interest up to white. This results in about 460
codes, or about nine bits per component. Eight bits, nonlinearly coded
according to Rec. 709, is sufficient for broadcast-quality digital television
at a contrast ratio of about 50:1.
If poor viewing conditions or poor display quality restrict the contrast
ratio of the display, then fewer bits can be employed.
If a linear light system is quantized to a small number of bits, with black
at code zero, then the ability of human vision to discern a 1.01 ratio
between adjacent intensity levels takes effect below code 100. If a linear
light system has only eight bits, then the top end of the scale is only 255,
and contouring in dark areas will be perceptible even in very poor
viewing conditions.
However, high DR monitors are becoming available and more than 8 bits are needed for them.
Regards,
Bill
Even for new monitors that could gain from >8 bits, it is difficult to actually do. Photoshop does not support >8bits for rendering afaik. Most graphics APIs, drivers etc is hardwired for 8bpc. DVI/HDMI should be able to support >8bits, but for some reason it is not used. Rather, my shiny new Dell monitor supports 10 bits over DisplayPort, but then goes on to warn me against using it because of issues with wake from resume...
-h
-
In terms of arrival date for this tutorial, what sort of expectations should we have? CY2012? CY2011?
The first files of Camera to Print & Screen (http://www.luminous-landscape.com/forum/index.php?topic=55786.0) will be released on or about August 8th.
Forum readers may wish to check the Store sometime on Sunday August 7th as that is when I will be making the product 'live' prior to its announcement on What's New on August 8th
-
Yes but not based on ETTR (not without having a specific idea how much more exposure can be used prior to blowing out highlights you don’t want blown out). Incident meter, reflective meter, matrix, all are only as good as the person setting them for ideal exposure (in this context raw).
The recent Nikon Matrix metering is fairly sophisticated. It uses 1005 sensors and can detect the contrast of a scene as an aid in determining exposure according to its internally stored database. However, with my D3, the matrix often underexposes with high contrast scenes and you have to watch the histogram and correlate how the histogram displayed by the camera correlates with the raw data. It is still 12-18% overall scene based and a shot in dense fog will give a low contrast image with the histogram peaking in the center and a large empty space in the right portion of the histogram.
It would seem that these 1005 sensors could be used for automated ETTR exposure. Not as good as a live view method, but perhaps usable. It could ignore the brightest 5% (I am only guessing here) or so of the brightest areas as specular highlights and then set exposure such that the next brightest pixels are near saturation.
Regards,
Bill
-
It would seem that these 1005 sensors could be used for automated ETTR exposure.
That’s the key. 1005 or 105 sensors, its being programed to deal with raw, ETTR that’s the issue. But you can do that with a single spot meter read too. Its about ‘calibrating’ the exposure system and targeting the exposure that’s key and that’s mainly and educational process. We have to stop thinking as if we are exposing film (and would that film be neg or chrome?).
-
It would seem that these 1005 sensors could be used for automated ETTR exposure. Not as good as a live view method, but perhaps usable. It could ignore the brightest 5% (I am only guessing here) or so of the brightest areas as specular highlights and then set exposure such that the next brightest pixels are near saturation.
But if the science of exposure is being able to have the brightest pixel just at the clipping point, then the art of exposure would be figuring out the scene-dependent proper threshold for clipping some percentage of the pixels, would it not? If there is a light-bulb in your picture, you might want to clip those pixels and instead get good exposure of the remaining 95%. But of you are shooting fireworks at night-time, the situation may be opposite. I dont see how any automated algorithm could guess my intentions from those two?
-h
-
That's why, as proposed in the article, there needs to be a user configurable threshold adjustment.
Michael
-
That’s the key. 1005 or 105 sensors, its being programed to deal with raw, ETTR that’s the issue. But you can do that with a single spot meter read too. Its about ‘calibrating’ the exposure system and targeting the exposure that’s key and that’s mainly and educational process. We have to stop thinking as if we are exposing film (and would that film be neg or chrome?).
True, but with a 1 degree spot meter you have to find the brightest area of the subject where you want highlight detail and then increase exposure by about 2.5 stops as Bruce Fraser suggested years ago. An automated system can't make that judgement for you but with 1005 readings and some threshold for neglecting specular highlights that can be blown, it should be able to come close.
I don't see the relationship to film, except that most spot meters are calibrated for mid-gray but merely read luminance and one can convert to lux (lumens per square meter) if desired and do whatever one wants with the reading. However the ISO saturation standard for digital sensors (ISO 12232) also involves mid gray (18%) with a half stop for headroom. A digital camera calibrated to the ISO standard for light meters should give 12% saturation when one exposes according to the meter reading, the same as with film.
Regards,
Bill
-
I don't know where you get your 8 bit gamma 2.2 DR of 17.6 f/stops. In his post on encoding, Greg Ward gives the DR of 8 bit sRGB at 1.6 orders of magnitude. 10^1.6 = 39.81 or 5.32 f/stops.
I had an error in my previous post writing the equation, but the result is correct.
With gamma encoding, you are able to represent a higher dynamic range from the original scene with less bits, otherwise it would be a waste of time to do it so:
Minimum number of bits = DR / Gamma
If you look in the table in the Norman Koren (http://www.normankoren.com/digital_tonality.html) page you referenced, you´ll see that for exposure zone 11, you don´t have any levels if you use 10 bit linear RAW but you still have 3 levels with 8bits at 2.2 gamma encoding
I haven´t studied yet the article by Greg Ward, but maybe that´s something related to sRGB and not to gamma encoding
-
True, but with a 1 degree spot meter you have to find the brightest area of the subject where you want highlight detail and then increase exposure by about 2.5 stops as Bruce Fraser suggested years ago. An automated system can't make that judgement for you but with 1005 readings and some threshold for neglecting specular highlights that can be blown, it should be able to come close.
Actually the beauty is that with a 1 degree spot meter we are back to the same simplicity as Ansel Adams! ;) It means that we as a photographer are in control for judging exact and precise where we wish to place the threshold for bright point (whether we prefer zone 0, I or II) and that we do not leave such decision to the automation meter in our camera. This is the ultimate full control.
Same as Ansel we also need to know what is critical for our exposure for the specific media we use, thus in our case how much above neutral is the bright point, and which is not dependent on Bruce Fraser's recommendation of 2.5 stops but on the performance of the specific sensor in our camera. Thus we need test sensor for this in order to be assertive. Thus indeed we SHOULD think of it like FILM, albeit the film in our camera being a sensor of an emulsion with DIFFERENT PERFORMANCE and CHARACTER than B&W film, slides or polaroids, all of which had different performances and characters. With digital we look primarily at bright point and a specific and large DR for our specific sensor.
Why neutral? This is what our aperture, shutter and the whole of stops and metering in photography is based upon. ;)
Contrary to Ansel though, we do not necessarily need to scan a scene with the spot meter to find more points if we are lazy, which we could... if we wanted to determine also the other end of DR and want to evaluate the scene for intermediate, e.g. mid tone. Using a spot meter though, it happens we could essentially also put tape over our histogram..., low and behold :D
-
Hi,
My suggestion would be that camera exposes ETTR when shooting RAW and in camera JPEG is compensated for the overexposure, histogram and blinking highlights should be based on the raw image.
The camera should make some educated guess on what highlights are spectacular. Most cameras already have exposure compensation, so that option could also be used to bias/shift automatic ETTR exposures.
On the other hand, I don't feel we need to overdo this. There are two reason to ETTR, one is to keep down shoot noise, and on many cameras the best option is to use base ISO. For low contrast subjects I'd suggest that exposing for mid gray would give good enough image quality, even if we could improve the image quality somewhat by exposing fully to the right.
When we have a high contrast scene we need to fully optimize dynamic range and want to be able to produce clean shadows which can be show read noise (which is more disturbing than "shot noise"), the best way to keep shadows clean is to collect as many photons as possible so "signal" in the shadows area will be as good as possible.
In low contrast situations I'd say that increasing exposure by one stop will have very small effect on image quality. Increasing exposure two stops would double signal to noise ratio and may be noticable.
In high contrast situations doubling exposure doubles dynamic range, so even half a stop may matter.
Best regards
Erik
That's why, as proposed in the article, there needs to be a user configurable threshold adjustment.
Michael
-
The camera should make some educated guess on what highlights are spectacular
Canon already does this (to some degree) with the mode 'highlight tone priority'. This is a genuinely under used mode that seeks to place emphasis on preservation of highlight detail. Only available on a 1DSMKIII at ISO200. Not sure if its available on other models (I think it is). http://www.luminous-landscape.com/forum/index.php?topic=20984
-
For low contrast subjects I'd suggest that exposing for mid gray would give good enough image quality, even if we could improve the image quality somewhat by exposing fully to the right.
Exactly, or rather... depending on the capability of the specific sensor, if the scene/subject is suffice within what we judge as the "quality zone" within the limits of DR, then there seem little point in ETTR.
In such cases it seems we are back to exposing for averaged mid tone... :)
-
True, but with a 1 degree spot meter you have to find the brightest area of the subject where you want highlight detail and then increase exposure by about 2.5 stops as Bruce Fraser suggested years ago.
But wouldn't that be completely blown when aiming at something colored?
Be it based on a matrix exposure sensor or a liveview reading, I'd think ETTR automation is way easier that smile recognition implemented in many P&S.
Canon already does this (to some degree) with the mode 'highlight tone priority'.
??? HTP is only an underexposure (http://forums.adobe.com/message/1384329#1384329) (and then, a curve applied in post by DPP or LR as well)... Nor much to do with specular highlight detection as far as I can understand?
-
Same as Ansel we also need to know what is critical for our exposure for the specific media we use, thus in our case how much above neutral is the bright point, and which is not dependent on Bruce Fraser's recommendation of 2.5 stops but on the performance of the specific sensor in our camera. Thus we need test sensor for this in order to be assertive.
That is correct. The 2.5 stops comes from the fact that white is about 2.5 stops from 18% (log2 [1/0.18] = 2.47). Many cameras allow 0.5 EV headroom for the highlights, so you would have to add 3 EV for a totally ETTR exposure. All one has to do is expose a gray card (or other uniform surface--white is OK) and determine the resulting raw value in the green channel of the raw file (Iris, DCRaw, or Rawnayze can do the job) and calculate the percent saturation of the sensor. Green is used, since the white balance multiplier is 1.0, but less for the red and blue channels.
Regards,
Bill
-
That is correct. The 2.5 stops comes from the fact that white is about 2.5 stops from 18% (log2 [1/0.18] = 2.47).
And yet, at least when I shoot such a subject, I can open up beyond that another stop, stop and a half without blowing the highlights and normalizing using Exposure in ACR/LR.
If I take an incident reading, same deal. I can open up 1.5 stops over its recommendation and ETTR. So where’s the disconnect here between using a meter as we’ve done for years (and getting proper exposure, for lets say chrome) and finding that these recommendations do not provide optimal exposure for the raw?
-
And yet, at least when I shoot such a subject, I can open up beyond that another stop, stop and a half without blowing the highlights and normalizing using Exposure in ACR/LR.
If I take an incident reading, same deal. I can open up 1.5 stops over its recommendation and ETTR. So where’s the disconnect here between using a meter as we’ve done for years (and getting proper exposure, for lets say chrome) and finding that these recommendations do not provide optimal exposure for the raw?
That's a good question. The Kodak Q14 reflection gray scale is useful here. This image is a photograph exposed so that Patch M has a sensor saturation of 18%, which corresponds to a pixel value of 116 in sRGB. Patch A has a density of 0.05 or about 90% reflectance and gives an sRGB value of about 242. This is about the maximum that can be achieved on a paper target (the Babel reflector (http://www.babelcolor.com/main_level/White_Target.htm) has a reflectance of 99% and is an ideal white target, but is rather expensive and is also small).
(http://bjanes.smugmug.com/Photography/Exposure-1/i-HGc6MCn/0/O/q14gray18.png)
The chart shown below was inspired by a post by Julia Borg which does not seem to be currently online. It shows the density of the patches along with the reflectance and exposure correction needed to place an exposure meter reading at a given luminance. Values for both 18% and 12% meter calibrations are shown, and corresponding pixel values for gamma 1.0, 1.8, and 2.2 are also shown.
(http://bjanes.smugmug.com/Photography/Exposure-1/i-qV5r3Mb/0/O/BorgCalculations.png)
Objects with a reflectance greater than 90% are unlikely to be observed in non-specular images in a natural scene, so one could place the luminance for a reflectance of 98% (100% can't be shown as density, which is a log scale). The chart shows the exposure compensation needed to place the reading at a given pixel value. For an 12% meter (used by the Nikon D3 and many other cameras), you would need +3 1/8 EV to place the reading at a pixel value in sRGB of 252 in a gamma 2.2 encoded space. What you need for your camera depends on its calibration.
Regards,
Bill
-
The two threads generated by the original exceptionally lucid article are more interesting than anything I've previously read on ETTR. I understand the issues in a general way however I wouldn't pretend to be able to contribute other than anecdotally. Many thoughts arise, however the two of mine that immediately surface are:
What are the histograms in View NX and Capture NX2 derived from (when viewing in RAW mode)?
In the other thread it's asserted that for a D3 (I use a D700 predominantly) there's little point in using ISO values >800 - it's better to push in post. I'm aware that there are also variables related to the contrast range in the scene, however that was the generalisation that I came away with. This seems to fly in the face of the near-universal assumption (even if not thereby validated!) that this range of sensors is notable for high-ISO performance. I'm here relating this to RAW shooting, rather than JPEGS, which may even be what most people usually shoot.
