Luminous Landscape Forum

Equipment & Techniques => Digital Cameras & Shooting Techniques => Topic started by: dtrayers on May 01, 2006, 10:38:05 pm

Title: Today's DSLR should have another exposure mode
Post by: dtrayers on May 01, 2006, 10:38:05 pm: I shoot dance and theater and the dynamic range of the scenes can be a challange for the meter of my 1DmkII. I've experimented with all four metering modes and I've found that in the changing light conditions of the stage that more often than not, evaluative works the best. I do have to dial in a bit of exposure compensation to keep the highlights from blowing out, but it can vary based on the costume of the subject and the lights. Lots of hard light with light skin and/or light costumes need more negative exposure comp than a less contrasty scene. Makes sense, but hard to do in practice. At the high ISO's I shoot, I don't want to underexpose which will accentuate the noise, but I definitely don't want to overexpose.

But over the weekend as I was shooting for a local non-profit dance studio, it dawned on me that a very useful variation of the evaluative metering mode would be a 'no-clipping' option. The camera would evaluate all the metering zones and then based on the measurements calculate the exposure such that the brightest zone would be just short of clipping, or 'exposed to the right'.

It would be a kind of "automatic" exposure compensation. It would only really work for the evaluative mode where the camera would evaluate 21 areas and pick the one to expose on.

For digicams that offer a live histogram, the same concept could be used to calculate exposure, only instead on relying on 21 metering zones, the camera could use the actual histogram and calculate exposure such that the histogram is 'exposed to the right'.
Title: Today's DSLR should have another exposure mode
Post by: Peter Jon White on May 01, 2006, 11:15:20 pm: The idea has been floating around for quite a while. And I'm surprised that no company, as far as I know, has implemented it in some fashion. Of course there would have to be a way of adjusting a threshold of some sort. Some highlights you don't care about blowing. A spot of sunlight reflecting off of the chrome trim of an automobile, or sunlight on water can and should be blown, otherwise you'll have nothing but noise when you're adjusting the exposure later. But it should be possible to do. And since highlights are the key to optimum digital exposure, the ideal metering system should be looking at highlights.
Title: Today's DSLR should have another exposure mode
Post by: Sheldon N on May 01, 2006, 11:28:08 pm: I think Peter has hit the nail on the head with the issue of the "threshold". The difficulty would be that the variability of that highlight you are trying to save detail in may be 5 or 10 stops.

One example I've seen is in the impementation of the Canon ETTL-II flash system. It is sensitive to reflective items in the photo, cutting flash output to try and prevent highlight details from blowing out. You can see this by taking a picture in a mirror. If the flash head is visible in the shot, the system intervenes drastically cutting output by 3-4 stops to try to save the detail in the flash head.

Using your example of a shooting dancers in a theatre, the camera would have to make an intelligent choice about whether you were trying to capture highlight detail in the dancer's costume (at 3 stops over) or if you were trying to capture detail in the spotlight you accidentally included in the frame (at 20 stops over). There may not be a consistent threshold to use, and the incorrect choice could give you an unuseable shot.

To me, the real problem is not that the highlights clip, it's that they look so bad when they do so!
Title: Today's DSLR should have another exposure mode
Post by: Schewe on May 02, 2006, 12:23:31 am: The irony is that in a digital sensor, you have, in effect, a -REAL- accurate (and real expensive) light measuring device since the whole sensor is a photon counter...

The way I see it, a half push of the shutter release could lock onto both auto-focus while at the same time shooting a non-recorded sensor capture that would evaluate every pixel in the capture and choose the optimal real capture exposure. A function button could lock the exposure setting until you hit the button again to release and re-meter...

This would be particularly useful to have the camera TELL YOU the scene dynamic range (assuming the camera makers would finally get real and adopt a standard). Then you could dial in a compensation factor based upon whether you want to bias the exposure to the shadows or the highlights-in the case where the scene is beyond the dynamic range.

Unfortunately, camera makers still seem to want to put in a separate light measuring device-a meter-when the real light measuring device should be the sensor itself.

Just a thought...
Title: Today's DSLR should have another exposure mode
Post by: bjanes on May 02, 2006, 09:58:26 am: Quote
The irony is that in a digital sensor, you have, in effect, a -REAL- accurate (and real expensive) light measuring device since the whole sensor is a photon counter...

The way I see it, a half push of the shutter release could lock onto both auto-focus while at the same time shooting a non-recorded sensor capture that would evaluate every pixel in the capture and choose the optimal real capture exposure. A function button could lock the exposure setting until you hit the button again to release and re-meter...

This would be particularly useful to have the camera TELL YOU the scene dynamic range (assuming the camera makers would finally get real and adopt a standard). Then you could dial in a compensation factor based upon whether you want to bias the exposure to the shadows or the highlights-in the case where the scene is beyond the dynamic range.

Unfortunately, camera makers still seem to want to put in a separate light measuring device-a meter-when the real light measuring device should be the sensor itself.

Just a thought...
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Jeff's suggestion makes a lot of sense, but of course it has not been implemented.

However, some progress is being made. I'm not familiar with Canon metering, but the Nikons have a CCD for metering that contains 1005 cells (alternating RGB) arranged in 15 rows and 67 columns covering virtually the entire frame. This sampling is not as extensive as Jeff suggests, but can be done in real time without pre-exposure. It should give the camera a good indication of the dynamic range and color content of the scene and probably could be put to better use for pre-exposure evaluation by the user and in evaluative metering.

One constant complaint of D70 users was "underexposure"--i.e. the camera refused to expose to the right in a high dynamic range scene. Apologists said this was to protect the highlights, but it made absolutely no sense to have images with the brightest stop of the histogram completely unpopulated. It was quite frustrating for advocates of ETTR. I suspect the exposure algorithm was adapted from their film cameras and not really appropriate for digital. However, the D200 in its matrix evaluative mode is much better--one has to override the camera much less often in order to expose to the right. For once, Nikon has listened to its users.
Title: Today's DSLR should have another exposure mode
Post by: Tim Gray on May 02, 2006, 11:40:24 am: Live histograms are likely not that far off (my recollection is that it's already implemented on at least 1 dslr).

I suspect it would be fairly easy to dial in a % permissible clipping, either highlights or shadows.

As an interim step, I'd like more accurate RAW based histograms (even if only after the shot). I often find that my brackets are not required and even if the histogram showed clipping at the time of the shot in the RAW image there is actually no clipping.
Title: Today's DSLR should have another exposure mode
Post by: sergio on May 02, 2006, 12:22:45 pm: It can help to know your sensor range. My 1DsMII for example goes up to + 2 2/3 stop and can recover 1 more stop (most of the time) in ACR making my usable range to + 3 2/3 of a given tone spot metered to normal exposure.

