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Author Topic: Better than ETTR ?  (Read 34247 times)

Bart_van_der_Wolf

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Re: Better than ETTR ?
« Reply #40 on: August 08, 2011, 04:33:13 am »

Can you show us an example where a noise remover did a better job thanks to having more levels?.

I don't have a camera with variable bit-depth, but I can imagine that as the precision of the noise quantization improves, it also becomes a little easier to remove the noise. The difference will be marginal though, so it might benefit e.g. astrophotography (by averaging multiple calibrated exposures) more than, say, sports photography.

Quote
In the article: DO RAW BITS MATTER? I developed some RAW files with a decreasing number of bits (i.e. I rounded RAW numbers before demosaicing to emulate ADC with less bits).

Yes, that's an interesting article.

Quote
For the Canon 40D, 12bits showed to be enough. The extra 2 bits didn't improve useful information recorded:

Actually I think the difference is noticeably more smooth without the coarser quantization posterization, but perhaps I am hyper-sensitive to it. It was the same when I switched from the EOS 1Ds2 to the 1Ds3. There may be other factors involved, but  I was struck by how smooth the gradients had become. But then I am also one of the unhappy few who can sometimes see the increase in noise from underexposing by 1/3rd EV. Let's call it a curse ...

But quantization precision (bit depth) is only marginally relevant to the ETTR concept, which is all about improving the S/N ratio in all tonal areas of the image. That also means that relatively low scene contrast offers the best potential because an averaging metering will technically 'underexpose' the highlights more and offer some headroom. A high contrast scene will only add a dilemma about how much of the specular highlights we can sacrifice to keep the exposure level at the mid- and lower tones as high as possible. In that case bracketing may be the best solution if the scene dynamics allow.

Cheers,
Bart
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Ray

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Re: Better than ETTR ?
« Reply #41 on: August 08, 2011, 08:05:52 am »

Unfortunately there is absolutely no easy way to use EttR with current cameras.  You have to shoot, examine histo, and adjust (and your guessing at that because the histo isn't telling you enough about the raw data).

That's not quite true, Wayne. There is a reasonably easy way of using ETTR without experimenting first with a shot then examining the histogram.

Set the camera to spot meter mode and full manual mode. Take a reading of what you see as the brightest part of the scene, for example a white cloud, a blue sky, a galvanised iron roof, a white wall, a white shirt etc., then increase exposure by a certain number of stops depending on the model of camera.

As I recall with my Canon 5D, that increase was 3 stops which is easy to calculate. With some makes of camera it might be 2.5 stops, slightly more difficult to calculate.

I also recall being amazed at how accurate this method could be. But again it's not ideally suitable when a shot has to be taken quickly to capture the moment. For this reason I haven't persevered with the method, but I think with practice one could get to the stage of being very quick and accurate in locating the brightest part of a scene and making the necessary exposure increase with one's thumb on the wheel without moving the camera from one's eye.
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digitaldog

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Re: Better than ETTR ?
« Reply #42 on: August 08, 2011, 10:32:08 am »

I don't think anyone suggests that EttR has replaced aperture/shutter speed/ISO as the priority settings in determining an exposure.  All that is suggested is that an exposure based on EttR often will leave you with better raw data than the setting chosen by your camera, if you have the headroom and don't have to compromise those other areas.

Exactly! Whenever we run into these ETTR discussions, some post theoretical problems with the practice (like this one concerning DOF), or how it clips highlights (not highlights you want to retain IF you ETTR correctly) or how people will now ruin their images due to slower shutter speeds to gain more exposure. Its as if suggesting ETTR implies all the aspects of sound image capture we’ve been practicing for 100+ years is to be ignored or isn’t valid any longer. ETTR is about idealized exposure for raw data when you have the time and desire for idealized data, all other photographic practices still in effect.
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Andrew Rodney
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fike

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Re: Better than ETTR ?
« Reply #43 on: August 08, 2011, 11:08:57 am »

My experience with EttR has been mixed.  I have found that sometimes when I have a very narrow dynamic range (flat light), I can make a crummy lighting situation better by having more levels in the high range to be stretched in post processing. 