I was prompted to take a look at some exterior shots that were accidentally over exposed to a degree that I'd considered them write-offs; I'd previously been shooting HDR bracketed interiors. Amazingly NX2, which is restricted to +/- 2 stops exposure compensation, pulled back the building at -2 to an acceptable exposure: the overcast sky was still blown however. I was very surprised indeed.
Now when shooting outside on even fairly bright days I've always tended to use a little -ve compensation, particularly with matrix metering, as I hate blown out looking clouds and I've always tended to use "highlight protection" in NX2 conversions ras opposed to -ve exposure compensation followed by "shadow protection" to raise the shadows. Now I'm wondering if my approach has been fundamentally wrong even though I've usually been broadly satisfied with the results.
Hmm...
Roy
-
Michael,
while i commend your reiterated plea for a new exposure paradigm for digital i still do not see this happening. The first generations of digital cameras were designed to encourage film photographers to switch and therefore they pretended exposing digital was just like film. And current designs continue this since the companies do not want to alienate their customers by telling them now things have changed. What i do see happening is a quite, invisible change to ETTR in cameras without RAW output. Maybe this is already in progress - there is no way to tell without a direct comparison or raw output. I would be very happy to be proven wrong of course.
I think you should be careful when dismissing technical arguments concerning your text on the basis of the perceived credentials of the one bringing then up though. I don't want to participate in the technical argument here but ideas should be judged by their own merit, not by the merit of the one who states them. This is especially important here i think since you also criticize an established opinion (which is also still taught in lots of books and schools by people with widely recognized credentials).
-
In the other thread it's asserted that for a D3 (I use a D700 predominantly) there's little point in using ISO values >800 - it's better to push in post. I'm aware that there are also variables related to the contrast range in the scene, however that was the generalisation that I came away with. This seems to fly in the face of the near-universal assumption (even if not thereby validated!) that this range of sensors is notable for high-ISO performance. I'm here relating this to RAW shooting, rather than JPEGS, which may even be what most people usually shoot.
Roy
Roy,
For a detailed explanation of how to read DXO dynamic range graphs and how to use them for exposure decisions, see this post (http://www.luminous-landscape.com/forum/index.php?topic=42158.msg352373#msg352373) by Emil Martinec. You might also enjoy reading Emil's post on Signal to Noise and Exposure Decisions (http://theory.uchicago.edu/~ejm/pix/20d/tests/noise/noise-p3.html#ETTR), which discusses ETTR and Michael's erroneous statements about the number of levels in the brightest f/stop of a 12 bit digital capture by current sensors.
Regards,
Bill
-
As Nicolas (NikoJorj) implied with his comment 'But wouldn't that be completely blown when aiming at something colored?' the various posts suggesting using spot-meters completely miss the fact that this would not address the problem of blowing out an individual channel.
The automatic ETTR system proposed by Michael has a huge advantage in that it would separately address the exposures for each of the RGB channels of the sensor and select an ETTR exposure that would maximise the exposure in one or more of the channels. If the area giving this exposure is near neutral in colour, this is likely to be similar to the exposure that could be calculated using a spot-meter (having previously determined the compensation needed to produce near saturation). However, if the area giving the individual channel ETTR exposure is a saturated colour, the exposure is likely to be very different from that obtained using a spot-meter.
The suggestion of using a multi-segment meter such as the sensor used for matrix metering would probably also have the same problem as using a spot-meter (unless it was able to separately measure RGB channels, with similar spectral sensitivity to the imaging sensor).
It would obviously be possible, but usually impractical, to use coloured filters with a spot-meter (with appropriate spectral characteristics and individual correction factors) to determine individual channel ETTR exposures and then set the lowest of the three exposures.
An additional advantage of the system proposed by Michael is that it could also be applied to those sensors that use more than three colours (I can't remember which manufacturer it is who has green and blue-green filters for the two green pixels in the Bayer pattern) since it would be applied to the individual channels prior to the demosaicing and conversion to a conventional RGB image.
Regards
Nigel
-
One can use the dynamic range vs ISO plot on DXO to determine this point of diminishing returns. When the curve becomes linear, increasing ISO will have minimal effect on read noise. As shown on the plot below, this occurs at about a measured ISO of 700 for the Nikon D3 (the ISO indicated by the camera will be higher with this camera). With this camera there is really no point in increasing the ISO above 800, since you will only decrease highlight head room. Expose as much as possible at a camera ISO of 800 and use the raw converter to increase exposure.
With the D7000, the curve is linear from base ISO and there is no real need to increase the ISO to obtain a "better" histogram. One can expose as much as conditions allow and make up the difference in the raw converter. The appearance of the histogram is irrelevant. The scientific explanation for these considerations is given by Emil Martinec (http://theory.uchicago.edu/~ejm/pix/20d/tests/noise/noise-p3.html#ETTR). The article was written before the D7000 was available.
Bill,
It is not clear to me if you are saying that the D7000 or the D3 is the better sensor.
My initial thought would be that I would rather be able to increase ISO, with less increase in noise....even if it were not the entire range of ISOs available.
Thanks, John
-
However, if the area giving the individual channel ETTR exposure is a saturated colour, the exposure is likely to be very different from that obtained using a spot-meter.
A spot meter will measure any individual RGB value or combination thereof as plain tonal values. Thus we need to be aware also of zones 0, I or II (around saturation point) for the individual RGB colors.
-
Hi,
The D7000 has better dynamic range at minimum ISO. If it is the best sensor depends on your needs. For high ISO work the D3 is probably better. If you need good shadow detail at low ISO the D7000 would be a better choice.
The major differences is that the D3 sensor is bigger, so it collects more photons. It may also have better quantum efficiency or less sharp color grid array. On the other hand the Nikon D7000 has a better signal processing path. So D7000 picks up less noise in the shadows. Noise in midtone will be mostly affected by "shot noise" which is linked with the number of photons captured, putting the D3 to advantage.
The D3 needs 50% less enlargement than the D7000 for a given print size, which means that it has lower demands on the lens. Another way of saying this is that it will transfer more contrast on fine detail than the smaller sensor camera.
The best camera is probably the D3X, which has very similar characteristics to the D7000 but having a larger and more high resolving sensor. For high ISO shooting the D3S may be better.
I include "Density Range" and "Tonality Range" plots from DxO for the D7000, D3 and D3S. Density range is essentially looking at shadow noise, while "Tonality Range" is more like how smooth midtones will be.
Discussing the "best camera" needs to relate to requirements but also to cost. What do you need and what you are willing to pay? The situation may be different if you acquire a new set of tools or if you are adding to an existing one? Let's assume that your favorite is a 24-70/2.8. It would have a field of view of 36-105 lens on a D7000, perhaps not you would regard to be optimal. On the other hand, Nikons 16-85/3.5-5.6 may be a decent standard zoom for the D7000, but not the lens for low light shooting.
Best regards
Erik
Bill,
It is not clear to me if you are saying that the D7000 or the D3 is the better sensor.
My initial thought would be that I would rather be able to increase ISO, with less increase in noise....even if it were not the entire range of ISOs available.
Thanks, John
-
Hi,
I see some more complexity. The raw image will contain three color signals with luminance probably corresponding to the spot meter. Color balance is applied in post processing and the question is also how that processing is done? The raw signal will probably contain at most 14-bits except those MFDBs having 16 bit signals. Raw conversion is probably done in 16 bit. If we assume that raw conversion would be done in low bits we would have a headroom of 2 bits (that is two stops) for handling color balance without clipping.
Best regards
Erik
A spot meter will measure any individual RGB value or combination thereof as plain tonal values. Thus we need to be aware also of zones 0, I or II (around saturation point) for the individual RGB colors.
-
I see some more complexity. The raw image will contain three color signals with luminance probably corresponding to the spot meter. Color balance is applied in post processing and the question is also how that processing is done? The raw signal will probably contain at most 14-bits except those MFDBs having 16 bit signals. Raw conversion is probably done in 16 bit. If we assume that raw conversion would be done in low bits we would have a headroom of 2 bits (that is two stops) for handling color balance without clipping.
The data we can retrieve (find useful) in post and which corresponds to our choice of zone 0, I or II as "bright point tool" is important (before and/or after recovery is our own preference). That does not limit to doing so mere for a neutral bright point, does it? ;)
-
Hi,
The data are scaled when doing white balance. So data that is unclipped in the raw file can be clipped when doing white balance.
Best regards
Erik
The data we can retrieve (find useful) in post and which corresponds to our choice of zone 0, I or II as "bright point tool" is important (before and/or after recovery is our own preference). That does not limit to doing so mere for a neutral bright point, does it? ;)
-
After having read through the article and now through this thread (which was interesting, otherwise I wouldn´have spent that much time!) some thoughts come to my mind:
1.: Usability of the exposure concept
it is agreed that using all space on the histogram- with a preferrence to "expose to the right" is a valuable and useful method to achive optimum SNR.
The problem is only that scene lighting changes, sometimes rapidly. If an automatic process is not able to prevent full clipping (full loss of information - whereas using the histogram fully is also not "linear" so there are parts of the available steps lost when doing this which can be overall usefull as dicussed here ) then I think it is more useful to compromise and give it a certain amount of reserve.
2.: Performance of differing Chip Concepts in comparison
As we have heard the channels do not react the same, further it may push the Dynamic range to a limit using it fully. How is a concept like Foveon reacting on these finetunings -and -
wouldn´t it be better if a chip was made which sacrifices the luther condition but instead collects SNR by all available tricks for the channels and then postprocess (either by firmware or in the Rawconverter), something like Fuji made with the 2 different sizes of pixel onchip to improve dynamic range or maybe using other color schemes (also Fuji Hexagon "EXR") or maybe going a step further (and more crazy costwise) - why not using a 3 chip concept as it is in Video cameras but for Photography purposes (using differing sensitivities for the channels or differing exposure times-or even better using differently sensible silicon for each channel ?) ? Wouldn´t this eliminate the need of about any of these discussions and maybe there is a way to use this in future cameras ( Imagine a cheap and small sensor highspeed 3Chip video camera using superexposure and future incamera processing power to resolve high resolution in variable resolutions together with variable sharpness like the Lytro camera....?!)
I´d be interested to hear how the forum people would sort these thoughts to this thread.
TIA and greetings from Munich
Stefan Steib - HCam.de
-
1.: Usability of the exposure concept
For me, that's exactly Michael's point : for now, we must rely on Ruth-Goldbergesque contraptions to be able to achieve ETTR (and the number of threads about UniWB, and the number of people willing to stand the horrendous green previews it gives, could be a reasonable proof that this is not exactly a small niche need), but a simple firmware upgrade (at least on cameras with live view) could probably give us a much more accurate automated exposure, for those times when we don't have time to fiddle with trial-and-error and still need an optimal capture to maximise DR.
2.: Performance of differing Chip Concepts in comparison
Ach, diese Bayerischen (http://www.pumuckl.de/), die sind immer nach alles komplizieren und... Ooops, sorry, I think I have eaten one too many Prussians at breakfast today. :-[ ;)
For me, what works, works ; and for my need of wide dynamic range (the classical landscape need of bright cloudy sky and darker land beneath) a Bayer sensor the thing that works, ie the better compromise. It just would be even better with an ETTR expoosure mode and a raw histogram. ;D
If you got some spare time, the strength and weaknesses of Foveon sensors are abundantly exposed in this thread (http://www.luminous-landscape.com/forum/index.php?topic=55952.0) (and ETTR and raw histograms would also be very useful for those, because they have less total DR and still give WB-corrected and tone-corrected jpeg previews - and histograms AFAIK).
-
It always amazes / annoys / amuses me when I publish an article that has been painstaking peer-reviewed by some of the brightest minds in the industry – people who design sensors and write raw software (in this instances) and then "experts" whose credentials are unknown tell me (us) why the information in the article is wrong.
Michael, those brightest minds in the industry came to tell you what you could have read from your own forum's "experts" more than two years ago. The questions exposed in your article were already discussed here:
Camera manufacturers PLEASE: when RAW histograms and an ETTR mode? (http://www.luminous-landscape.com/forum/index.php?topic=33267).
The no-reason for not having an automated ETTR mode in a digital camera, a user setting indicating % of allowed clipped pixels, RAW-based histograms and clipping warnings,...
PS: 2^12=4.096, not 4.098
-
Hi,
The data are scaled when doing white balance. So data that is unclipped in the raw file can be clipped when doing white balance.
Best regards
Erik
Quite true, but one can handle clipping with white balance by setting the white balance multipliers all less than or equal to one. Guillermo Luijk explains this topic quite well in his DCRaw tutorial (http://www.guillermoluijk.com/tutorial/dcraw/index_en.htm)--see the section on white balance.
As en example, here are actual camera histograms taken from the Nikon D3 of a saturated yellow flower. The camera was set to Adobe RGB, the widest space available on the camera. Shot 10 was at the exposure indicated by the meter, but I saw clipping in the red and green channels, so I reduced exposure until the green no longer clipped (shot 12). Note that the luminance histogram (black and white) shows no clipping. See below for an explanation.
(http://bjanes.smugmug.com/Photography/ETTRColor/LCDcomposite/319807719_Km7uz-O.jpg)
The Rawnalize histogram of image 10 shows that the red and green channels are just at clipping, but the red channel will be strongly clipped when white balance is applied (the red white balance multiplier is about 1.5).