I carry a spot meter because of the inaccuracy of the histogram. In many shot it won't matter much, but in high contrast scenes you just need the last bit of usable range you can get to expose correctly to the right, to have nice clean shadows.
Title: Today's DSLR should have another exposure mode
Post by: bjanes on May 02, 2006, 01:24:43 pm: Quote
It can help to know your sensor range. My 1DsMII for example goes up to + 2 2/3 stop and can recover 1 more stop (most of the time) in ACR making my usable range to + 3 2/3 of a given tone spot metered to normal exposure.

I carry a spot meter because of the inaccuracy of the histogram. In many shot it won't matter much, but in high contrast scenes you just need the last bit of usable range you can get to expose correctly to the right, to have nice clean shadows.
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I agree with Tim Grey (above) that a raw based histogram would be useful, and it should not be white balanced. Sergio is taking great pains to expose to the right, but with both Canon and Nikon digital SRLs with daylight exposure, the output of the red and blue channels is considerably (about 1 stop) less than the green, and this is not shown on the camera histogram. During conversion, a multiplier is applied to the blue and red channels to equalize them with the green.

The green channel histogram may be exposed properly to the right, but the blue and red fall short of the right. One way to balance the channels and gain better dynamic range is to use a cc100M filter over the lens to hold back the green light and equalize the channels. One then performs white balance with the filter in place and the blue and red multipliers then approach unity. One can gain up to 1 stop of DR with this technique. Here is an example of an unfiltered daylight exposure for the D200:

[attachment=533:attachment]

For some images showing this effect with the D200 and EOS 1D Mark II see this thread in the Adobe Camera Raw forum:

[a href=\"http://www.adobeforums.com/cgi-bin/webx?14@@.3bb6a85c.3bbf0e1d/10]http://www.adobeforums.com/cgi-bin/webx?14...85c.3bbf0e1d/10[/url]

I originally learned of this technique from a post on the DPReview forum by Julia Borg.
Title: Today's DSLR should have another exposure mode
Post by: Ben Rubinstein on May 02, 2006, 02:32:12 pm: in high contrast situations you can easily hold the highlights from clipping while horribly underexposing your subject. Backlighting would be a good example and probably pretty relevent to your stage shooting. If you have a scene with a lot of white the camera would hold the whites and but the midtones would underexpose. The trick with digital is to decide where you want the highlights, sometimes you have to blow highlights for a good exposure. An ETTR metering mode would cause underexposure in too many situations.

There just isn't enough DR in the highlights with digital to always capture a high contrast scene in one frame which is why HDR gives such great noise, it uses the ETTR for each level of the brightness so you have the maximum information, not only in the highlights but in the shadows too. ETTR is better for the shadows than not doing so, and far better for low contrast scenes, but it is only part of the technique needed to capture the full range of a scene with good quality. At a certain level of contrast ranges you need more than one exposure or you need to work out and understand what highlights you don't mind sacrificing for cleaner midtones.
Title: Today's DSLR should have another exposure mode
Post by: DiaAzul on May 02, 2006, 02:50:15 pm: Quote
Unfortunately, camera makers still seem to want to put in a separate light measuring device-a meter-when the real light measuring device should be the sensor itself.

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You are always going to have a two sensor (metering and capture) solution whilst manufacturers retain the current capture sensor design. It is just not feasible to have a live capture type metering with, say, Canon's CMOS sensor design. This is part of the reason for having the two sensors separate. I also suspect that the metering sensor has a greater dynamic range compared with the capture sensor to provide the 0-20ev range that is required to accurately meter a scene. If you do go for an all in one design then the capture sensor would need to have a 0ev to 20 ev dynamic range which is not yet economically realistic, but in 2-5 years may be the panacea that all photographers are looking for.

This doesn't preclude, though, metering sensors with larger numbers of pixels (like Nikon's) and the ability through that type of sensor to provide a live histogram, preferably as an overlay in the viewfinder. However, this may ultimately come down to market demand balanced up against the costs of implementing such a solution.

My point and squirt (Panasonic FX-01) provides live histogram, which is useful given its propensity to clip highlights - though as reviews have pointed out the dynamic range is not great and the sensor is noisier than most would prefer. Having a similar feature on my DSLR would be a welcome addition to existing metering modes - though in reality I can cope quite well with the tools I have at the moment provided a certain amount of learning experience is factored into adjustments and RAW is used to provide additional latitude in the post processing.
Title: Today's DSLR should have another exposure mode
Post by: jd1566 on May 05, 2006, 11:50:03 am: dtrayers, excellent suggestion. Why don't you contact Chuck Westfall of Canon USA about it. He seems to be their ear to the ground on user suggestions. He writes a monthy article/response to users'questions and suggestions, and is generally a good source of information if you are having problems with something Canon.

http://dirckhalstead.org/issue0604/westfall.html (http://dirckhalstead.org/issue0604/westfall.html)

At the bottom of the article there is a link to his e-mail.
Title: Today's DSLR should have another exposure mode
Post by: Anon E. Mouse on May 06, 2006, 03:48:16 am: I think the answer is what the answer has always been. The photographer needs to learn how to expose correctly for the equipment and the situation. Machines cannot make subjective decisions which is what good exposures are based on in complex situations. No silver bullet here, I am afraid.

I am not sure a RAW histogram has any practical value as it would be difficult to evaluate unless you convert it first (which is what RAW processing previews do anyway). Also displaying RAW data is not possible either - which is why a thumbnail file must be created so you can preview the image on the camera. Even if you could display the RAW data, it would be hard to evaluate the image as it is not easy to equate it to the converted data (and forget about white balance).
Title: Today's DSLR should have another exposure mode
Post by: Jonathan Wienke on May 07, 2006, 06:43:05 pm: A RAW histogram would be trivially simple to implement. You wouldn't need to do any Bayer interpolation, white balance adjustments, or any color processing whatsoever. Simply create a bar graph with 32 segments from left to right (32 vertical bars going left to right) with each bar representing 1/3 stop of exposure. The rightmost bar should be red, and its height should represent the number of clipped pixels in the RAW data. The next two bars should be yellow, and their heights represent pixels that are within 1/3 stop of clipping, and between 2/3 and 1/3 of a stop from the clip value, respectively. The remaining bars should represent successively decreasing 1/3-stop exposure intervals, with the leftmost bar or three colored yellow to indicate the possibility of increased noise levels in those exposure levels. A simple lookup table in the camera firmware would suffice to indicate which bar any given RAW value should be assigned, to make the 1/3 stop per bar paradigm work properly. This would require far less firmware programming than the current converted RAW-to-JPEG bastardgram, work perfectly with any sensor regardless of whether it was Bayer-pattern or monochrome, and indicate to the user the exact exposure adjustment necessary to achieve ideal exposure with a single "polaroid" exposure test shot. What's not to like?
Title: Today's DSLR should have another exposure mode
Post by: bjanes on May 07, 2006, 10:40:22 pm: Quote
A RAW histogram would be trivially simple to implement. You wouldn't need to do any Bayer interpolation, white balance adjustments, or any color processing whatsoever.