On the other hand, I find more frequently that I don't like the results (particularly in skies). Sometimes this is because I have used the luminance histogram and missed the fact that I actually clipped one of the channels and not the others.  This often creates unattractive cyan highlights in skies...yes, yes, I was too aggressive with EttR. I know that, but it can be easy to miss if you don't do some substantial experimenting with exposure and the RGB and luminance histogram. 

When you have time, photographers should substantially underexpose the image to see if there are any spikes way off to the right of the graph.  Of course, we should be able to see this with our eyes, but generally too much dallying around means you miss the shot. 

As a woodland photographer, shadows are key, but perhaps more key is not blowing out the very small areas of light filtering between leaves.  I have learned to accept that sometimes blacks are a part of the image.  Going to extremes to rescue detail in those blacks doesn't always enhance the image particularly if I find very small highlights blooming in the branches of the trees.  Yes, again I recognize that I was too aggressive with EttR, but this is my main point that when I have used EttR in woodland photography, I very frequently blow the shot with EttR. 

I think someone said it above...If the dynamic range of the image exceeds the dynamic range capability of the camera (always in woodlands photography) then EttR doesn't help.  When dynamic range is less than the range of the camera, EttR can vastly improve an image.  The trouble is that in the moment of capture, it can be easy to misjudge these things.
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Ray

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Re: Better than ETTR ?
« Reply #44 on: August 08, 2011, 11:53:47 am »

Its as if suggesting ETTR implies all the aspects of sound image capture we’ve been practicing for 100+ years is to be ignored or isn’t valid any longer. ETTR is about idealized exposure for raw data when you have the time and desire for idealized data, all other photographic practices still in effect.

If you have the time and desire for idealised data, there should be no problem at all in this digital age. Michael in his recent article on the topic of ETTR was lamenting the fact that manufacturers have not yet designed a camera that will guarantee an automatic ETTR. That's where the difficulty lies, when you might miss the shot due to the time it takes to work out the settings for an idealised exposure.
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digitaldog

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Re: Better than ETTR ?
« Reply #45 on: August 08, 2011, 12:23:40 pm »

Michael in his recent article on the topic of ETTR was lamenting the fact that manufacturers have not yet designed a camera that will guarantee an automatic ETTR.

If they would even make an attempt, provide a useful histogram I’d be happy. I’m not expecting any guarantees, just an effort.
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Andrew Rodney
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ErikKaffehr

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Re: Better than ETTR ?
« Reply #46 on: August 08, 2011, 04:50:14 pm »

Hi,

After reading Michael's original article on ETTR my approach has been to maximize the exposure, using the histogram. Fortunately enough the Sony's I have now have both RGB and luminance histograms and blinking zones for over and under exposure. I essentially found both quite reliable.

In my view ETTR means is that we try to utilize the full histogram, thus essentially optimizing available DR and minimizing noise relative to signal. So I don't really see how the DR of the subject matters, whatever the tonal range of the subject we want a "full histogram without clipping".

For me, ETTR essentially mean that we don't care about the placement of midtones, because that will be done later in postprocessing. Quite obviously, DR is maximal at minimum ISO, and that is what I essentially always use when possible. My experience has been that DR is almost never an issue for me, except perhaps when shooting inside building and wanting to handle shadows detail and window detail. In those situation I'd say HDR may be a good recourse.

I started do some more testing on ETTR after reading Michaels article, but essentially found that I get into clipping if I try to move outside the in camera histogram.

I'd also say that i absolutely concur with Michael's suggestion for an ETTR option on modern cameras. Especially on modern EVIL cameras it should really be a piece of cake. On the other hand I guess that most of the processing in the cameras is done in the ASICs (Application Specific Integrated Circuit) and additional functionality may not always be easy to add.

Best regards
Erik


My experience with EttR has been mixed.  I have found that sometimes when I have a very narrow dynamic range (flat light), I can make a crummy lighting situation better by having more levels in the high range to be stretched in post processing. 