(http://bjanes.smugmug.com/Photography/ETTRColor/010Photobola/319807614_3NUTu-L.png)
In shot 12, the red and green channel is about 0.3 EV below clipping and the green channel about 0.5 EV below clipping. The camera histogram clipping is likely due to saturation clipping in AdobeRGB, the color space of the preview. Unfortunately, ProPhotoRGB is not available with this camera (or any other cameras I know about).
(http://bjanes.smugmug.com/Photography/ETTRColor/012Photobola/319807662_fe5WM-L.png)
ACR will not allow setting the WB multipliers all <= 1, but one can reduce the exposure to achieve this effect and use ProPhotoRGB to reduce saturation clipping. I allowed slight clipping of the red channel and increased brightness to give a better appearance.
(http://bjanes.smugmug.com/Photography/ETTRColor/i-w84vPW6/0/L/Img10MinusExp-L.png)
Finally, one should note that luminance histograms displayed by the camera black and white histogram may not show clipping when it is present in the color channels. This is because the luminance histogram looks at all pixels but does not keep track of their location in the image. This is well demonstrated in the Cambridge in Color tutorial (http://www.cambridgeincolour.com/tutorials/histograms2.htm) on histograms.
Here is the Photoshop luminance histogram and the color histograms of the same image. Note that the luminance histogram shows no clipping, but clipping is present in the red channel. One can get a better estimation of the color channels by using UniWB, but saturation clipping can still occur in the AdobeRGB space used for the camera color histogram. I don't usually use UniWB do keep it in one of the data banks of my camera, so I can use it when needed. Modern cameras are good enough that slight underexposure (short of ETTR) can be tolerated. Remember that SNR increases as the square root of exposure, so doubling of the exposure increases the SNR only by a factor of 1.4. Raw histograms would be nice, but one can still get good results with the available tools if you know how to use them.
(http://bjanes.smugmug.com/Photography/ETTRColor/i-jJJBpVJ/0/L/PhotoshopHistogramsImg12-L.png)
Regards,
Bill
-
I had the chance to try out what was the main thrust of the essay. For a high contrast scene I use the digital zone method which I will keep using but on a lower contrast scene which imo falls within the dynamic range of a scene I used centre weight and raised the EV on some scenes by 1.0 and 1.3 above what I would normally shoot. Imported them into ACR and I had the flashing red overlay on a lot of highlights which would normally horrify me. Lowered the exposure slider which was about -1 and then processed in my normal manner and liked what I saw. In one particular scene I had auto bracketed it on the camera using + 1.0, two shots. I processed both. One didn't have the flashing red and the other had to be lowered by -1 exposure. Processed both and used the side by side method in Photoshop to compare them and they looked very similar. The +1 had lighter dark areas to begin with which was the object of the exercise. The overexposed areas which I feared burnt out initially weren't once the exposure was lowered. I will definitely try again on a suitable day and so far my verdict is .... worth trying. :)
-
Hi,
The data are scaled when doing white balance. So data that is unclipped in the raw file can be clipped when doing white balance.
Best regards
Erik
Erik,
You make a valuable point. However if WB does not change by much, can we assume there will not be much influence?
On another note, in above I misstaken referred bright point to around zone 0, I, II , instead should be VIII, IX, X, sorry about that.
Regards
Anders
-
Anders,
I don't know! What happens is that the channels are shifted quite a lot in postprocessing . To achieve correct white balance, multipliers are applied to each channel. Which multipliers depend on color temperature. These things can be checked out using DxO data and perhaps using "raw-analyzer". I have not really done that, because I presume that it is easy to draw false conclusions.
Much may also depend on raw processor. They may have different strategies, algorithms and priorities.
Best regards
Erik
Erik,
You make a valuable point. However if WB does not change by much, can we assume there will not be much influence?
On another note, in above I misstaken referred bright point to around zone 0, I, II , instead should be VIII, IX, X, sorry about that.
Regards
Anders
-
I have read through this thread (although my eyes began to glaze over with some of the technical stuff ;D) and apologize if I missed this point. There is a bit of a discussion on another site about the use of ETTR for a jpeg image (especially in light of Michael's comment under the "Caveat" heading). Can anyone advise if ETTR is raw-specific or if there is any benefit at all to ETTR for a jpeg file?
Thanks,
Marv
-
Can anyone advise if ETTR is raw-specific or if there is any benefit at all to ETTR for a jpeg file?
ETTR means post processing (exposure correction)
JPEG is a finished output format, never intended for post processing
So conceptually JPEG-ETTRing is crazy.
-
ETTR works based on the linear behavior of digital sensors and corresponding RAW files
Jpegs are far from linear (gamma encoded, color space encoded, white balanced, to name a few)
The best you could do with Jpegs is to aim for precise exposure and correct white balance, not needing post processing, just as Guillermo said.
-
As en example, here are actual camera histograms taken from the Nikon D3 of a saturated yellow flower. The camera was set to Adobe RGB, the widest space available on the camera. Shot 10 was at the exposure indicated by the meter, but I saw clipping in the red and green channels, so I reduced exposure until the green no longer clipped (shot 12). Note that the luminance histogram (black and white) shows no clipping. See below for an explanation.
(http://bjanes.smugmug.com/Photography/ETTRColor/LCDcomposite/319807719_Km7uz-O.jpg)
The Rawnalize histogram of image 10 shows that the red and green channels are just at clipping, but the red channel will be strongly clipped when white balance is applied (the red white balance multiplier is about 1.5).
(http://bjanes.smugmug.com/Photography/ETTRColor/010Photobola/319807614_3NUTu-L.png)
...
ACR will not allow setting the WB multipliers all <= 1, but one can reduce the exposure to achieve this effect and use ProPhotoRGB to reduce saturation clipping. I allowed slight clipping of the red channel and increased brightness to give a better appearance.
(http://bjanes.smugmug.com/Photography/ETTRColor/i-w84vPW6/0/L/Img10MinusExp-L.png)
Finally, one should note that luminance histograms displayed by the camera black and white histogram may not show clipping when it is present in the color channels. This is because the luminance histogram looks at all pixels but does not keep track of their location in the image. This is well demonstrated in the Cambridge in Color tutorial (http://www.cambridgeincolour.com/tutorials/histograms2.htm) on histograms.
... One can get a better estimation of the color channels by using UniWB, but saturation clipping can still occur in the AdobeRGB space used for the camera color histogram. I don't usually use UniWB do keep it in one of the data banks of my camera, so I can use it when needed. Modern cameras are good enough that slight underexposure (short of ETTR) can be tolerated. Remember that SNR increases as the square root of exposure, so doubling of the exposure increases the SNR only by a factor of 1.4.
Raw histograms would be nice, but one can still get good results with the available tools if you know how to use them.
Interesting example, Bill.
So the reduction of exposure was not necessary
while the initial shot # 10 was already quite well exposed (to the right) – if I get you right.
First, the single R/G/B camera histograms may suggest a bunch of clipping due single channel "amplifications" resulting from in-camera processing i.e. white balance and saturation clipping, but then all of this is "averaged" with the luminance histogram - which finally correlates with the results from Rawnalize (no relevant clipping).
Peter
--
-
Interesting example, Bill.
So the reduction of exposure was not necessary
while the initial shot # 10 was already quite well exposed (to the right) – if I get you right.
First, the single R/G/B camera histograms may suggest a bunch of clipping due single channel "amplifications" resulting from in-camera processing i.e. white balance and saturation clipping, but then all of this is "averaged" with the luminance histogram - which finally correlates with the results from Rawnalize (no relevant clipping).
Yes, that is how I interpret the situation. The clipping of the color histograms occurred with white balance. UniWB would give a more accurate RGB histogram, but the color space would still be AdobeRGB with this camera.
Regards,
Bill
-
Quite true, but one can handle clipping with white balance by setting the white balance multipliers all less than or equal to one. Guillermo Luijk explains this topic quite well in his DCRaw tutorial (http://www.guillermoluijk.com/tutorial/dcraw/index_en.htm)--see the section on white balance.
This method will not always work. Suppose the WB multiplier on the R,G,B channels are 2.0,1.0,1.0. We could normalize so that they are 1.0,0.5,0.5, but now suppose there is a clipped green patch that should have been at 1.5 times the clipping point of the raw data; it will register as 0.5 times the clipping point after the normalization when it should have been 0.75.
-
This method will not always work. Suppose the WB multiplier on the R,G,B channels are 2.0,1.0,1.0. We could normalize so that they are 1.0,0.5,0.5, but now suppose there is a clipped green patch that should have been at 1.5 times the clipping point of the raw data; it will register as 0.5 times the clipping point after the normalization when it should have been 0.75.
That is the challenge for realistic HL recovery routines, but your example involves a clipped (Green) channel, not a proper ETTR situation. A proper ETTR image can be White Balanced without loss of highlight accuracy by using a proper scaling of all 3 channels in linear gamma space.
Besides allowing the user a manual control over the assumed true level of the clipped pixels, one could employ various heuristics for making an educated guess. Part of the heuristics could be an assumption of common differences in WB scaling factor in other parts of the image that have slightly lower average luminosity level. Areas with presumed (e.g. with an assumed D50 illuminant) neutral color should have higher weighting. Another assumption could be used for clipped specular highlights. Specular highlights often also have a high spatial frequency and could be treated as a special case of mostly reflecting the illuminant's color and a bit of their own color. A high pass filter combined with a high luminosity threshold could be used to select such areas.
Cheers,
Bart
-
Exactly. Once any significant non-linearity has been introduced into the system (and clipping is certainly a big one!), then clearly a simple linear operator like white balance is no longer correct. (This is why it's hard to apply white balance correctly to JPEGs. They have undergone potentially many non-linearities already in their processing.)
-
Is there any benefit at all to ETTR for a jpeg file?
Yes, but only if you correct the brightness in-camera before the JPEG is written. For example, if you are shooting a JPEG at ISO 100 and notice that you have 1 stop of unused highlight headroom, your camera might have an "ISO 50" (or "L") mode which is really just a digital "-1 EC" behind the scenes (in the camera). If so, you can enable that to get the benefits of ETTR in your JPEG.
-
"Expose to right, it is as simple as that?"
No, it isn't.
Agree with the conclusion, we should to expose to the right and the cameras should support this.
No, they shouldn't. Cameras must not try to be smarter than photographers ... at least photographer's cameras shouldn't. Exposing To The Right (or, as we used to say in the pre-digital era, exposing for the highlights) is the right thing to do when the subject's dynamic range is about equal to or moderately greater than the dynamic range the camera can handle—usually. Exceptions can, and will, happen. And it usually is not the right thing to do when the subject's dynamic range is significantly smaller or vastly greater than what the camera can handle. So no, it's not as simple as that.
People bluntly advocating ETTR usually are ignoring two things. First, some highlights are not worth preserving—but it's you who's got to decide, not the camera. Second, ETTR will optimize separation of tones but sacrifice separation of colours. So if the subject's dynamic range is small then don't push it up all the way to the right. Instead, leave it centered ... or push it up half-way between center and right.
... if you are shooting a low-contrast scene, using your exposure meter and centering the image data in the center of the histogram is a suboptimal idea ...
No, that's not necessarily true. For the optimal exposure, you'd need to balance dynamic range versus colour range. Where the best balance is depends on your image content. If you plan to convert your capture to black-and-white then by all means push the tones as far to the right as you possibly can. But when you plan to capture a wide range of pastel and saturated colours then better back off a little.
That's why an automatic ETTR exposure mode would make a lot less sense than most people think. There are situations where it would be useful, but then there others where it's not.
-
Exposing To The Right (or, as we used to say in the pre-digital era, exposing for the highlights) is the right thing to do when the subject's dynamic range is about equal to or moderately greater than the dynamic range the camera can handle—usually. Exceptions can, and will, happen. And it usually is not the right thing to do when the subject's dynamic range is significantly smaller or vastly greater than what the camera can handle. So no, it's not as simple as that.
I dont understand the last sentence. Scenes of low dynamic range woud be candidates for "ETTR" in my book.
People bluntly advocating ETTR usually are ignoring two things. First, some highlights are not worth preserving—but it's you who's got to decide, not the camera. Second, ETTR will optimize separation of tones but sacrifice separation of colours. So if the subject's dynamic range is small then don't push it up all the way to the right. Instead, leave it centered ... or push it up half-way between center and right.
What do you mean by "separation of colors"?
That's why an automatic ETTR exposure mode would make a lot less sense than most people think. There are situations where it would be useful, but then there others where it's not.
What is usually requested is for cameras to provide better feedback in order for the photographer to do the right choices wrgt exposure - for instance ETTR if that is deemed appropriate.
-h
-
Hi,
ETTR is about optimizing dynamic range. The inclusion/exclusion of highlights is not a part of ETTR. ETTR essentially says that it is preferable to maximize the number of photons detected by the sensor.
I have not seen any evidence that color separation would be affectedby ETTR, on contrary, noise may reduce color separation and ETTR minimizes noise (it is all it does). Actually it does not minimize noise but maximizes signal to noise ratio, to be correct.
Color separation is in my view only a function of the spectral charectiristics of the color grid array and the color transformation matrix, both of which are independent of exposure.
Best regards
Erik
People bluntly advocating ETTR usually are ignoring two things. First, some highlights are not worth preserving—but it's you who's got to decide, not the camera. Second, ETTR will optimize separation of tones but sacrifice separation of colours. So if the subject's dynamic range is small then don't push it up all the way to the right. Instead, leave it centered ... or push it up half-way between center and right.