What's not to like?
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I was thinking along the same lines. What Jonathin says is quite true, but I'm not certain how useful raw histograms would be.

On the Adobe Camera Raw forum I once suggested that a raw histogram would be useful, but Bruce Fraser said that it would not be very helpful because, with linear data, all of the data are to the left of the histogram. I wasn't convinced until I did some testing.

Here is a shot of a red flower in which the red channel appears blown as shown in the ACR preview with sRGB:

[attachment=548:attachment]

However, with ProPhotoRGB the red channel is no longer blown:

[attachment=549:attachment]

Here is the raw histogram from the DCRaw conversion:

[attachment=550:attachment]

The raw histogram shows that no channel is blown, but is indeed hard to interpret just like Bruce said it would be. Comments are welcome.
Title: Today's DSLR should have another exposure mode
Post by: BernardLanguillier on May 09, 2006, 05:08:33 am: Even if we keep the current metering devices of the cameras, it would still be highly valuable to have some form of automatic expose to the right double exposure:

- first exposure is done based on camera metering device, in a way as to fully capture the non specular highlights,
- second exposure is over-exposed enough compared to the first one so as to get non clipped non specular highlights (based on true RAW histogram data) while fully using the available DR.

The problem is that

- companies like Canon and Nikon just won't release half cooked cumbersome functions, even if they were potentially very useful to knowledgeable users...
- the resulting images would be over-exposed, and would require the typical expossed the right images post-treatment -> many users would complain that the thing doesn't work well,
- ...

Cheers,
Bernard
Title: Today's DSLR should have another exposure mode
Post by: John Sheehy on May 22, 2006, 11:04:23 pm: Quote
The raw histogram shows that no channel is blown, but is indeed hard to interpret just like Bruce said it would be. Comments are welcome.

What is hard about it? The last half is one stop, the quarter to the left of that is another stop; the eight to the left of that is another; the histogram could have dark lines for stops, and thinner lines for 1/3 stops.

That shot should have been taken with 1.3 stops more exposure with almost no clipping, and 2 stops with light clipping, even if it took a higher ISO to do so.

The problem, however, is that most RAW converters don't understand exposing to the right. Setting the Exposure slider in ACR to -2, for example, does not necessarily divide the RAW data by 4, as you'd expect. It may do that to the midtones, but the highlights might be divided by quite less, distorting the transfer curve of RAW to RGB.
Title: Today's DSLR should have another exposure mode
Post by: Serge Cashman on May 22, 2006, 11:36:12 pm: Somehow I get an impression you guys are talking about the exposure to the LEFT. "Just make sure highlights are not blown (an unrealistic demand in most cases, especially in the low light situations) and push everything else to the left".

Exposing to the right is supposed to take advantage of the fact that most of the bits in a RAW file are dedicated to the highlights... Which is unfortunate cause sensors don't really capture that many details in highlights in the first place, no matter how many bits are dedicated to them.

The idea of ETTR is to squeese as many details as possible into shadows by moving everything else to the right as far as possible, not to push the shadows out of the picture based on highlights (by moving everything else to the left).
Title: Today's DSLR should have another exposure mode
Post by: dlashier on May 22, 2006, 11:37:35 pm: Quote
The problem, however, is that most RAW converters don't understand exposing to the right. Setting the Exposure slider in ACR to -2, for example, does not necessarily divide the RAW data by 4, as you'd expect. It may do that to the midtones, but the highlights might be divided by quite less, distorting the transfer curve of RAW to RGB.

C1 does this quite well, at least with the 1 stop EC's I measured. (http://www.lashier.com/home.cfm?dir_cat=26537). IIRC I did a similar test with ACR and it also did ok.

- DL
Title: Today's DSLR should have another exposure mode
Post by: Serge Cashman on May 22, 2006, 11:53:54 pm: As far as live histogram - you either need two separate sensors or not an SLR. Both of which exist already.
Title: Today's DSLR should have another exposure mode
Post by: John Sheehy on May 23, 2006, 08:31:34 am: Quote
Exposing to the right is supposed to take advantage of the fact that most of the bits in a RAW file are dedicated to the highlights... Which is unfortunate cause sensors don't really capture that many details in highlights in the first place, no matter how many bits are dedicated to them.

What are you basing that on?

The sensors capture highlight the best, right up to the saturation point at the lowest ISO, or RAW clipping point if that is lower, and at the higher ISOs. Perhaps you are defining highlights as the areas that sometimes clip? The whole point is getting the highewst exposure possible without clipping desired highlights. Clipping them is not "exposing to the right" properly.
Title: Today's DSLR should have another exposure mode
Post by: oldcsar on May 23, 2006, 03:06:42 pm: I've found that I can fudge an expose-to-the-right mode by selecting Aperture priority on my Rebel, and then stepping up my exposure compensation (by a fraction of a stop or a full stop, depending on the shutter speed that the camera decides and by how close it is to where I want it). I've found that my Rebel on Ap. Prior. mode generally makes a reasonable exposure in regards to preventing clipping on highlights (with exp. comp. at baseline), but I've found that the little bit of exposure compensation makes it JUST right for my purposes.
Title: Today's DSLR should have another exposure mode
Post by: Serge Cashman on May 23, 2006, 05:58:41 pm: Quote
What are you basing that on?
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If sensors were the best at capturing highlights up to the clipping point you'd be able to pull almost infinite high quality details out of the highlights just before they clip. I'm not an engeneer but it is definitely not what I can observe. The bits are there, the details are not.

"Just don't blow the highlights" exposure is really opposite to trying to shift everything to the right. "Desired" highlights is the key word here - you decide what to clip. I mean - if your image has a narrow dynamic range then of course just overexpose until highlights are about to blow, it should be technically possible at some point in the future to do it automatically... But that's not the case in a situation like described in the original post - it's not a narrow dynamic range.
Title: Today's DSLR should have another exposure mode
Post by: Ray on May 23, 2006, 11:18:47 pm: Quote
If sensors were the best at capturing highlights up to the clipping point you'd be able to pull almost infinite high quality details out of the highlights just before they clip. I'm not an engeneer but it is definitely not what I can observe. The bits are there, the details are not.