On the other hand, I find more frequently that I don't like the results (particularly in skies). Sometimes this is because I have used the luminance histogram and missed the fact that I actually clipped one of the channels and not the others.  This often creates unattractive cyan highlights in skies...yes, yes, I was too aggressive with EttR. I know that, but it can be easy to miss if you don't do some substantial experimenting with exposure and the RGB and luminance histogram. 

When you have time, photographers should substantially underexpose the image to see if there are any spikes way off to the right of the graph.  Of course, we should be able to see this with our eyes, but generally too much dallying around means you miss the shot. 

As a woodland photographer, shadows are key, but perhaps more key is not blowing out the very small areas of light filtering between leaves.  I have learned to accept that sometimes blacks are a part of the image.  Going to extremes to rescue detail in those blacks doesn't always enhance the image particularly if I find very small highlights blooming in the branches of the trees.  Yes, again I recognize that I was too aggressive with EttR, but this is my main point that when I have used EttR in woodland photography, I very frequently blow the shot with EttR. 

I think someone said it above...If the dynamic range of the image exceeds the dynamic range capability of the camera (always in woodlands photography) then EttR doesn't help.  When dynamic range is less than the range of the camera, EttR can vastly improve an image.  The trouble is that in the moment of capture, it can be easy to misjudge these things.
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douglasf13

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Re: Better than ETTR ?
« Reply #47 on: August 08, 2011, 07:13:00 pm »

As Ken mentioned in the other thread, what about color issues when you expose mid tones too far right?

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Bart_van_der_Wolf

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Re: Better than ETTR ?
« Reply #48 on: August 08, 2011, 08:02:55 pm »

As Ken mentioned in the other thread, what about color issues when you expose mid tones too far right?

Hi Douglas,

Mid-tones shouldn't be a problem with a good Raw converter. With Adobe ACR or Lightroom it can apparently depend on the camera profile. Of course when you clip too much of the highlight data, it may be impossible to reconstruct the highlight color.

Cheers,
Bart
« Last Edit: August 08, 2011, 08:09:49 pm by BartvanderWolf »
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douglasf13

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Re: Better than ETTR ?
« Reply #49 on: August 08, 2011, 08:19:55 pm »

  Andrey Tverdokhleb and Iliah Borg, the developers of Raw Photo Processor, say color is very much an issue when exposing past mid tones, at least with most newer cameras. To quote Andrey in reference to the Sony A900 on another forum:

"No, I meant using camera light meter (or external one if you care), but don't push histogram to the right and use camera light meter as it's intended, i.e. expose most important part of a picture around camera midpoint.  ETTR had some reasons for old cameras with low DR - noise was too close to the midpoint and we had to do this to minimize it. With late cameras which have over 9 stops of DR ETTR is very harmful for colors - midpoint is the most colorful place in A900 gamut and noise is not an issue there any more. In A900 gamut slowly narrowing down from midpoint to shadows and very quickly narrowing down from midpoint to highlights. This means that brightest stop of the camera range has most of colors gone forever and they cannot be restored with negative exposure compensation. I'd say all color critical parts should be below top 1.5 stops. Veiling glare from lens and sensor are the culprits here."

"Squeezing scene with high DR into sensor or film range is a totally valid approach when needed, same as exposing for shadows. ETTR however assumes that it's always better to shift histogram to the right, even when your scene is only 6 stops wide and sensor is 9.5 stops wide. You probably already noticed before that slightly underexposed shots can be amazingly colorful even after exposure correction and I definitely noticed that ETTR shots can be very dull after correction even if there was no clipping. So my point is that ETTR is not always better and shouldn't be used unconditionally. The whole approach that you need to pay attention only to highlights is very limiting - what's really important is were we place critical part of a picture on a sensor range. This critical part can be anywhere - in shadows, highlights or in the middle and we should understand that moving it closer to the middle gray will improve it's appearance and try our best. That's it "

"Regarding ETTR I already mentioned this, but let me rephrase - ETTR as universal approach for all kinds of shooting is wrong and unfortunately most of people treat it this way no matter what and how they shoot. It's easy to understand and there is even some technical explanation behind it, but in fact it doesn't tell the whole story. ETTR as approach when we are trying to open shadows without clipping highlights is a valid technique when needed and as long as we understand what we gain and what we loose there is absolutely nothing wrong with that."