No, that's not necessarily true. For the optimal exposure, you'd need to balance dynamic range versus colour range. Where the best balance is depends on your image content. If you plan to convert your capture to black-and-white then by all means push the tones as far to the right as you possibly can. But when you plan to capture a wide range of pastel and saturated colours then better back off a little.
That's why an automatic ETTR exposure mode would make a lot less sense than most people think. There are situations where it would be useful, but then there others where it's not.
-
Second, ETTR will optimize separation of tones but sacrifice separation of colours.
Could you elaborate a bit on that? I am not sure I understand.
No, that's not necessarily true. For the optimal exposure, you'd need to balance dynamic range versus colour range. Where the best balance is depends on your image content. If you plan to convert your capture to black-and-white then by all means push the tones as far to the right as you possibly can. But when you plan to capture a wide range of pastel and saturated colours then better back off a little.
You seem to imply increasing dynamic range hurts color range. By which mechanism? ETTR doesn't inherently increase the dynamic range of a system, it just exploits it optimally. If the captured scene has too much dynamic range for your taste, nothing prevents you from post-processing to limit it. OTOH, if you haven't captured enough of the DR of a scene, there's no way to get it back after the capture. This being said, although your suggestion is a bit imprecise, I don't dismiss it since "ETTR to the max" could very well end up on the upper non-linear response zone of the sensor.
-
The inclusion/exclusion of highlights is not a part of ETTR.
Sure it is. As a matter of fact, including highlightsand not excluding them is the essence of ETTR. That's where ETTR got its name from.
ETTR essentially says that it is preferable to maximize the number of photons detected by the sensor.
You really want to recapitulate what ETTR actually is. Hint: Maximizing the number of photons detected by the sensor it is not. After all, a capture over-exposed by several f-stops will always detect far more photons than a properly exposed one.
... and ETTR minimizes noise (it is all it does).
Well, that's my point—it is not all it does.
Color separation is in my view only a function of the spectral charectiristics of the color grid array and the color transformation matrix, both of which are independent of exposure.
Your view is wrong.
Simply consider the extremes. The blackest black that an RGB image can produce is RGB(0, 0, 0). No colour separation at all; one colour only at this tone level: black. The same at RGB(255, 255, 255)—only one single colour, white, at the maximum tone level; no variations possible (that's for 8 bits per RGB channel—for higher bit depths adjust the numbers accordingly but the principle will remain the same). The most saturated red, for example, would be RGB(255, 0, 0)—that's a tone much brighter than black but also much darker than white. Colours that are as bright as RGB(255, 255, 255) but at the same time as saturated as RGB(255, 0, 0) simply cannot exist in an RGB system where each channel's range of values is finite. So the variation of possible colours is widest at medium tone levels and narrowest at extremely low or extremely high tone levels. To complicate matters even more, RGB(0, 255, 0) is not the same brightness level as RGB(255, 0, 0), and RGB(0, 0, 255) is yet another brightness level.
Of course, things still aren't as simple as that. First, you're right when you're saying that noise will hurt colour separation, so avoiding noise basically is a good thing. That's why I said, put your histogram's peak half-way between center and right when subject contrast permits and colours are important. Second, a camera's RGB channels usually won't clip all at the same brightness level—that further complicates matters and is another reason not to push your histogram to the farthest right when you don't have to.
So—ETTR sure is a useful rule of thumb generally but still needs some consideration. It is not the gold standard for all situations and circumstances. In most cases ETTR is a good idea but sometimes you must expose beyond ETTR, and sometimes it's better to back off from ETTR by one stop or two. It's just the same as everywhere else in real life: Simple rules aren't.
-
The blackest black that an RGB image can produce is RGB(0, 0, 0). No colour separation at all; one colour only at this tone level: black. The same at RGB(255, 255, 255)—only one single colour, white, at the maximum tone level; no variations possible
…and RGB(113, 115,29) is just a single color too—so no variation is possible. Still not sure what you mean by color separation. Naturally, with a single color, whether it's pure black, white, or any other has no variation by definition, that's obvious. Color variation, or separation, or whatever you're calling it doesn't make any sense until you are speaking of more than one color. Since the sensor is capturing linear data, it shouldn't degrade as you push it to the right until you start clipping. Are you just explaining the long way not to clip individual channels?
-
Hi,
There has been a lot of dicussion about this and it seems that there is no consensus about it. I got the impression that most color cast observed comes from clipping one or more of the RGB channels. Another impression I got is that sensors are seen as mostly linear devices. On the other hand it may be that sensors have some kind of shoulder, too. This may also depend on the make of sensor. A shoulder would introduce some color shift.
The included density plot of a 41 step wedge doesn't show much of a shoulder. The photo was made on a simple lightboard so some unlinearity may come from illumination rather than from sensor/wedge.
Another view may be that todays sensors are so good that noise seldom is a large problem at base ISO, so the need to keep noise down may be less important. On the other hand, exposing to the right is the only way of keeping maximal shadow detail. Overdo it and there will be clipping.
Best regards
Erik
This being said, although your suggestion is a bit imprecise, I don't dismiss it since "ETTR to the max" could very well end up on the upper non-linear response zone of the sensor.
-
Colors is absolutely not a problem with ETTR as long as you have not clipped the raw channels. If you have clipped a raw channel (any one, or multiple ones) in an area of the image that you care about, then all bets are off.
-
Your view is wrong.
Simply consider the extremes. The blackest black that an RGB image can produce is RGB(0, 0, 0). No colour separation at all; one colour only at this tone level: black. The same at RGB(255, 255, 255)—only one single colour, white, at the maximum tone level; no variations possible (that's for 8 bits per RGB channel—for higher bit depths adjust the numbers accordingly but the principle will remain the same). The most saturated red, for example, would be RGB(255, 0, 0)—that's a tone much brighter than black but also much darker than white. Colours that are as bright as RGB(255, 255, 255) but at the same time as saturated as RGB(255, 0, 0) simply cannot exist in an RGB system where each channel's range of values is finite. So the variation of possible colours is widest at medium tone levels and narrowest at extremely low or extremely high tone levels. To complicate matters even more, RGB(0, 255, 0) is not the same brightness level as RGB(255, 0, 0), and RGB(0, 0, 255) is yet another brightness level.
Actually, I think that your view is wrong. Can you provide us with images that support your controversial theory, or is it only based on thought-experiments? I think that the arguments presented above indicates that you should think things over once more.
If ETTR meant "expose the image as hot as possible", then you could hypothetically be right: if you manage to clip every single sensel, then all color information will be lost, and no highlight information will be present (in fact, no information will be present at all). I dont think that anyone is advocating such a practice, and if "ETTR guides" seems to indicate so, they may be poorly written.
The lesson that I take from ETTR is to expose as hot as possible _while_ avoiding clipping wherever I find it perceptually necessary. If bright, small highlights are uninteresting to me, then I will clip them (and both their brightness and color will suffer more or less as a consequence). If a larger bright patch is interesting to me (for instance, the sky), I will keep it within the linear region of my sensor, thereby no loss of "color separation" will occur in that part.
The consequence of separating "what exposure looks good on print, given an ideal camera" and "what exposure allows me to capture the stuff that I am interested in with the best possible precision" is that one can (if the situation allows) increase exposure somewhat, and have a better "desired signal"-to-noise ratio. After all, digital raw files can have their exposure adjusted for subjective targets after-hand, but adjusting the SNR after-hand is a lott harder.
-h
-
Your view is wrong.
Simply consider the extremes. The blackest black that an RGB image can produce is RGB(0, 0, 0). No colour separation at all; one colour only at this tone level: black. The same at RGB(255, 255, 255)—only one single colour, white, at the maximum tone level; no variations possible (that's for 8 bits per RGB channel—for higher bit depths adjust the numbers accordingly but the principle will remain the same). The most saturated red, for example, would be RGB(255, 0, 0)—that's a tone much brighter than black but also much darker than white. Colours that are as bright as RGB(255, 255, 255) but at the same time as saturated as RGB(255, 0, 0) simply cannot exist in an RGB system where each channel's range of values is finite.
Hi 01af,
As others have mentioned, your reasoning doesn't hold because the conceptual model is flawed. You are not alone, I've seen others with similar reasoning, so it's important to address and set straight. RGB(255,0,0) is by definition less bright (~22% Luminance) than RGB(255,255,255) is (100% Luminance), it's a different color.
You probably are thinking of the 3D hull representation of an RGB colorspace which seems narrower at the top and bottom of the 3D shape, but that is a transformation of the RGB coordinates into a colorspace where luminance is (more or less) separated from the chromaticity, while an RGB colorspace records coordinates in an orthogonal 3 axes system where luminance is not one of the axes.
With that hopefully out of the way, low contrast scenes are prime candidates for ETTR because S/N quality can be improved with minor risk of clipping highlights. Color gamut is not an issue, assuming the Raw converter doesn't introduce Hue-twists or unequal blackpoint clipping and such when pulling the exposure in postprocessing.
Cheers,
Bart
-
… and RGB(113, 115, 29) is just a single color too—so no variation is possible.
Are you trolling, or don't you understand the difference between colour and tone? There are no other RGB colours that are as bright as RGB(255, 255, 255)—but here are thousands of RGB colours that have the same brightness as RGB(113, 115, 29).
... because the conceptual model is flawed.
No, it's not.
RGB(255, 0, 0) is by definition less bright (~22 % luminance) than RGB(255, 255, 255) is (100 % luminance), it's a different color.
It is both a different colour and a different tone. There is only one RGB colour that has 100 % luminance but many thousands of RGB colours that have 22 % luminance (or any medium level of luminance). The closer the luminance level is to 0 % or 100 %, the smaller the number of RGB colours at that level of luminance is. Just how hard can it be to grasp this?
You probably are thinking of the 3D hull representation of an RGB colorspace which seems narrower at the top and bottom of the 3D shape ...
It doesn't just seem narrower at the top and bottom—it actually is narrower at the top and the bottom.
... but that is a transformation of the RGB coordinates into a colorspace where luminance is (more or less) separated from the chromaticity, while an RGB colorspace records coordinates in an orthogonal 3 axes system where luminance is not one of the axes.
You probably are thinking that hings are having either colour or luminance. However actually they always have both. In the orthogonal three-axes system—one axis for each of the three colour channels R, G, and B—the luminance axis basically is the space diagonal from the (0, 0, 0) corner to the (255, 255, 255) corner. And near the corners, the RGB colour space is pretty pointy.
-
complicate matters even more, RGB(0, 255, 0) is not the same brightness level as RGB(255, 0, 0), and RGB(0, 0, 255) is yet another brightness level.
OK - yes, we are aware of that. One shouldn't clip anything, everyone agrees. Yes, it can be difficult at times, everyone agrees and some have tried to develop methods to make sure clipping doesn't happen.
About linearity
There has been a lot of dicussion about this and it seems that there is no consensus about it.
Yes, I am afraid this is true. In scientific applications, the linearity of the sensor's response is important, analyzed, documented, etc... In cameras, whyen they don't use sensors that are available otherwise, there's essentially zero information available..
Edit: yes, your chart show a nice response linearity. Since all sensors (either CMOS or CCD) show a certain level of integral nonlinearity, I assume manufacturers take this into account and one shouldn't run into trouble. BTW, those discussions are always interesting in terms of personal education: since I try not to put my foot in my mouth too often (one can always hope ;)) I usually take the time to review the topic a bit before posting and have learned that in some applications, the variability of the non linearity over time leads to recalibration in some data acquisition protocols. Yet another fascinating example, with the one that Bart posted a while ago from the Dutch professor, that even when one thinks one knows something, there are always mountains of hidden things to learn!
-
You probably are thinking that hings are having either colour or luminance. However actually they always have both. In the orthogonal three-axes system—one axis for each of the three colour channels R, G, and B—the luminance axis basically is the space diagonal from the (0, 0, 0) corner to the (255, 255, 255) corner. And near the corners, the RGB colour space is pretty pointy.
Who is telling you that you have to expose any more than [255,0,0]*) when doing ETTR?
-h
*)no native sensor output looks like this, but I like your analogy to display-referred color spaces.
-
You probably are thinking that hings are having either colour or luminance. However actually they always have both. In the orthogonal three-axes system—one axis for each of the three colour channels R, G, and B—the luminance axis basically is the space diagonal from the (0, 0, 0) corner to the (255, 255, 255) corner. And near the corners, the RGB colour space is pretty pointy.
You know, you don't care about that. You've just a set of photon counters that return a bunch of numbers. ETTR is about getting the most accurate photon count (succintly the more you collect, the more precise your count is). Whether there is a blue, a green, a red, a SII an OIII, an Halpha filter in front, whether the data will be turned into a pretty picture, a graph, noise, an inverted pyramid or a purple icosahedron or whathever doesn't matter. Obfuscating the topic by taking those numbers and moving a level or three up the conceptual chain isn't helpful. The goal is "obtain the optimal initial numbers" then do whatever you want with them.
If you mean to say "we need to be careful when doing ETTR because we can eventually overflow a set of counters whithout overflowing others thereby creating a color/tone/accuracy/whatever issue", well, I guess everyone agrees and is aware of the issue.
-
There has been a lot of dicussion about this and it seems that there is no consensus about it.