Almost infinite? I think you mean, 'the maximum detail the system can deliver in the shooting circumstances', don't you?

As I understand, the response of digital imagers is quite different to film in the sense that highlights in film undergo significant compression before total clipping, commonly known as a 'shoulder'.

Digital sensors have a much narrower shoulder. Within half a stop or so, it seems, you can go from a situation of full, uncompressed detail in the highlights to totally blown highlights. There's a much sharper cut-off which presents a major problem for ETTR. It's clearly better to be a 1/2 stop under the correct exposure for ETTR than a 1/2 stop over, if preserving those highlight details is important.

However, what I've just written is an oversimplification (how could it be otherwise. I'm not even sure I know what I'm talking about ). There's another issue relevant here, which is addressed in another current thread, 'expanding dynamic range'. It is unlikely that all 3 channels in a digital sensor are going to 'blow out' at at the same point. The red channel might blow out first, followed by the blue channel, leaving the green channel as pure luminance. It seems there is no way around this, other than to use the right type of filter in front of the lens and do a 'custom WB' before taking the shot.

Now, just how precise do you want to be in your photography?
Title: Today's DSLR should have another exposure mode
Post by: Serge Cashman on May 24, 2006, 12:33:40 am: Quote
Almost infinite? I think you mean, 'the maximum detail the system can deliver in the shooting circumstances', don't you?
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I was objecting to a description of contemporary sensors as exceptionally adapt at capturing extreme highlight details. Personally I think the sensors are not good at that whatsoever. So you seem to agree with me.

Still - the point of ETTR is overexposing as much as possible so you get the most bits possible dedicated to your image information. Not to measure the extreme highlights and push everything else to the left.
Title: Today's DSLR should have another exposure mode
Post by: jani on May 24, 2006, 09:32:32 am: Quote
I was objecting to a description of contemporary sensors as exceptionally adapt at capturing extreme highlight details. Personally I think the sensors are not good at that whatsoever. So you seem to agree with me.

Still - the point of ETTR is overexposing as much as possible so you get the most bits possible dedicated to your image information. Not to measure the extreme highlights and push everything else to the left.
This is a misrepresentation of the technique as described here on the LL and on other sites. I can see why you object to following a technique which is obviously in error, but it isn't ETTR you're describing.

It's not about detail, it's about sensor noise and artifacts, and you definitely shouldn't blow the highlights*:

Quote
The simple lesson to be learned from this is to bias your exposures so that the histogram is snugged up to the right, but not to the point that the highlights are blown. This can usually be seen by the flashing alert on most camera review screens. Just back off so that the flashing stops.

Now of course when you look at the RAW file in your favourite RAW processing software, like Camera RAW, the image will likely appear to be too light. That's OK. Just use the available sliders to change the brightness level and contrast so that the data is spread out appropriately and the image looks "right". This will accomplish a number of things. The first is that it will maximize the signal to noise ratio. The second is that it will minimize the posterization and noise that potentially occurs in the darker regions of the image.

If reading Michael's article isn't enough, maybe this article by Roger Cavanagh (http://www.rogercavanagh.com/helpinfo/28_exposeright-1.stm) can help.

*There are few rules without exceptions, and I'd just like to point out that there are some highlights that you might desire to blow, such as specular highlights.
Title: Today's DSLR should have another exposure mode
Post by: Ray on May 24, 2006, 11:47:53 am: There's no doubt that ETTR is the right thing to do for the best quality image. The problem is getting it right. Backing off till the 'blown highlight' warning stops flashing can result in underexposure in my experience. However, this result might be due to RAW converters getting better. I recall when I first started using the D60, I could recover about 2/3rds of a stop in BreezeBrowser. With the latest versions of ACR it seems to be about one and 2/3rds stops.

Consider the following image of a sunrise taken about 4 years ago on one of the rare occasions that I arose before the sun did. It's being converted into a very wide color space, ProPhoto RGB. Brightness and contrast have been taken to a minimum yet it looks as though I have seriously blown the red and green channels.

[attachment=599:attachment]

However, if I apply minus 1.5 EC, the apparently blown red and green channels are clearly not blown, as can be seen in the image below.

[attachment=600:attachment]

But what about the centre of the sun? That white spot is bigger than a mere specral highlight. Whatever the setting in ACR, it's 255,255,255, even with -4EC, which is okay by me. I'd expect the centre of the sun to be a blown highlight, but I was curious as to what a linear conversion would reveal and was very surprised to find that even that centre white spot does not seem to be blown. It's just a neutral white. The image appears to be actually underexposed by about 1/4 of a stop. That's close enough for me .

[attachment=601:attachment]
Title: Today's DSLR should have another exposure mode
Post by: Serge Cashman on May 24, 2006, 08:38:57 pm: Quote
This is a misrepresentation of the technique as described here on the LL and on other sites. I can see why you object to following a technique which is obviously in error, but it isn't ETTR you're describing.

It's not about detail, it's about sensor noise and artifacts, and you definitely shouldn't blow the highlights*:

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Well - reread the article. Pay extra attention to the rationale for the technique. It's about bits dedicated to the image data.

It's an overexposure technique geared towards heavy post-processing that benefits from extra bits dedicated to image information, not a guide to correct exposure.

"Don't blow highlights" is a disclaimer, so to speak. "We all know (or at least should by now)" that it's only realistic on narrow dynamic range images. Some highlights are born to be blown (as you've mentioned in your note) .

Quote:

"...Now of course when you look at the RAW file in your favourite RAW processing software, like Camera RAW, the image will likely appear to be too light. That's OK. Just use the available sliders to change the brightness level and contrast so that the data is spread out appropriately and the image looks "right"..."

[a href=\"http://www.luminous-landscape.com/tutorials/expose-right.shtml]http://www.luminous-landscape.com/tutorial...ose-right.shtml[/url]
Title: Today's DSLR should have another exposure mode
Post by: Serge Cashman on May 24, 2006, 08:57:06 pm: Quote
It's just a neutral white. ...
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Which means "blown" in colloquial English.
Title: Today's DSLR should have another exposure mode
Post by: John Sheehy on May 24, 2006, 11:38:00 pm: Quote
I was objecting to a description of contemporary sensors as exceptionally adapt at capturing extreme highlight details. Personally I think the sensors are not good at that whatsoever. So you seem to agree with me.