Iliah and Andrey have managed to put together a converter with better output than most of the other expert's converters, and I find their opinion compelling on this issue of ETTR.
« Last Edit: August 08, 2011, 08:24:36 pm by douglasf13 »
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marcmccalmont

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Re: Better than ETTR ?
« Reply #50 on: August 08, 2011, 08:56:26 pm »

Are there any graphs published that show gamut vs level at various iso's? to both confirm this and optimize your exposure?
Marc
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Marc McCalmont

Ray

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Re: Better than ETTR ?
« Reply #51 on: August 08, 2011, 10:06:35 pm »

In my view ETTR means is that we try to utilize the full histogram, thus essentially optimizing available DR and minimizing noise relative to signal.

Erik,
I think we should distinguish between the two types of camera designs regarding higher-than-base ISO performance, and between the two methods of shooting regarding available time to plan the shot and use tripod.

With the D7000 and a few other models, including most MFDBs I think (at least the older models), there is actually only one concern regarding attempts to achieve that 'idealised amount of RAW data', as Andrew put it, and that concern is overexposure at base ISO.

This simplifies the ETTR situation significantly for hand-held shots and/or moving subjects whenever it's clear that the desired combination of shutter speed and aperture in the available light requires an increase in ISO.

With Canon cameras, an ETTR at ISO 400 produces a better SNR than the same shot showing an underexposure of 2 stops at base ISO. With the D7000 it doesn't, not because ISO 400 is worse on the D7000, but because ISO 100 is better.

In such circumstances, there is no need to 'try to utilize the full histogram' as you put it. One can happily shoot all day in manual mode at base ISO and be completely free of any obsession with ETTR. The only concern is overexposure, and shutter speed can easily be changed without moving the camera from one's eye.

As I recall, the first DSLRs that were available had a rather poor DR compared with negative film, and especially B&W film. This factor, in combination with a digital sensor's lack of the smooth roll-off or toe which is characteristic of film, created problems for the first DSLR users, of a lack of 'headroom' regarding exposure.

Attempts to maximise the DR in the capture would often lead to the clipping of at least one color in the highlights. Playing it safe could result in disturbing noise in the shadows and lower midtones.

In my view we no longer have to be so obsessive about ETTR when using modern DSLRs, not just because the DR and SNR characteristics of modern DSLRs are much improved, but also because memory is now so cheap.

When in doubt, bracket exposure, or bracket ISO in circumstances where there is a risk that the 'overexposed' shot, which may turn out to be the ideal exposure, has too slow a shutter speed to freeze movement.

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Schewe

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Re: Better than ETTR ?
« Reply #52 on: August 09, 2011, 12:17:53 am »

"Regarding ETTR I already mentioned this, but let me rephrase - ETTR as universal approach for all kinds of shooting is wrong and unfortunately most of people treat it this way no matter what and how they shoot. It's easy to understand and there is even some technical explanation behind it, but in fact it doesn't tell the whole story. ETTR as approach when we are trying to open shadows without clipping highlights is a valid technique when needed and as long as we understand what we gain and what we loose there is absolutely nothing wrong with that."

I have no problem with the above...I don't suggest ALWAYS doing ETTR...only when it's appropriate. But, I don't really agree with the warnings regarding color. I've not experienced that with ACR/LR. Course, I'm pretty good at adjusting both tone and color with both. Can't comment on Raw Photo Processor cause I've never used it...maybe it's more of a problem for Raw Photo Processor than ACR/LR?

Look, if you know what you are doing, you'll know when and how to use ETTR...if you don't, go right ahead and flail about like regular people and leave image quality on the table–you're choice.
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Ray

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Re: Better than ETTR ?
« Reply #53 on: August 09, 2011, 12:42:24 am »

But, I don't really agree with the warnings regarding color. I've not experienced that with ACR/LR.

Nor have I, and I agree that such issues depend on one's skill with ACR adjustments and post processing in Photoshop.

For example, I find it easier to create a dramatic sky in post processing if I've underexposed the sky at least a little, probably because I need more skill with Photoshop.