I have two reasons to think my camera's sensor is very linear in the highlights and therefore colour shifts caused by ETTR are a myth. First beacuse I measured my camera's response, and only when some RAW channel gets clipped, the survivor(s) seems to have some non-linearity:
(http://www.guillermoluijk.com/article/anavsdig/curvaloglog350d.gif)
Second because I have fused dozens of images for HDR, and if exposure is matched correctly between differently exposed shots, the seams are totally invisible, even with zero transition (the transition happens when the RAW data coming from the most exposed shot gets closer to saturation than 0,15EV, and I arbitrarily chose that limit which could have even been higher).
Try to find any visible seam in the image on the left:
(http://www.guillermoluijk.com/tutorial/zeronoise/calculo.jpg)
So until someone comes to me with non-clipped RAW files displaying any colour shift, I'll stay thinking about it as a myth.
Regards
-
The closer the luminance level is to 0 % or 100 %, the smaller the number of RGB colours at that level of luminance is. Just how hard can it be to grasp this?
…
It doesn't just seem narrower at the top and bottom—it actually is narrower at the top and the bottom.
…
And near the corners, the RGB colour space is pretty pointy.
You're pretty mixed up here. And you are using the word luminance incorrectly—it is not the diagonal in an RGB cube, but that doesn't really matter because it's much simpler that you are making it.
Look, imagine a low contrast scene with RGB values between [100, 100, 100] and [155, 155, 155]. It's taking a section right out of the middle of the cube where you say there are more colors. But how many discreet combinations can you make with these RGB numbers?
Now push everything up into the corner so you have RGB values between [200, 200, 200] and [255, 255, 255]. Now how many values do you have? The same, right?
See what's going on there. With a low contrast scene you are not taking a complete cross-section of the RGB cube, you are taking a smaller cube out of the middle of a larger one. In this case with it's own pointy areas around [100, 100, 100] and [155, 155, 155]. This smaller cube 'fits' just fine up in the corner of the big one—they have the same area and shape.
-
You're pretty mixed up here.
Actually it's you who's mixing up things.
And you are using the word luminance incorrectly—it is not the diagonal in an RGB cube ...
The space diagonal in the RGB cube is not the same as luminance, that much is true ... but it basically is some sort of approximation thereof.
... imagine a low-contrast scene with RGB values between [100, 100, 100] and [155, 155, 155].
Interesting thought—you almost pulled me into your delusion. However ... why would a low-contrast scene be limited to to RGB values between (100, 100, 100) and (155, 155, 155)? That does not characterise a low-contrast scene. A limited range of luminance values does. So take all those colours from your triple-100-to-triple-155 sub-cube—and then add all the other RGB values that have the same luminance values as any of the points inside your sub-cube. You'll end up with many more RGB values that definitely do not fit ithe triple-200-to-triple-255 sub-cube.
So please understand: Pushing up the exposure reduces noise, yes, but it also reduces the colour gamut.
The reason why you mostly can get away with ETTR is that in real life, low-contrast scenes (foggy landscape, for instance) usually don't contain particularly saturated colours ... and all in scenes, be their contrast low, medium, or high, the highlights usually are less colourful than the mid-tones (to our eyes, at least). But in those scenes where the brightest tones also are colourful, ETTR needs to be applied with care—especially when you're looking at a luminance histogram (as opposed to a three-channel raw histogram). That's all I'm saying.
-
So please understand: Pushing up the exposure reduces noise, yes, but it also reduces the colour gamut.
Why should that happen?. Changing exposure is just a linear scaling of the captured RGB triplet, RGB={400,200,800} overexposed by 2 stops becomes {1600,800,3200}. If no clipping occurs, how can you say exposing more reduces colour gamut? it will simply have more resolution in defining the colours, and less noise, but not less colour definition.
-
That does not characterise a low-contrast scene. A limited range of luminance values does. So take all those colours from your triple-100-to-triple-155 sub-cube—and then add all the other RGB values that have the same luminance values as any of the points inside your sub-cube. You'll end up with many more RGB values that definitely do not fit ithe triple-200-to-triple-255 sub-cube.
You are trying to have it both ways—you keep talking about luminance when you are making an argument using RGB geometry. There is no luminance axis in this model.
What you seem to be saying is that you want to talk about colors that are not with this 100, 155 cube. I think that's what you are saying when you say "other RGB values that have the same luminance." So take [155, 155, 155] which has a L* value of 65 (in ARGB) and consider other colors which have the same luminance but are more saturated—say a LAB value of (65, 20, 0). This color is no longer in the sub cube, but will be something like [179, 143, 157]. If you include this color in the scene, your sub-cube just got a little bigger and more rectangular, but still you can push the values up until the red channel starts to clip and you'll still have exactly the same number of discreet values. You can't give me any set of RGB numbers that I can't add a constant to and end up with an isomorphic set so long as I don't let the channels clip.
-
Why should that happen?. Changing exposure is just a linear scaling of the captured RGB triplet, RGB={400,200,800} overexposed by 2 stops becomes {1600,800,3200}. If no clipping occurs, how can you say exposing more reduces colour gamut? it will simply have more resolution in defining the colours, and less noise, but not less colour definition.
I think what 01af is saying is that the some colors in volume of colors that are close by in luminance might get out of gamut / clipped if exposure is increased.
Joofa
-
You are trying to have it both ways—you keep talking about luminance when you are making an argument using RGB geometry.
Strange how people falsely believe RGB triples didn't contain any luminance information ... :D
You can't give me any set of RGB numbers that I can't add a constant to and end up with an isomorphic set so long as I don't let the channels clip.
Of course I can't (as long as you include zero to the possible range of constants). But the maximum value of the constant you can add largely depends on the saturation of the most-saturated colour that you want to keep unclipped. That's my point ... it may seem trivial in the context of this disciussion ("do not clip any of the raw channels") but isn't out in the real-life field.
-
So please understand: Pushing up the exposure reduces noise, yes, but it also reduces the colour gamut.
Maybe for example:
D65 white like with sRGB has no real AbsCol representation in a D50 space like ProPhoto RGB.
Channel clipping occurs (and vice versa). At the very top of the gamut even large ProPhoto RGB gets so tiny that a slightly different shade of white can't be held. At least not without reducing exposure / linear downscaling.
No idea though if this would be of any practical (ETTR) relevance here.
Peter
--
-
I think what 01af is saying is that the some colors in volume of colors that are close by in luminance might get out of gamut / clipped if exposure is increased.
So 01af is saying that clipping may occur if we expose too much? such a discovery deserves extra experimentation...
-
Maybe for example:
D65 white like with sRGB has no real AbsCol representation in a D50 space like ProPhoto RGB.
Channel clipping occurs (and vice versa). At the very top of the gamut even large ProPhoto RGB gets so tiny that a slightly different shade of white can't be held. At least not without reducing exposure / linear downscaling.
No idea though if this would be of any practical (ETTR) relevance here.
Peter
--
But, the clipping direction doesn't have to be towards the top near white. It can be sideways.
Joofa
-
So 01af is saying that clipping may occur if we expose too much? such a discovery deserves extra experimentation...
No, if I have understood him correctly, a simple visualization in 2D or 3D might suffice.
Joofa
-
But the maximum value of the constant you can add largely depends on the saturation of the most-saturated colour that you want to keep unclipped.
In other words, expose to the right without clipping color channels. Funny, I thought that's what everyone has been saying the whole time.
-
In other words, expose to the right without clipping color channels. Funny, I thought that's what everyone has been saying the whole time.
No, if I understood him correctly, the clipping he is talking about is in a standardized space, say sRGB, and not camera channel clipping.
Sincerely,
Joofa
-
So 01af is saying that clipping may occur if we expose too much? such a discovery deserves extra experimentation...
Valid point.
The argument that a gamut gets smaller at the top
is annulled by the ETTR constraint to avoid channel clipping.
Peter
--
-
if I understood him correctly, the clipping he is talking about is in a standardized space, say sRGB, and not camera channel clipping.
The argument that a gamut gets smaller at the top
is annulled by the ETTR constraint to avoid channel clipping.
ETTR is about capturing RAW data, just photons being counted by the sensor and producing RGB numbers for which exposure is just a scaling factor. As long as no RAW clipping occurs, exposure in the capture has zero effect on any later colour space transformations.
-
Valid point.
The argument that a gamut gets smaller at the top
is annulled by the ETTR constraint to avoid channel clipping.
Peter
--
I think what he is saying is that if you expose too much then some colors might get clipped in a standardized RGB space even if camera channels are not clipped.
Joofa
-
ETTR is about capturing RAW data, just photons being counted by the sensor and producing RGB numbers for which exposure is just a scaling factor. As long as no RAW clipping occurs, exposure in the capture has zero effect on any later colour space transformations.
So a Raw file would have no color space (http://www.luminous-landscape.com/forum/index.php?topic=22471) ?
Have fun,
and a nice evening.
Peter
--
-
I think what he is saying is that if you expose too much then some colors might get clipped in a standardized RGB space even if camera channels are not clipped.
So a Raw file would have no color space (http://www.luminous-landscape.com/forum/index.php?topic=22471) ?
hehe it could, it could not (who cares?), the fact is that exposure in the capture (which is the only place where discussing about ETTR makes sense), has no consequences in later colour conversions since it can be freely adjusted. Reducing exposure by 2 stops in the RAW data just consists of multiplying all RAW numbers by 0,25.
-
... the fact is that exposure in the capture (which is the only place where discussing about ETTR makes sense), has no consequences in later colour conversions since it can be freely adjusted.
But the photons fist have to pass through the Bayer filters,
which finally define the "Raw gamut" including mentioned tininess at the top.
--
-
Reducing exposure by 2 stops in the RAW data just consists of multiplying all RAW numbers by 0,25.
Yes, true. But, it is a user's prerogative what exposure they want to develop for.
Joofa
-
But the photons fist have to pass through the Bayer filters,
which finally define the "Raw gamut" including mentioned tininess at the top.
--
Guillermo has it right, so long as there is no data loss in capture and the converter treats the data faithfully, nothing is lost in ETTR. ETTR pulled maps to the same output range as a non-ETTR exposure since the pulling is done long before the map to the output color space and any issues associated with colors mapping outside the output gamut. The output routines are dealing with the same data apart from the ETTR data having better S/N.
-
Clipping in a standard space like sRGB or Adobe RGB is a completely separate matter from ETTR. Clipping and gamut issues have to do with the gamut mapping algorithm, not the set of colors the camera can record. The main thing that affects the recorded set of colors is the optical path, namely the spectral transmission of the lens and the spectral sensitivities of the sensor.
You can take pictures of a vivid rose whose tristimulus valued are outside standard color spaces, regardless of what exposure you use.
-
You can take pictures of a vivid rose whose tristimulus valued are outside standard color spaces, regardless of what exposure you use.
I think the issue is that one takes the picture of a rose at some exposure with no clipping when converted to some RGB, and then one increases exposure optically (with no exposure compensation in software) and sees clipping. If that can really happen, and if that is what 01af is saying, then I think it is important that one should be aware of it.
What Gullermo and Emil are saying is fine, but they are operating on a preconceived notion of doing exposure adjustment in software to arrive at a predetermined result. There is no rule in the world that suggests what exposure adjustment to do in software. A user is free to do no exposure adjustment, or worse increase exposure for development, with the possible caveat of clipping occuring.
Sincerely,
Joofa
-
Clipping in a standard space like sRGB or Adobe RGB is a completely separate matter from ETTR. Clipping and gamut issues have to do with the gamut mapping algorithm, not the set of colors the camera can record. The main thing that affects the recorded set of colors is the optical path, namely the spectral transmission of the lens and the spectral sensitivities of the sensor.
You can take pictures of a vivid rose whose tristimulus valued are outside standard color spaces, regardless of what exposure you use.
That is an interesting point. I was under the impression that ProPhotoRGB is able to represent all of the color values captured by the camera. In my own experiments with ETTR, I have encountered clipping with ETTR while rendering into ProPhotoRGB, but this can be removed by decreasing the exposure in ACR. This is not surprising since RGB color space gamuts decrease with luminance. One can also decrease clipping when rendering into sRGB by decreasing the exposure, but it is better to use a wider color space. The critical question with ProPhotoRGB is what exposure value would produce a correct representation of the image.
Regards,
Bill
-
I think the issue is that one takes the picture of a rose at some exposure with no clipping when converted to some RGB, and then one increases exposure optically (with no exposure compensation in software) and sees clipping. If that can really happen, and if that is what 01af is saying, then I think it is important that one should be aware of it.
I confirm you that can really happen, it is called 'RAW clipping'. And ETTR is about preventing it.
What Gullermo and Emil are saying is fine, but they are operating on a preconceived notion of doing exposure adjustment in software to arrive at a predetermined result. There is no rule in the world that suggests what exposure adjustment to do in software. A user is free to do no exposure adjustment, or worse increase exposure for development, with the possible caveat of clipping occuring.
What Emil and me are saying is just that what 01af said is not correct: ETTR does not reduce any colour separation (or whatever he wants to call it).
Your exposure adjustment argument is a fallacy since software exposure adjustment is intrinsic to ETTR, the topic under discussion. Besides that, unless you like greenish images, all RAW files (ETTR'ed and non ETTR'ed) need exposure adjustment performed by the software, it is called white balance.
Regards
-
Bill, when "rendering into" ProPhoto or any other standard colorimetric space, the white balance step is applied and this step can result in clipping (since scale factors are applied to the raw data). For example, a perfectly valid raw red-channel value of a rose at 0.8 (not clipped) may get mapped to 2.0 during white balance, then clipped to the representable output range of [0,1]. Reducing the exposure in software effectively reduces the digital scale factors, and thereby avoids the clipping (*).