You seem to be reading things from me that I didn't write. I said that the range just below clipping of the RAW data is the highest quality recording range.
Title: Today's DSLR should have another exposure mode
Post by: John Sheehy on May 24, 2006, 11:45:33 pm: Quote
If sensors were the best at capturing highlights up to the clipping point you'd be able to pull almost infinite high quality details out of the highlights just before they clip. I'm not an engeneer but it is definitely not what I can observe. The bits are there, the details are not.

What are you basing this on?

Every experiment I've ever conducted shows that the upper ranges are the best; the noise is highest there, but the signal is even higher, so the S/N ratio is higher. There is less posterization of your upper tones, as well.

In fact, a super-low-contrast scene exposed with +2 to +3 EC at ISO 400 or 800 has less noise and better subject detail than an ISO 100 shot with 0 EC. All the time; every time. No exceptions noted.

Quote
"Just don't blow the highlights" exposure is really opposite to trying to shift everything to the right.

It's not the opposite; it's a different paradigm. It's a matter of what it is that you want to put all the way to the right.
Title: Today's DSLR should have another exposure mode
Post by: Serge Cashman on May 25, 2006, 12:11:22 am: Quote
It's not the opposite; it's a different paradigm. It's a matter of what it is that you want to put all the way to the right.
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I can agree with that. But the objective of not clipping highlights pushes everything else to the left. The objective of exposure to the right demands an intelligent compromise.

And obviously both of these methods are post-processing oriented.
Title: Today's DSLR should have another exposure mode
Post by: Ray on May 25, 2006, 04:43:38 am: Quote
Which means "blown" in colloquial English.
[a href=\"index.php?act=findpost&pid=66501\"][{POST_SNAPBACK}][/a]

Well perhaps I should have been less colloquial. In the linear conversion, the centre of the sun appears to be a neutral pale grey with values of 214,214,214, indicating that I could have given a fraction of a stop more exposure.

Technically there are no whites, only shades of grey. The palest shade of grey within our 24 bit color system is represented by the numbers 255,255,255. Isn't that correct?
Title: Today's DSLR should have another exposure mode
Post by: bjanes on May 25, 2006, 08:19:12 am: Quote
But what about the centre of the sun? That white spot is bigger than a mere specral highlight. Whatever the setting in ACR, it's 255,255,255, even with -4EC, which is okay by me. I'd expect the centre of the sun to be a blown highlight, but I was curious as to what a linear conversion would reveal and was very surprised to find that even that centre white spot does not seem to be blown. It's just a neutral white. The image appears to be actually underexposed by about 1/4 of a stop. That's close enough for me .

[attachment=601:attachment]
[a href=\"index.php?act=findpost&pid=66459\"][{POST_SNAPBACK}][/a]

Ray,

So that we can evaluate your findings, what software did you use for the linear conversion, and what settings did you use. Was white balance applied? What do you mean by linear conversion?
Title: Today's DSLR should have another exposure mode
Post by: Ray on May 25, 2006, 10:33:43 am: Quote
Ray,

So that we can evaluate your findings, what software did you use for the linear conversion, and what settings did you use. Was white balance applied? What do you mean by linear conversion?
[a href=\"index.php?act=findpost&pid=66534\"][{POST_SNAPBACK}][/a]

Bill,
I used the linear conversion option in BreezeBrowser. WB as shot would have been applied. All other settings at default. Not accurate enough?
Title: Today's DSLR should have another exposure mode
Post by: bjanes on May 25, 2006, 12:22:22 pm: Quote
Bill,
I used the linear conversion option in BreezeBrowser. WB as shot would have been applied. All other settings at default. Not accurate enough?
[a href=\"index.php?act=findpost&pid=66546\"][{POST_SNAPBACK}][/a]

I downloaded the trial version of BreezeBrowserPro. Obviously, I don't know the program, but I can not easily get it to display the actual raw file with no white balance, tone curve, or levels applied. My overexposed color checker looks overexposed in the preview but normally exposed in the conversiion.

I can use manual levels in postprocessing, but I am unable to determine how to display the actual data numbers in the raw file. Personally, I prefer DCRaw for this purpose. Have you tried it?

Bill
Title: Today's DSLR should have another exposure mode
Post by: Serge Cashman on May 25, 2006, 08:44:08 pm: Quote
In the linear conversion, the centre of the sun appears to be a neutral pale grey with values of 214,214,214,
[a href=\"index.php?act=findpost&pid=66528\"][{POST_SNAPBACK}][/a]

Oh. Then it's not blown Sorry for my remark.

I obviously assumed that "white" meant all 255s.
Title: Today's DSLR should have another exposure mode
Post by: Ray on May 25, 2006, 11:56:15 pm: Quote
I downloaded the trial version of BreezeBrowserPro. Obviously, I don't know the program, but I can not easily get it to display the actual raw file with no white balance, tone curve, or levels applied. My overexposed color checker looks overexposed in the preview but normally exposed in the conversiion.

I also had to download the trial version because my older version, which I haven't used for years, would not of course support 5D RAW images. Intitially I could not get the preview window to display the linear image as it should appear and often I would just get a black screen, so I assumed there was a minor bug or system incompatibility somewhere. Oddly enough, it appears to be working today as it should. Don't know whether the system just required a reboot or whether a 'ticking and unticking' of the 'tagged' box did it. Whatever, it's now fine. Below is a screen shot of the BB window.

[attachment=613:attachment]

What's interesting here is that the image is not nearly as red as my previous screen shot of a linear conversion, shown earlier in the thread, which was captured within Photoshop. I'm guessing here as to the reason. The linear conversion does not have an embedded profile. My working space is ProPhoto RGB, an extremeley wide gamut space. I did not assign a profile when opening the image in PS but for the purpose of posting on the net, did a conversion to sRGB. The redder image represents how the unchanged numbers, without profile assigned, would look in the sRGB space. The yellower image shows how the adjusted numbers look in sRGB. Does that sound right?

Quote
I can use manual levels in postprocessing, but I am unable to determine how to display the actual data numbers in the raw file. Personally, I prefer DCRaw for this purpose. Have you tried it?

I recently did a Google search on DCRaw and even downloaded something. But I couldn't get the program to work and decided it was beyond my expertise and/or probably not worth the hassle of trying to figure it out. I prefer programs with a user-friendly interface .
Title: Today's DSLR should have another exposure mode
Post by: Dennis on May 26, 2006, 07:46:10 am: Quote
Personally, I prefer DCRaw for this purpose. Have you tried it?
Could you tell us your option settings for linear conversion?