I can also appreciate that it may be the case if just one channel has been clipped in a highlight area, even in small parts of the area, and reconstruction of that clipped channel has taken place in ACR, then the colors may be slightly different as a consequence.

The most obvious example I can think of is a blue sky where the red channel is partially clipped. The result is a sky that can look more cyan than it should.
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Guillermo Luijk

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Re: Better than ETTR ?
« Reply #54 on: August 09, 2011, 03:50:25 am »

The most obvious example I can think of is a blue sky where the red channel is partially clipped. The result is a sky that can look more cyan than it should.
It's difficult that the red channel clips in the RAW file. If it does, the green channel will be clipped as well most of the times. So surely if the red channel got clipped and not the green channel, it happened at post processing.

This scene:


had the following RAW histogram, where the green channel was more than 1 stop ahead of the red channel:

(Medición puntual = spot metering)

A Canon 5D was used to spot meter the higlights of the scene. The RAW histogram shows at least 3 stops of headroom before saturation.

More spot metering examples here.
« Last Edit: August 09, 2011, 03:56:18 am by Guillermo Luijk »
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Ray

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Re: Better than ETTR ?
« Reply #55 on: August 09, 2011, 06:48:02 am »

It's difficult that the red channel clips in the RAW file. If it does, the green channel will be clipped as well most of the times. So surely if the red channel got clipped and not the green channel, it happened at post processing.


You may be right. When the sky turns to cyan, both the red and green channels may be clipped, but I get the impression the red channel may be clipped first, or to a greater degree.

Here's an image of a temple in Kathmandu, with blown sky. The sky is brighter on the right, and more blown. Taking readings from the left-hand corner I get values of 134, 151, 197.

From the right-hand corner, I get readings of 207, 227, 251. The percentage of red on the left is greater, but also the percentage of green. The percentage of blue on the right is greater.  However, the reduction of the percentage of red on the right is greater than the reduction in the percentage of green.
« Last Edit: August 09, 2011, 07:05:32 am by Ray »
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Guillermo Luijk

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Re: Better than ETTR ?
« Reply #56 on: August 09, 2011, 09:23:29 am »

Taking readings from the left-hand corner I get values of 134, 151, 197. (...)

Readings from the RAW developer are irrelevant, you don't know what happened to your RAW values before they were displayed (exposure correction, white balance, highlight (recovery) strategies,...). Just open your RAW file into Rawnalyze and inspect the genuine RAW histograms to find out.

A RAW developer is not a tool suited to analyze RAW files, it is a tool designed to develop them.

Regards
« Last Edit: August 09, 2011, 09:25:14 am by Guillermo Luijk »
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fike

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Re: Better than ETTR ?
« Reply #57 on: August 09, 2011, 09:27:53 am »

Skies shifting towards cyan is my major problem with EttR.  Of course this means that I did EttR WRONG, but regardless it is an occupational hazard of the strategy that you will occasionally misjudge and clip one color channel while the general luminance histogram looks pretty good.
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Eric Myrvaagnes

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Re: Better than ETTR ?
« Reply #58 on: August 09, 2011, 09:32:06 am »

Look, if you know what you are doing, you'll know when and how to use ETTR...if you don't, go right ahead and flail about like regular people and leave image quality on the table–you're choice.
That sums it up perfectly for me. Thanks, Jeff.
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Ray

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Re: Better than ETTR ?
« Reply #59 on: August 09, 2011, 10:02:32 am »

Readings from the RAW developer are irrelevant, you don't know what happened to your RAW values before they were displayed (exposure correction, white balance, highlight (recovery) strategies,...). Just open your RAW file into Rawnalyze and inspect the genuine RAW histograms to find out.

A RAW developer is not a tool suited to analyze RAW files, it is a tool designed to develop them.

Regards


That's true. I don't know what happens to my RAW files before they are displayed. I get the impression that attempts are made by ACR to reconstruct any clipped channels. In the case of grey clouds, I believe even greater reconstruction of clipped channels is possible.
However, the fact is that ACR and Photoshop are the programs I use to develop my images. I don't see much advantage in using one program to analyse my RAW images and another program to develop them.
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