So, it is true that the initial rendering of a raw image as seen in a raw converter may appear to have clipped colors when using ETTR, but as long as the original raw channels were not clipped (in the image areas you care about), then you still have all the image data preserved which you can then use to color-map and tone-map as desired (curves, local adjustments, etc.), without loss of detail.
Eric
(*) Of course, reducing the exposure not only removes the clipping, but it also makes the overall image darker, which may or may not be what you really want. That's where tone mapping and really "developing" the picture to taste come into play (separate issue, of course).
-
I confirm you that can really happen, it is called 'RAW clipping'. And ETTR is about preventing it.
I think I mentioned we are talking about RGB space clipping and not raw camera channel clipping.
As Eric Chan mentioned there are ways to avoid RGB clipping, at least in some situations if not all. The sole exercise is knowing the options and possible caveats in increasing optical exposure and possible RGB clipping. Not what you think is the definition of ETTR, or why everybody should adhere to the workflow you want to achieve a preconceived result.
Sincerely,
Joofa
-
What Emil and me are saying ...
Seems we are talking about different subjects.
One question was, if upon increasing exposure, a real-world color could be pushed out of a camera’s gamut. Camera profiles – as can be studied in 3D glory for example here (http://www.drycreekphoto.com/tools/printer_gamuts/) –may look like big matrix spaces, however, they are not endless and get tinier at the top.
My initial assumption was that such out-of-camera-gamut capture would go along / being prevented by Raw channel clipping. Not sure. The alternative would be to receive (unclipped) Raw RGB data which are not unambiguously assigned / interpretable by the corresponding camera profile.
Peter
--
-
Not what you think is the definition of ETTR, or why everybody should adhere to the workflow you want to achieve a preconceived result.
The workflow of ETTR is clear: expose as much as possible in the camera without RAW clipping, and bring exposure back in post processing. There is no link to RGB spaces clipping in the context of ETTR.
Of course you are free to reformulate 'ETTR' in a creative way introducing colour space theory, but that will be a different thing to what this thread is about.
My initial assumption was that such out-of-camera-gamut capture would go along / being prevented by Raw channel clipping. Not sure. The alternative would be to receive (unclipped) Raw RGB data which are not unambiguously assigned / interpretable by the corresponding camera profile.
ETTR doesn't impose any limitation regarding possible gamut clipping after RAW conversion. As long as you don't clip RAW data, everything you can achieve with an ETTR'ed capture is the same that you can achieve with any lower exposure capture, with the difference of having less visible noise.
Regards
-
Of course you are free to reformulate 'ETTR' in a creative way introducing colour space theory, but that will be a different thing to what this thread is about.
Regards
I like it when people want to define what the thread is about, or how it should proceed, or should be interpretted - kind of like my way or the highway. This discussion started from the concerns of 01af regarding the implications of luminance on RGB clipping, so of course color theory is inolved.
Sincerely,
Joofa
-
I think the issue is that one takes the picture of a rose at some exposure with no clipping when converted to some RGB, and then one increases exposure optically (with no exposure compensation in software) and sees clipping.
Of course, but that isn't ETTR - that is just over exposing. It is a well known characteristic and is the basis for muted colors in high-key images (or low-key images for underexposing). Nothing new here, and nothing related to ETTR.
If that can really happen, and if that is what 01af is saying, then I think it is important that one should be aware of it.
If that is what 01af is saying then he is correct, and this has been known well before digital. I can't imagine anyone not being aware of it already. Almost all practical output color spaces have the most saturated colors near middle gray. If you want saturated colors it is best to target those colors for a mid-gray exposure in the output. People did that with Kodachrome for ages and ages. Very old news.
This isn't relevant at all to ETTR assuming your ETTR exposure doesn't clip any RAW color channels (outside of specular highlights). What it is relevant to is your output color space which occurs after exposure adjustments have been made to the RAW data. When exposure compensation is applied in the RAW converter the output tones will be back in the widest part of the gamut. If there was no channel clipping these exposure compensated channel levels will be identical to those of a "normal" exposure and the output gamut at that tonal level will be the same. There will just be lower photon shot noise in the ETTR exposure, the whole point of ETTR.
What Gullermo and Emil are saying is fine, but they are operating on a preconceived notion of doing exposure adjustment in software to arrive at a predetermined result.
But that is the notion of ETTR - expose above your intended output exposure if there is headroom to spare. If you aren't doing exposure adjustment in software then you aren't doing ETTR, you are just following the camera metering.
There is no rule in the world that suggests what exposure adjustment to do in software. A user is free to do no exposure adjustment, or worse increase exposure for development, with the possible caveat of clipping occuring.
Of course, again high-key and low-key photography. It isn't limited to software at all either. This decision is made in camera with transparencies, at printing time with negatives, in PP or in camera with JPEGs, and ideally in the RAW converter with RAW images.
I just don't see how any of 01af's discussion or your points here are relevant to ETTR. We are now talking about color representation in the processed photo after artistic decisions. That has little if anything to do with ETTR. ETTR is simply getting the lowest noise photon counts without introducing non-linearity (clipping) for any relevant scene detail. It is a fairly mechanical process. The question of output exposure comes afterwords and is independent of whether the exposure was "normal" or ETTR.
af01 hasn't been very clear about what issue he is addressing. If it is about output color spaces and the limited gamut width in the highlights and shadows, well then "duh", I don't think anyone is going to consider that news. If he is claiming that an ETTR exposure without clipped RAW channels has a restricted gamut compared to a lower exposure after both have been properly exposure compensated in the RAW converter then he is flat out wrong - plain and simple.
Ken
-
I just don't see how any of 01af's discussion or your points here are relevant to ETTR.
I have tried not to define what exactly is ETTR or what is relevant to ETTR. I have just tried to present what I thought 01af meant as it seems almost everybody could not figure out what he was trying to say - most here were mixing raw clipping with RGB clipping, when I thought that 01af meant RGB clipping. May be he means something totally different.
Sincerely,
Joofa
-
One question was, if upon increasing exposure, a real-world color could be pushed out of a camera’s gamut. Camera profiles – as can be studied in 3D glory for example here (http://www.drycreekphoto.com/tools/printer_gamuts/) –may look like big matrix spaces, however, they are not endless and get tinier at the top.
My initial assumption was that such out-of-camera-gamut capture would go along / being prevented by Raw channel clipping. Not sure. The alternative would be to receive (unclipped) Raw RGB data which are not unambiguously assigned / interpretable by the corresponding camera profile
--
It may seem pedantic, but digital cameras and other input devices do not have a gamut, as strictly defined (see the Munsell FAQ (http://www.cis.rit.edu/mcsl/faq3#255)). Therefore, it would not be possible to push a color beyond the "gamut" of the camera. However, digital sensors do clip. I am not sure that this clarifies the topic under discussion, but it is an interesting fine point.
Regards,
Bill
-
I like it when people want to define what the thread is about, or how it should proceed, or should be interpretted - kind of like my way or the highway. This discussion started from the concerns of 01af regarding the implications of luminance on RGB clipping, so of course color theory is inolved.
Sincerely,
Joofa
This thread was started by ErikKaffehr, not by O1af, who didn't pipe in until reply # 142. Go back to Erik's original post and you will see that the thread did indeed start with Erik's comments about ETTR, and NOT about O1af's concerns about luminance. Nevertheless, O1af's ambiguous suggestions seem to me to have been answered pretty effectively by several knowledgable responders/
-
I have tried not to define what exactly is ETTR or what is relevant to ETTR. I have just tried to present what I thought 01af meant
Ah, got it. Thanks! Maybe he'll swing by again and let us know.
Cheers,
Ken
-
If that is what 01af is saying then he is correct, and this has been known well before digital. I can't imagine anyone not being aware of it already. Almost all practical output color spaces have the most saturated colors near middle gray. If you want saturated colors it is best to target those colors for a mid-gray exposure in the output. People did that with Kodachrome for ages and ages. Very old news.
It depends on how you look at it. If you view the RGB cube in a perceptual space, for example CIELAB, the maximum available saturation does not necessarily correspond to the mid-gray. This example shows that in AdobeRGB, the maximum chroma is nearest to the lightness of white for yellow, green, and cyan.
(https://sites.google.com/site/cliffpicsmisc/home/coloe/AdobeRGBinLab.png)
(image created with RGB Cube (http://www.couleur.org/index.php?page=rgbcube))
-
It depends on how you look at it. If you view the RGB cube in a perceptual space, for example CIELAB, the maximum available saturation does not necessarily correspond to the mid-gray. This example shows that in AdobeRGB, the maximum chroma is nearest to the lightness of white for yellow, green, and cyan.
That is a good point, but it is difficult to read the luminance at maximum chroma from your 3-D graph. A better view can be obtained in ColorThink Pro using the slicer. The maximum chroma for cyan occurs at a L* of about 87 as shown below. Nonetheless, a RGB space such as AdobeRGB does have decreased chroma as L* approaches 100 as shown in the second image, even though maximal chroma does not occur at L* of 50. As previously pointed out, one can place the luminance as desired when rendering a raw ETTR into aRGB and it is not necessary to expose for mid-gray. Chroma clipping can be reduced by rendering into ProPhotoRGB.
Regards,
Bill
-
That is a good point, but it is difficult to read the luminance at maximum chroma from your 3-D graph. A better view can be obtained in ColorThink Pro using the slicer. The maximum chroma for cyan occurs at a L* of about 87 as shown below. Nonetheless, a RGB space such as AdobeRGB does have decreased chroma as L* approaches 100 as shown in the second image, even though maximal chroma does not occur at L* of 50. As previously pointed out, one can place the luminance as desired when rendering a raw ETTR into aRGB and it is not necessary to expose for mid-gray. Chroma clipping can be reduced by rendering into ProPhotoRGB.
AdobeRGB maximum chroma yellow (255,255,0) is at L* = 97. Max blue chroma (0,0,255) is at L* = 33. I think it is safe to say that one can't generalize about which luminance or lightness will yield the strongest colors. It depends on both the particular color, and the color space.
I agree with you and the others who say that, as long as there is no clipping, ETTR can be used without losing any colors in the capture. Has anyone produced a demonstration that proves otherwise?
On the output side, there is a related problem reproducing scenes with highly-chromatic white points. Here is an interesting paper by Heckaman & Fairchild, "Expanding display color gamut beyond the spectrum locus." (http://www.cis.rit.edu/fairchild/PDFs/PAP22.pdf) View the example images full screen in a dark room - very effective! They call it “pushing down the white point of the display." Around here it might be called Display To The Middle. :D
-
It depends on how you look at it. If you view the RGB cube in a perceptual space, for example CIELAB, the maximum available saturation does not necessarily correspond to the mid-gray. This example shows that in AdobeRGB, the maximum chroma is nearest to the lightness of white for yellow, green, and cyan.
Yes, thank you for correcting my oversimplification. It really depends on the chromaticities of the primaries of the color space.
Ken
-
Second, ETTR will optimize separation of tones but sacrifice separation of colours. So if the subject's dynamic range is small then don't push it up all the way to the right. Instead, leave it centered ... or push it up half-way between center and right.
...
For the optimal exposure, you'd need to balance dynamic range versus colour range.
So after a couple of pages of discussion, it seems to me that 01AF thinks that ETTR means undesirabe clipping (either in camera or in raw development), while most others think that is generally wrong, and everyone agress that clipping is bad for colors?
While having example images showing what one tries to argue is always a good thing, I think that what is really needed is a common understanding of what ETTR really means. If everyone use their own definition of ETTR, then discussing it merits (or lack thereof) is pointless.
-h
-
And if someone, who isn't as knowledgeable and is trying to learn and hoping for a consensus of opinion, is lurking then it is disappointing, to say the least. What probably makes it worse is that there are one or two stirring the pot and obscuring any real information. Then again I and others have been told that we don't need to read if we don't have to? :-\
-
And if someone, who isn't as knowledgeable and is trying to learn and hoping for a consensus of opinion, is lurking then it is disappointing, to say the least. What probably makes it worse is that there are one or two stirring the pot and obscuring any real information. Then again I and others have been told that we don't need to read if we don't have to? :-\
What are you saying?
Total consensus of opinion is very rare. This is the case for academia, politics and internet forums. Part of the skill-set needed to learn from these sites is being able to distinguish relevant, knowledgeable posts from posts that are less so, and to repeat important tests for yourself when needed.
01af have been asked to provide images /test-procedures that supports his claim. When he/she does so, it will be a lot easier for us to understand what he/she really means, and how relevant it is to our own line of photography.
-h
-
It may seem pedantic, but digital cameras and other input devices do not have a gamut, as strictly defined (see the Munsell FAQ (http://www.cis.rit.edu/mcsl/faq3#255)). Therefore, it would not be possible to push a color beyond the "gamut" of the camera. However, digital sensors do clip. I am not sure that this clarifies the topic under discussion, but it is an interesting fine point.
Yes, that’s an quite academic definition of "color gamut"
which also seems to consider that a camera is supposed to react on any light source such as e.g. a spectrally pure laser beam, even though such stimulus may lie outside of what we draw as a camera color space.
Anyway, the final conclusion that it doesn’t matter here for ETTR sounds logical,
and Guillermo is of course right when saying that any +Eposure can be undone by linear down-scaling of the (unclipped) Raw RGB data.