I am experimetning with

-v -3 -r 1 1 1 1

The problem with this set is, that it's still scaled, you can't tell for sure, if a channel is blown or not. Should I include

-o 0

to prevent converting it into sRGB, and thus leave the RGB values as they are? Could be a good idea.
Title: Today's DSLR should have another exposure mode
Post by: bjanes on May 26, 2006, 10:59:39 am: Quote
But what about the centre of the sun? That white spot is bigger than a mere specral highlight. Whatever the setting in ACR, it's 255,255,255, even with -4EC, which is okay by me. I'd expect the centre of the sun to be a blown highlight, but I was curious as to what a linear conversion would reveal and was very surprised to find that even that centre white spot does not seem to be blown. It's just a neutral white. The image appears to be actually underexposed by about 1/4 of a stop. That's close enough for me .

[attachment=601:attachment]
[a href=\"index.php?act=findpost&pid=66459\"][{POST_SNAPBACK}][/a]

Just because the conversion is linear, that does not mean it has not been scaled. The raw file is 0..4095, and the converted linear file should be is 0..255. To convert from the 12 bit raw to 8 bit linear output, the raw pixel value is divided by 16 (a 4 bit right shift in integer math).

I find it difficult to believe that values of 255 in ACR with -4EC do not represent blown channels. Since the linear outupt is around 214, I think it is likely that the divisor is closer to 19 than 16. Since the image is white balanced, we know that multipliers are involved and some scaling has been performed. An analagous situation would be to use the output sliders in Photoshop so that maximum output would be at 214 rather than 255--clipping now occurs at 214 instead of 255.

The easiest way to investigate this possibility is to perform a series of bracketed overexposures and see what the maximum value in the channels is when clipping occurs.

At base ISO most digital cameras set the gain so that sensor saturation results in a data number near full scale in the analog to digital converter. For example, with my Nikon D200, sensor saturation results in RGB values of 254, 249 and 253 expressed as 8 bits and 4064, 3984, and 4048 in 12 bits as determined by conversion with DCRaw with demosaicing and conversion to an RGB image. In this case, clipping occurs in the sensor. Full scale of 4095 is not reached at base ISO, but AD overflow with a maximum data numberof 4095 would occur at higher ISOs and the clipping would be in the AD converter at 4095.
Title: Today's DSLR should have another exposure mode
Post by: bjanes on May 26, 2006, 11:11:45 am: Quote
Could you tell us your option settings for linear conversion?

I am experimetning with

-v -3 -r 1 1 1 1

The problem with this set is, that it's still scaled, you can't tell for sure, if a channel is blown or not. Should I include

-o 0

to prevent converting it into sRGB, and thus leave the RGB values as they are? Could be a good idea.
[a href=\"index.php?act=findpost&pid=66621\"][{POST_SNAPBACK}][/a]

The latest version of CDRaw has a -D switch, which causes totally raw output with no scaling. There is no demosaicing and the output is gray scale 0..4095. If you want RGB output, the above switches with -o 0 should do the trick. The output is scaled by a factor of 16 to convert from 0..4095 (12 bit) to 0..65535 for display at 16 bits. The 12 bit output is very dark in Photoshop 15+1 display (0..32768).
Title: Today's DSLR should have another exposure mode
Post by: Ray on May 26, 2006, 11:30:02 am: Quote
I find it difficult to believe that values of 255 in ACR with -4EC do not represent blown channels.

Bill,
I'm not qualified to comment, except to say one might argue equally that, 'I find it difficult to believe that BB's default linear conversion is not accurate'.

I simply don't know. I'm mainly interested in practical results and this sunrise seems to be closely enough exposed to the right for me. Fortunately (or unfortunately depending on perspective), the foreground in the shadows is uninteresting, drought scorched grass. There's no need to bring out the shadows in this shot.
Title: Today's DSLR should have another exposure mode
Post by: jani on May 26, 2006, 12:23:57 pm: Quote
Well - reread the article. Pay extra attention to the rationale for the technique. It's about bits dedicated to the image data.
And what has "bits dedicated to the image data" got do do with detail?

It only affects detail to the extent that detail is affected by exposure.

I think we have a terminology problem here, and that we're not communicating quite well, but I'm obviously not in possession of the necessary vocabulary to improve on the situation.
Title: Today's DSLR should have another exposure mode
Post by: Dennis on May 26, 2006, 12:47:11 pm: Quote
The latest version of CDRaw has a -D switch, which causes totally raw output with no scaling. There is no demosaicing and the output is gray scale 0..4095. If you want RGB output, the above switches with -o 0 should do the trick.
Bill,

thanks for your explanations. Meanwhile, I did some testing an reading of your postings in the Adobe Forum. You say, you use the following options:

-m -n

So, in one case, we agree, since -m is equal to -o 0. See here (http://www.pochtar.com/jb/dcraw.man.htm), and testing prooves this true.

But in the other case, I think your conversion is faulty. The one reason is obvious:

-n is equal to -H 1, which means, that clipped channels are filled with shades of pink, which is not usefull when evaluating highlights. As long as you have no clipped channels in you selection - no problemo. But I don't like that.

For the other reason, I have to go further into detail. It's all about the multipliers. If you set the option -v, you'll see a line like this during conversion:
Scaling with black=0, pre_mul[] = 2.270731 1.000000 1.273082 1.000000
In lack of a documentation from Dave Coffin, I interpret those values as the multipliers of the direct values to the sensor data, seen as a square crop containing four pixels:

R G B G

My emphasis is on direct, so if you are out for the unbiased sensor data, you'll have to use the option set

-r 1 1 1 1

If you use the -i option, some data of the image file is listed. At the bottom, there are two interesting lines:
Daylight multipliers: 2.094750 0.922500 1.174418
Camera multipliers: 271.000000 256.000000 751.000000 256.000000
These are the values from a Raw file of a Konica Minolta A2.

The first line defines the multipliers for the R G B values, which are supposed to balance the colors with daylight. dcraw sets the smallest value to 1 and adjusts the other colors. This multiplier set is used, if you convert without any (relevant) options set. The computed multipliers displayed are the above mentioned:

0.922500 scaled to 1.000000 (G)
2.094750 : 0.922500 = 2.270731 for R and
1.174418 : 0.922500 = 1.273082 for B

In the second line, you find the values for R G B G according to the set WB. It's the same scheme as above:

256.000000 scaled to 1.000000
271 : 256 = 1.058594
751 : 256 = 2.933594 (pretty extreme value, AWB at tungsten)

Exactly those values, you'll see if using the -w option (Use the color balance specified by the camera).