Could still be interesting to hear the "defense" of Andrey Tverdokhleb and Iliah Borg
who brought up this thesis about "ETTR is very harmful for colors - midpoint is the most colorful place in A900 gamut" as quoted here (http://www.luminous-landscape.com/forum/index.php?PHPSESSID=a09a1fe90f43a3f3dbeabf33e346cecf&topic=56469.msg459780#msg459780).
Best regards, Peter
--
-
Could still be interesting to hear the "defense" of Andrey Tverdokhleb and Iliah Borg
who brought up this thesis about "ETTR is very harmful for colors - midpoint is the most colorful place in A900 gamut" as quoted here (http://www.luminous-landscape.com/forum/index.php?PHPSESSID=a09a1fe90f43a3f3dbeabf33e346cecf&topic=56469.msg459780#msg459780).
Best regards, Peter
--
The important comment is this one:
Veiling glare from lens and sensor are the culprits here
Nothing to do with ETTR at least from the theoretical point of view. If RAW channels aren´t clipped, there will be no issues with colors unless some external factor (like veiling glare) is involved.
-
Yes, that’s an quite academic definition of "color gamut"
which also seems to consider that a camera is supposed to react on any light source such as e.g. a spectrally pure laser beam, even though such stimulus may lie outside of what we draw as a camera color space.
I could imagine that a camera with "weak" color filters on the Bayer array would have trouble distinguishing a spectrally pure laser beam from a less pure color. (Instead of calling it a color space, I have read the camera spaces being described as a "spectral spaces" since they have responses different from the eye.)
Anyway, the final conclusion that it doesn’t matter here for ETTR sounds logical,
and Guillermo is of course right when saying that any +Eposure can be undone by linear down-scaling of the (unclipped) Raw RGB data.
+1
Could still be interesting to hear the "defense" of Andrey Tverdokhleb and Iliah Borg
who brought up this thesis about "ETTR is very harmful for colors - midpoint is the most colorful place in A900 gamut" as quoted here (http://www.luminous-landscape.com/forum/index.php?PHPSESSID=a09a1fe90f43a3f3dbeabf33e346cecf&topic=56469.msg459780#msg459780).
In that quote Andrey says:
Veiling glare from lens and sensor are the culprits here.
Interesting that they don't blame the shape of the RGB color space. I just don't see how exposure can affect the proportion of veiling glare in the image, other than by changing the aperture, which of course changes other things too. If you increase the exposure time without clipping (- what's that called again?) how could that change the percent of flare/glare in the image? Hopefully Andrey or Iliah could elaborate.
-
Could still be interesting to hear the "defense" of Andrey Tverdokhleb and Iliah Borg
who brought up this thesis about "ETTR is very harmful for colors - midpoint is the most colorful place in A900 gamut" as quoted here (http://www.luminous-landscape.com/forum/index.php?PHPSESSID=a09a1fe90f43a3f3dbeabf33e346cecf&topic=56469.msg459780#msg459780).
ETTR is about getting the optimal exposure from the sensors, on cameras that were calibrated to actually ETTL (from the point of view of the optimal sensor exposure). Cameras were exposing to the left essentially for two reasons
- sensors and their back office electronics implementation had a somewhat limited DR compared to what the human eye expected to see.
- engineers decided that it was better to protect from over-exposure (where data is simply lost) than fully exploit low light situations.
Sensors and their backend pipeline have improved, drastically in some cases, and that has extended the margins of DR on both sides to the point that, in some recent cameras, you just don't care.
To summarize
- there are situations where ETTR is very useful (typically, Canon 5D MK II)
- there are situations where ETTR is either almost useless or harmful: the cameras that don't ETTL from the sensor point of view in the first place.
Don't forget that sensors that are very different in terms of raw capabilities are normalized for the average photographer's comfort. ISO 100 is an important reference point for photographers and should yield, give or take a bit, a similar result in all cameras. But one you've got enough DR, for example because you handle read noise better than your competitor, you can adjust gain to put it where you want it in your optimal sensor linear range.
ETTR will become more andmore useless as sensors improve in all brands. No need try to find esoteric arguments against it.
-
ETTR will become more andmore useless as sensors improve in all brands. No need try to find esoteric arguments against it.
The same could be said about resolution; yet as we get ever more resolution, many still crave for more.
As the public taste for HDR (and available, good quality tonemapping appears), the possibility of doing "HDR" for demanding scenes easily even when there is movement and the tripod is at home could be important.
No matter how good image capture is, there is always going to be someone wanting even more accurate capturing, and ETTR seems to be something to be aware of if you want to optimize "SNR".
-h
-
The same could be said about resolution; yet as we get ever more resolution, many still crave for more.
As the public taste for HDR (and available, good quality tonemapping appears), the possibility of doing "HDR" for demanding scenes easily even when there is movement and the tripod is at home could be important.
No matter how good image capture is, there is always going to be someone wanting even more accurate capturing, and ETTR seems to be something to be aware of if you want to optimize "SNR".
I don't agree here. There will be a day when a user will say 'STOP'. You don't bracket a LDR scene, do you? even if you can afford to. When a time comes in which HDR scenes can be captured in a single shot, users won't bother to bracket (bye bye to misalignment issues or ghosting artifacts, less resources needed, handheld HDR).
The same applies to ETTR (for the same reason: sensor noise lowering). If you can afford to underexpose and still have a high quality image, you won't bother to ETTR. In fact you'll probably try not to ETTR in order to make sure highlights are preserved without caring too much about exposure. This will allow to shoot faster and concentrate on other aspects like composition.
This image was underexposed by 6 stops on a Pentax K5 (6 upper stops in the histogram with no information):
(http://www.guillermoluijk.com/article/perfect/histraw.gif)
(left camera JPEG, right processed RAW)
(http://www.guillermoluijk.com/article/perfect/antesdespues1.jpg)
It's a extreme non-ETTR, but still the resulting image was quite OK. If underexposure had been just by 3 stops (still a huge gap from perfect ETTR), the IQ would have been the same as with ETTR in practice.
Regarding resolution, I am happy Olympus stayed at 12Mpx (unfortunately they'll probably go into 16Mpx for marketing reasons). I not only don't need more, in this case I don't want more because more Mpx mean a lot of disk space and processing power, with nearly no quality improvement for my pictures. Others will stop at 24Mpx, but sooner or later the pixelcount race will come to an end for every user. Digital photography is a young technology, the race is still in progress, that's all.
Regards
-
The same applies to ETTR (for the same reason: sensor noise lowering). If you can afford to underexpose and still have a high quality image, you won't bother to ETTR. In fact you'll probably try not to ETTR in order to make sure highlights are preserved without caring too much about exposure. This will allow to shoot faster and concentrate on other aspects like composition.
As I read Emil's guidance, I thought he said it was always of advantage to ETTR, as it would maximize the exposure. The question was whether there was any advantage to use ISO to achieve this with some of the newer CMOS sensors (and the CCD sensors).
I agree that if one can "still have a high quality image", you may want to concentrate on other aspects. However, that does not diminish the ability of ETTR, properly applied, to improve on image quality.
John
-
I don't agree here. There will be a day when a user will say 'STOP'. You don't bracket a LDR scene, do you? even if you can afford to. When a time comes in which HDR scenes can be captured in a single shot, users won't bother to bracket (bye bye to misalignment issues or ghosting artifacts, less resources needed, handheld HDR).
No disagreement here, we both seem to argue for "single-shot" HDR: camera and exposure techniques that, when combined, record a large DR in a single shot.
But how much sensor DR is enough? How small does the noise contribution have to be before you and everyone else think that "nah, good enough now"? And as a consequence, when are the sensors good enough that you can afford to be sloppy with exposure (or choose to use insane margins against clipping)? My guess is "never". Even a very low DR scene could benefit from having a low noise level?
I see ETTR more as a question of "how and how much should I ETTR this scene/sensor", not "if the upper 5% quantile of the histogram cross the 95% clipping limit of the sensor, then and only then do you have ETTR". For SLR auto-exposure, targeting a 18% grey, or N stops below clipping point or whatever, may be a sane general mechanism. For digital compacts (where exposure can be based on image sensor readouts), perhaps something different. For manual exposure where the user has artistic intensions with the scene, some other choices may fit. In the end, what matters is the exposure time, aperture, in-camera ISO, and how they affect the raw file and the posibilities when developing that raw file. What I gather from these discussions is that there is (often, but not always) a free but small lunch to be had, IQ-wise by increasing either aperture or exposure time if you can avoid clipping with some certainty. Sometimes this is a trained skill where you know that +1 stop of EC is ok, other times you may consult the in-camera histogram (after reverting as much as possible of the in-camera JPEG image processing), other times it may result from simply doing brute-force bracketing.
-h
-
that does not diminish the ability of ETTR, properly applied, to improve on image quality.
If the improvement is not visible, the improvement doesn't exist in practice.
If a computer can perform your daily task 10 times faster than another computer, you could think it's a good idea to pick the fast one. But if the slow computer performs the task in a milisecond, and the fast one in 1/10 of a milisecond, spending a single extra euro on the fast computer is a waste of money because you'll never enjoy the advantage in practice.
Going to photography, if your sensor with ETTR has a SNR=60dB, and without ETTR a SNR=40dB, you are wasting your time putting any effort on ETTR because to your eyes both exposures will be as good.
This is what I mean by ETTR becoming less and less useful (so as bracketing for HDR). ETTR will always reduce noise, but at some point that reduction will not be worth the effort to achieve ETTR. When? that will be progressively decided by each user, it's a matter of balance: effort/disadvantages of ETTR vs less visible noise.
when are the sensors good enough that you can afford to be sloppy with exposure (or choose to use insane margins against clipping)? My guess is "never"
Hey, I wonder if you had a look at the 6-stops underexposed example.
Regards
-
Yes, that’s an quite academic definition of "color gamut"
which also seems to consider that a camera is supposed to react on any light source such as e.g. a spectrally pure laser beam, even though such stimulus may lie outside of what we draw as a camera color space.
The definition of a camera gamut may seem academic, but examination of the spectral response of existing cameras shows that they do respond to wavelengths of 4,000 to 7,000 A, pretty much the range of human vision. The graph shown below is from Christian Buil's web site (http://astrosurf.com/buil/d70v10d/eval.htm). This is consistent with the RIT that a digital camera will give a response to what ever is put in front of it. Perhaps you could say that the gamut of these cameras is 4,000 to 7,000 A.
You referenced an earlier thread in which I was involved, Does a Raw File Have a Color Space? (http://www.luminous-landscape.com/forum/index.php?topic=22471) That depends on the definition of what constitutes a color space. The camera does have RGB sensors and we use matrix math to convert from the camera "space" to CIE XYZ or some other well defined space. CIE XYZ gives exact results, but the camera "space" does not because of metameric error. The matrix coefficients used to convert to XYZ are merely a best fit approximation. In this regard, you could say that the camera space is not a fully defined color space. These considerations are well covered in a paper by Doug Kerr (http://dougkerr.net/pumpkin/articles/Sensor_Colorimetry.pdf) where he discusses the Luther-Ives conditions, metameric error and other technicalities of digital sensors.
Regards,
Bill
-
That depends on the definition of what constitutes a color space.
In colorimetry there is a well-defined notion of a linear color space:
(1) Specification of primaries.
(2) Specification of white point.
Let's not worry about other stuff such as gamma, LUTs, etc., as they are used for further encoding a color value, and are not inherently needed for the definition of a linear color space.
If you think that the above two are satisfied for a camera then one may be able to say that there is a camera color space.
Sincerely,
Joofa
-
In colorimetry there is a well-defined notion of a linear color space:
(1) Specification of primaries.
(2) Specification of white point.
Let's not worry about other stuff such as gamma, LUTs, etc., as they are used for further encoding a color value, and are not inherently needed for the definition of a linear color space.
If you think that the above two are satisfied for a camera then one may be able to say that there is a camera color space.
The issue is that, unless the Luther-Ives conditions are met (fancy way of saying that the spectral responses are linearly related to the CIE standard observer responses), then the camera primaries and XYZ define different three-dimensional linear subspaces of the much higher dimensional linear space of all possible spectral responses. So yes a digital camera has intrinsically a linear space of spectral responses, but it is not related a priori to the spectral responses that define any of the color spaces used in colorimetry. So if the term 'color space' is reserved to the CIE's definition of color, tristimulus, etc, then no, a camera typically does not have a color space. If the term is meant more loosely, then one might say that it does have one.
-
The issue is that, unless the Luther-Ives conditions are met (fancy way of saying that the spectral responses are linearly related to the CIE standard observer responses), then the camera primaries and XYZ define different three-dimensional linear subspaces of the much higher dimensional linear space of all possible spectral responses. So yes a digital camera has intrinsically a linear space of spectral responses, but it is not related a priori to the spectral responses that define any of the color spaces used in colorimetry. So if the term 'color space' is reserved to the CIE's definition of color, tristimulus, etc, then no, a camera typically does not have a color space. If the term is meant more loosely, then one might say that it does have one.
Correct. I agree with you.
Sincerely,
Joofa
-
A camera can capture and encode colors as unique values compared to others, that are imaginary to humans. They don't exist (are they colors?). There are colors we can see, but the camera can't capture, the colors are imaginary to it. So what is to be done with these captured values that humans can't see? They may get mapped to something. Possibly something that another rather different SPD is already mapped to. Two reds that appear the same to us, but have different SPDs, the camera captures as different colors. So it encodes them with two different RGB values. A camera can capture all sorts of different primaries. Two different primaries may be captured as the same values by a camera, and the same primary may be captured as two different values by a camera (if the SPD of the primaries are different). If we had spectral sensitivities for the camera, that would make the job of mapping to XYZ better and easier, but we'd still have decisions on what to do with the colors the camera encodes, that are imaginary to us.