No, you are using the -n option, which gives the following multipliers:
1.000000 0.440387 0.560648 0.440387
This is a remarkable notation, since usually, the smallest value is set to 1.000000. So even if you type an option like this:

-r 0.5 1 1 1

it's converted to this form:
1.000000 2.000000 2.000000 2.000000
If you set the smallest multiplier (0.440387) to 1, you'll see that the ratio is the same as with the daylight multipliers (edited). But now he sets the channel with the highest multiplier to one.

Anyway, you see, that using the -n option leads to false R G B values in the image, in the meaning of not as they were recorded. If you want all channels exactly as they were recorded by the sensor, you'll have to use the

-r 1 1 1 1

option, which BTW overrides the -n option.

Quote
The output is scaled by a factor of 16 to convert from 0..4095 (12 bit) to 0..65535 for display at 16 bits. The 12 bit output is very dark in Photoshop 15+1 display (0..32768).
Oh, yes, thanks for this hint. I was confused, since the values shifted considerably due to the sRGB conversion. The -o 0 or -m otpion solved the problem.

To sum it up, I recommend the following set for linear unbiased conversion:

dcraw.exe -3 -m -r 1 1 1 1 {file name}

Any comments?
Title: Today's DSLR should have another exposure mode
Post by: John Sheehy on May 26, 2006, 02:40:24 pm: Quote
Well - reread the article. Pay extra attention to the rationale for the technique. It's about bits dedicated to the image data.

That may be what the article emphasizes, but there is more to it than that. The signal-to-noise ratio is higher in the upper RAW ranges of a given ISO, including the distracting banding noise that some cameras exhibit in under-exposures.

Quote
It's an overexposure technique geared towards heavy post-processing that benefits from extra bits dedicated to image information, not a guide to correct exposure.

Actually, there really shouldn't be that much post-prcoessing to handle a high RAW exposure. At least in theory, the exposure slider in a converter merely needs to be moved to the left (not all of them work like this, though). What requires lots of post-processing sometimes is a "normal" exposure (swhat the camera's metering thinks is normal), and trying topreserve the RAW highlights without darkening the image.
Title: Today's DSLR should have another exposure mode
Post by: John Sheehy on May 26, 2006, 02:46:50 pm: Quote
Oh. Then it's not blown Sorry for my remark.

I obviously assumed that "white" meant all 255s.
[a href=\"index.php?act=findpost&pid=66594\"][{POST_SNAPBACK}][/a]

All 214/214/214 over an area does indicate clipping; something was clipped somewhere in the process, and then darkened in the final output.
Title: Today's DSLR should have another exposure mode
Post by: John Sheehy on May 26, 2006, 06:06:02 pm: Quote
At base ISO most digital cameras set the gain so that sensor saturation results in a data number near full scale in the analog to digital converter. For example, with my Nikon D200, sensor saturation results in RGB values of 254, 249 and 253 expressed as 8 bits and 4064, 3984, and 4048 in 12 bits as determined by conversion with DCRaw with demosaicing and conversion to an RGB image. In this case, clipping occurs in the sensor. Full scale of 4095 is not reached at base ISO, but AD overflow with a maximum data numberof 4095 would occur at higher ISOs and the clipping would be in the AD converter at 4095.
[a href=\"index.php?act=findpost&pid=66634\"][{POST_SNAPBACK}][/a]

It is still possible that there is another reason for that. Many DLSRs clip at less than 4095 for various reasons. Canon 1DmkII cameras slip in the low 3700s, depending on the ISO; 5D cameras clip at 3962 at every ISO, etc. I've looked at samples of clipped D200 NEFs that had 4095 at ISO 100 in some verticle lines, but a max of 4024 or thereabouts in alternating lines. The Canon 10D clips lower at ISO 100 and increases slightly up to 800, etc.
Title: Today's DSLR should have another exposure mode
Post by: bjanes on May 26, 2006, 06:20:57 pm: see following post
Title: Today's DSLR should have another exposure mode
Post by: bjanes on May 26, 2006, 06:26:18 pm: Quote
Bill,

To sum it up, I recommend the following set for linear unbiased conversion:

dcraw.exe -3 -m -r 1 1 1 1 {file name}

Any comments?
[a href=\"index.php?act=findpost&pid=66644\"][{POST_SNAPBACK}][/a]

Dennis,

Yes, I think those switches are fine for our purpose, but personally I use the -H 1 option (same as -n), since I do not want any clipping. It seems to me, if you want to evaluate the status of the raw file, you do not want any clippping. The default is -H 0.

In testing with a heavily overexposed Macbeth CC, I saw little, if any, difference between -H 1 and -H 0 switches when using multipliers of 1 and raw output (-o 0). The clipped high lights did not fill with pink with the -H 1 option. I superimposed the two conversions in Photoshop and used the difference blending option, and the screen was totally black--no visible difference. Here is the -H 1 conversion converted to 8 bits and downsized. As you can see, the left two neutral patches of the color checker are blown to white.

[attachment=619:attachment]

I then converted the same files but to sRGB (-o 1) and "as shot" white balance (-w) with and without the highlight clipping (-H 0 and -H 1). Here there is a big difference. Also, the multipliers are different. I think the attachments are self explanatory.

-H 0 -w -o 1

[attachment=621:attachment]

-H 1 -w -o 1

[attachment=620:attachment]

[attachment=625:attachment]
Title: Today's DSLR should have another exposure mode
Post by: bjanes on May 26, 2006, 06:31:34 pm: Quote
All 214/214/214 over an area does indicate clipping; something was clipped somewhere in the process, and then darkened in the final output.
[a href=\"index.php?act=findpost&pid=66651\"][{POST_SNAPBACK}][/a]

Exactly what I said in an earlier post. The sun's disc would most likely have been red in the actual scene and it has been clipped to white. I'm glad someone agrees with me.
Title: Today's DSLR should have another exposure mode
Post by: Dennis on May 26, 2006, 09:07:36 pm: Quote
Yes, I think those switches are fine for our purpose, but personally I use the -H 1 option (same as -n), since I do not want any clipping.
But if you have some clipping, your color values in the histogram are corrupt due to pink tinting introduced with the -n or -H option activated.

Quote
In testing with a heavily overexposed Macbeth CC, I saw little, if any, difference between -H 1 and -H 0 switches when using multipliers of 1 and raw output (-o 0)
There is no difference, since any -r setting overwrites any -a, -w or -H (and thus -n) settings. That's what I tried to explain: With -a, -w and -H dcraw set the multipliers to a certain value. But if you set the -r option, those switches are useless, since the -r option now sets the multipliers. So any set like

-n -r 1 1 1 1

or

-H 0 -r 1 1 1 1

or

-w -r 1 1 1 1

are redundand, since -r is stronger than the others.