-
A camera can capture and encode colors as unique values compared to others, that are imaginary to humans. They don't exist (are they colors?). There are colors we can see, but the camera can't capture, the colors are imaginary to it. So what is to be done with these captured values that humans can't see? They may get mapped to something. Possibly something that another rather different SPD is already mapped to. Two reds that appear the same to us, but have different SPDs, the camera captures as different colors. So it encodes them with two different RGB values. A camera can capture all sorts of different primaries. Two different primaries may be captured as the same values by a camera, and the same primary may be captured as two different values by a camera (if the SPD of the primaries are different). If we had spectral sensitivities for the camera, that would make the job of mapping to XYZ better and easier, but we'd still have decisions on what to do with the colors the camera encodes, that are imaginary to us.
Good points, but many digital cameras have little response to wavelengths outside of the range of human vision, roughly 400-700 nm. The spectral responses of the cameras studied by Christian Buil (referenced in my previous post in this thread) are roughly 400-700 nm. Most digital sensors have an extended infrared sensitivity, and infrared cutoff filters are usually employed to limit the response to visible wavelengths. Lack of such filters causes problems in color rendering as evidenced by the Leica M8 (which lacked such a filter). Leica had to supply a filter that fits on in front of the lens. I haven't read about the effect of extended ultraviolet sensitivity. Perhaps someone can comment.
Regards,
Bil
-
Good points, but many digital cameras have little response to wavelengths outside of the range of human vision, roughly 400-700 nm. The spectral responses of the cameras studied by Christian Buil (referenced in my previous post in this thread) are roughly 400-700 nm. Most digital sensors have an extended infrared sensitivity, and infrared cutoff filters are usually employed to limit the response to visible wavelengths. Lack of such filters causes problems in color rendering as evidenced by the Leica M8 (which lacked such a filter). Leica had to supply a filter that fits on in front of the lens. I haven't read about the effect of extended ultraviolet sensitivity. Perhaps someone can comment.
If I point an IR remote into any camera, it will usually record light, while pointing it into my eyes I cannot see anything.
So cameras have 3 sets of spectrall bandpass-filters that are similar but not identical to the standardized human response. And the response of my vision might be slightly different from yours. Did you know that something like 10% of all women have 4 sets of bandpass filters in their eyes (although it is unknown if they are able to make use of that information, I dont doubt it when discussing clothes or interior design with them).
Besides being academically interesting, how does this affect the relatively simple question of "how should I expose my digital camera sensor to maximize image quality"?
-h
-
Besides being academically interesting, how does this affect the relatively simple question of "how should I expose my digital camera sensor to maximize image quality"?
Simply: It doesn't.
I'll say it again: ETTR has nothing to do with color. It has everything to do with maximizing signal-to-noise, as permitted by shooting conditions. This is independent of the spectral sensitivities of the cameras, potential UV/IR response, whether or not the filters are "colorimetric", etc. Example: The Leica M8, Canon S90, Nikon D3, and Phase One P65+ have very different spectral sensitivities. However, they have something in common: the more light you capture with them, the higher the signal-to-noise, and the cleaner the results will be. So, whichever of these cameras you may have, the advice remains the same: when the situation allows, capture as much light as possible while avoiding clipping in the areas of the image that you care about.
Mapping the raw color values into standard working spaces (or display & printer spaces) is a matter of gamut mapping as implemented by the raw conversion software. As long as you didn't clip something in the raw data that you care about, then the information is all there and you can make use of it.
-
Mapping the raw color values into standard working spaces (or display & printer spaces) is a matter of gamut mapping as implemented by the raw conversion software. As long as you didn't clip something in the raw data that you care about, then the information is all there and you can make use of it.
At least from an information-theoretical viewpoint.
If you use a raw developer that does not allow you to accurately change exposure (multiply raw input data), but mess with the colors at the same time, then your options are to:
1. Change your raw developer
2. Live with whatever color change happens
3. Expose in-camera closer to how you would like the end-exposure on paper/screen (Not use ETTR)
-h
-
At least from an information-theoretical viewpoint.
If you use a raw developer that does not allow you to accurately change exposure (multiply raw input data), but mess with the colors at the same time, then your options are to:
1. Change your raw developer
....
Another option is to learn how to use the raw converter that you do have properly. For example, see the post by Sandymc (http://www.luminous-landscape.com/forum/index.php?topic=56863.msg462715#msg462715) summing up his investigations on the problems with hue twist in ACR with Eric Chan. The point about the black slider set to zero is a bit confusing, since Eric had stated in another post (http://www.luminous-landscape.com/forum/index.php?topic=56863.msg461459#msg461459) that the blacks were set prior to the application of the 3D lookup table. What is the official recommendation?
Regards,
Bill
-
I cannot speak for other raw converters. But if you're using ACR or Lightroom, my personal (not official) recommendation is simply to use Exposure to compensate for whatever additional in-camera exposure you may have used. For example, if you did ETTR by adding +1 stop of exposure at time of capture, try setting Exposure -1 in ACR/LR. This will not result in hue shifts compared to if you hadn't used ETTR.
-
But if you're using ACR or Lightroom, my personal (not official) recommendation is simply to use Exposure to compensate for whatever additional in-camera exposure you may have used. For example, if you did ETTR by adding +1 stop of exposure at time of capture, try setting Exposure -1 in ACR/LR. This will not result in hue shifts compared to if you hadn't used ETTR.
Wouldn't this require a profile with lightness-dependent Hue/Sat.-corrections ?
I'm referring to the first table for accuracy, such as in particular from the Chart Wizard,
not any 3D Look table which may come later on, after the Exposure slider in the processing pipe.
Peter
--
-
One of the "gripes" and "desires" is that the histogram isn't based on raw data (to allow for clip detection) and that it should be...
From the new story by Nick Rains comes the following from his "interview" with Leica:
There is a rumour on the Internet Forums that the histogram on the S2 is raw based – is this true?
No, it is based on the jpeg preview. A histogram from raw data is not possible as the image cannot be said to exist yet. A white balance needs to be chosen and the red blue and green channels need to be combined to give a meaningful histogram. So we always give you more than you think. If your histogram is good, then you will actually have more data in the raw file than you expect.
-
That particular answer, which I also just read, strikes me as totally confusing and utterly uninformed. In fact, this is a ridiculous/hilarious statement.
The data is there: that is the data they generate the jpeg from, and then subsequently generate the histogram of the jpeg from.
So you have
-> data (let's be generous and say 16-bit values for each x y point in the array)
-> relatively complex transformation of the above data in a x-y array of 8 bit values
-> generation of an histogram of those 8 bit values
and the claim is
-> same data
-> generation of an histogram of those 16 bit values
is impossible.
Jesus! How can one be so dense (sorry)! If they want, they can generate an histogram of how many pictures users take every hour or anything else they measure.
Now, of course, if a Leica executive said it, you can be sure it will become gospel for thousands of photographers. But that is utterly absurd: gazillions of histograms are generated on a continous base by zillions of sensor users who just want ot generate histograms.
Even if you don't care a bit about the technicalities, one has got to admire the logic of the process.
"we don't generate an histogram of the raw data because the picture doesn't exist, yet susprisingly the picture exists enough to derive a jpeg from that very same raw data and then an histgram of that jpeg...."
Priceless.
-
Nick Rains surely heard of histograms for the first time applied to digital cameras, and he probably isn't aware that those population pyramids he studied at school were histograms as well:
(http://tungwaiyip.info/2007/img/hk_population_pyramid_2006.png)
A genuine Canon 5D RAW histogram, showing non-zero black point and non max saturation point (3692). If no gamma is applied, the linear histogram is of little use to the photographer since it is concentrated on the left side due to sensor linearity:
(http://www.guillermoluijk.com/tutorial/satlevel/hist5d.gif)
A simple gamma curve, or even better a log representation in the X-axis, make the histogram very meaningful to the photographer.
Here RAW histograms in EV divisions for different exposures 1 stop apart (note the histogram doesn't change in shape thanks to the log scale):
(http://www.guillermoluijk.com/article/spot/nube.gif)
A quick glance provides information about any RAW clipping, highlight exposure headroom in EV (perfect for ETTR!) and scene's DR.
Regards
-
A quick glance provides information about any RAW clipping, highlight exposure headroom in EV (perfect for ETTR!) and scene's DR.
Hi Guillermo,
I agree with an EV based representation. In addition, IMHO, a histogram for the purpose of detecting clipping issues would become even more useful if the bin counts (vertical axis) are also represented on a logarithmic scale. For determining optimal exposure I'm less interested in the bins with a high count, and more interested in the ones with low counts, e.g. for detecting the onset of clipping by specular highlights.
Cheers,
Bart
-
Hi Guillermo,
I agree with an EV based representation. In addition, IMHO, a histogram for the purpose of detecting clipping issues would become even more useful if the bin counts (vertical axis) are also represented on a logarithmic scale. For determining optimal exposure I'm less interested in the bins with a high count, and more interested in the ones with low counts, e.g. for detecting the onset of clipping by specular highlights.
Agreed; it would also be trivial to give some indicators, say 0.001 fraction clipped, 0.01 fraction clipped, etc.
-
But if you're using ACR or Lightroom, my personal (not official) recommendation is simply to use Exposure to compensate for whatever additional in-camera exposure you may have used. For example, if you did ETTR by adding +1 stop of exposure at time of capture, try setting Exposure -1 in ACR/LR. This will not result in hue shifts compared to if you hadn't used ETTR.
Wouldn't this require a profile with lightness-dependent Hue/Sat.-corrections ?
I'm referring to the first table for accuracy, such as in particular from the Chart Wizard,
not any 3D Look table which may come later on, after the Exposure slider in the processing pipe.
Inconvenient question,
or just irrelevant, or just no time for being around ???
Anyway. Cheers!
& Best regards, Peter
--
-
"we don't generate an histogram of the raw data because the picture doesn't exist, yet susprisingly the picture exists enough to derive a jpeg from that very same raw data and then an histogram of that jpeg...."
;D :D ;D
Yes, that's quite puzzling indeed. Why?
-
I don't agree here. There will be a day when a user will say 'STOP'. You don't bracket a LDR scene, do you? even if you can afford to. When a time comes in which HDR scenes can be captured in a single shot, users won't bother to bracket (bye bye to misalignment issues or ghosting artifacts, less resources needed, handheld HDR).
The same applies to ETTR (for the same reason: sensor noise lowering). If you can afford to underexpose and still have a high quality image, you won't bother to ETTR. In fact you'll probably try not to ETTR in order to make sure highlights are preserved without caring too much about exposure. This will allow to shoot faster and concentrate on other aspects like composition.
This image was underexposed by 6 stops on a Pentax K5 (6 upper stops in the histogram with no information):
It's a extreme non-ETTR, but still the resulting image was quite OK. If underexposure had been just by 3 stops (still a huge gap from perfect ETTR), the IQ would have been the same as with ETTR in practice.
The quality of the 6 stops underexposed image with the K5 is astounding, but I don't think that is a good excuse to become sloppy in exposure. The image under discussion was relatively low dynamic range and viewed at low magnification. One must remember that for each halving of exposure, one loses 1 stop of DR and the SNR increases by a factor of 1.4. These facts are shown in measurements by DXO for the Nikon D7000, which uses the same sensor. The results are for ISO and not exposure, but these new cameras are effectively ISO-less and the results of increasing the ISO are similar to those obtained by underexposure.
For optimum results with a high dynamic range image scene, one should fully utilize ETTR. For less demanding shots, one can leave a bit of highlight headroom for safety. IMHO, these cameras with better sensor performance do not negate the benefits of ETTR, but change our approach to utilizing it.
Regards,
Bill
-
For less demanding shots, one can leave a bit of highlight headroom for safety. IMHO, these cameras with better sensor performance do not negate the benefits of ETTR, but change our approach to utilizing it.
We are saying the same thing Bill, the better sensors become, the less need for ETTR. Or what is the same, the less need to bother about achieving perfect ETTR.
If my camera has an effective DR of 11 stops, and the scene's DR is just 7 stops, I could be even more interested in doing ETTR-2EV than perfect ETTR. This will give me two extra stops of shutter speed (always a good idea for sharpness), and extra safety headroom for highlight clipping at no practical IQ cost in the final image:
Camera's DR: ***********
ETTR: ----OOOOOOO
ETTR-2: --OOOOOOO--
-
If my camera has an effective DR of 11 stops, and the scene's DR is just 7 stops...
Most people, even most photographers might not care less what Dynamic Range is.
For those that do care, I suspect that they would rather have 6 stops than 4 stops of SNR in the darkest tones, if cost only a slight inconvenience.
I tend to see the whole "ETTR" thing to be a discussion on the "right exposure", not "exposing as much as possible to the right". Right now, photographers have poor in-camera feedback to tell them exactly how an image was/will be exposed, and therefore, they will tend to introduce some margins that may or may not be needed or wanted in a particular image. If and when those feedback mechanisms are improved, the photographer will have more control over the exposure. That will result in a better ability to utilize each sensor generation closer to its fullest, no matter how much progress is made in the core sensor abilities.
-h