Quote
I then converted the same files but to sRGB (-o 1) and "as shot" white balance (-w) with and without the highlight clipping (-H 0 and -H 1). Here there is a big difference. Also, the multipliers are different. I think the attachments are self explanatory.
Here, something is obviously wrong. Your cmd screenshot shows, that you processed two different images, not the same with different settings. Again please check the issue with the -r switch in combination with -w or -H.
Title: Today's DSLR should have another exposure mode
Post by: bjanes on May 26, 2006, 10:32:38 pm: Quote
But if you have some clipping, your color values in the histogram are corrupt due to pink tinting introduced with the -n or -H option activated.

There is no difference, since any -r setting overwrites any -a, -w or -H (and thus -n) settings. That's what I tried to explain: With -a, -w and -H dcraw set the multipliers to a certain value. But if you set the -r option, those switches are useless, since the -r option now sets the multipliers. So any set like

-n -r 1 1 1 1

or

-H 0 -r 1 1 1 1

or

-w -r 1 1 1 1

are redundand, since -r is stronger than the others.

[a href=\"index.php?act=findpost&pid=66677\"][{POST_SNAPBACK}][/a]

I think you are correct here. However, some of the command line switches have changed recently between the version I was previously using (v 8.05) and the most recent one (v 8.18, May 18, 2006). This led to some confusion on my part.

In the previous version, -m -n -3 caused the file to be converted as raw without white balance and it was not necessary to use the -r 1 1 1 1. In fact, the -r switch previously set the red multiplier only.

In the current version, it is necessary to use the -r 1 1 1 1 switch for raw output without white balance, and -m is no longer sufficient by itself. As you have pointed out, the -n switch is overridden, and I don't see why you previously disagreed with its use in this situation; it is simply ignored. I have compiled the previous version as DCRaw.exe and the current as DCRawb.exe. Here are the verbose reports with the same switches and the same file being processed. As you can see, the results are quite different. At least, the old version showed the multipliers as 16 (for 16 bit output) and not 1 (for 12 bit). A bit confusing. I have not yet figured out a way to get 12 bit output with the -3 switch. Setting the -b to 0.0625 does not work, and one must divide the 15+1 Photoshop values by 8 to obtain the raw data number.

[attachment=626:attachment]

If you look at the valid switches as shown by typing DCRaw without a filename, the -m and -n switches are no longer shown as valid, but they are still processed. At least their meaning has not changed, in contrast to the -r switch.

[attachment=627:attachment]

Quote
Here, something is obviously wrong. Your cmd screenshot shows, that you processed two different images, not the same with different settings. Again please check the issue with the -r switch in combination with -w or -H.
[a href=\"index.php?act=findpost&pid=66677\"][{POST_SNAPBACK}][/a]

I inadvertently uploaded the wrong screen capture, but the same image was indeed processed with the shown results. My post has been edited to show the corrected screen capture. I agree the -w and -H are meaningless with the -r switch.
Title: Today's DSLR should have another exposure mode
Post by: Serge Cashman on May 27, 2006, 01:54:51 am: <edit> Post deleted by author.
Title: Today's DSLR should have another exposure mode
Post by: gochugogi on May 27, 2006, 11:10:53 pm: Cool, I envision a new pic mode "ER" placed on the Command Dial between Sports and Landscape modes of the EOS 30D MK II. It will be buried in the menus for Rebel and 1-series bodies.
Title: Today's DSLR should have another exposure mode
Post by: Ray on May 31, 2006, 05:13:19 am: Quote
All 214/214/214 over an area does indicate clipping; something was clipped somewhere in the process, and then darkened in the final output.
[a href=\"index.php?act=findpost&pid=66651\"][{POST_SNAPBACK}][/a]

Agreed, unless one happens to have an extremely neutral patch of gray in the image. It's unlikely the centre of the sun is going to be anything less than white, yellow or red, as in the following image of a setting sun which doesn't appear to be clipped.

[attachment=641:attachment]

Having experimented with a few conversions using BB's linear mode, I can see no advantage whatsoever in linear conversion. ACR and RSP seem to do at least an equal job of retaining highlight detail, if not slightly better, and without the hassle of devising and applying an appropriate tone curve.

Consider the following shot of a crocodile's response to a tasty pork chop. Detail at the back of the crocodile's mouth is moderately blown. With a straight conversion, the effect is as though the croc has swallowed a dozen light bulbs that are still working.

Using ACR and dual conversion (one at -4 EC) I think I've managed to tame the glow.

[attachment=642:attachment]

However, I was curious as to how ACR, RSP and BB's linear mode would handle these partially blown highlights. RSP actually seems to produce the most pleasing result. ACR seems to produce patches of almost neutral grey, perhaps due to greater contrast. BB's linear conversion seems to recover less highlight detail in general. (A word of warning: those of a nervous disposition should not click on 'enlarge').

[attachment=643:attachment]

Dave Coffin, the author of DCraw, seems to think that ACR attempts to reconstruct lost highlight detail. That's the impression I also get if I assume that BB's linear conversion mode is providing the true picture.

I'd be interested to learn from those who are using DCraw if they think it can provide greater recovery of highlight detail than commonly used converters like ACR or RSP.

A footnote: I neglected to turn off RSP's 'detail extractor', which is part of the reason the RSP conversion looks better.

All D60 images, BTW.
Title: Today's DSLR should have another exposure mode
Post by: bjanes on May 31, 2006, 09:36:20 am: Quote
Having experimented with a few conversions using BB's linear mode, I can see no advantage whatsoever in linear conversion. ACR and RSP seem to do at least an equal job of retaining highlight detail, if not slightly better, and without the hassle of devising and applying an appropriate tone curve.

However, I was curious as to how ACR, RSP and BB's linear mode would handle these partially blown highlights. RSP actually seems to produce the most pleasing result. ACR seems to produce patches of almost neutral grey, perhaps due to greater contrast. BB's linear conversion seems to recover less highlight detail in general. (A word of warning: those of a nervous disposition should not click on 'enlarge').

Dave Coffin, the author of DCraw, seems to think that ACR attempts to reconstruct lost highlight detail. That's the impression I also get if I assume that BB's linear conversion mode is providing the true picture.

All D60 images, BTW.
[a href=\"index.php?act=findpost&pid=66985\"][{POST_SNAPBACK}][/a]

Linear mapping of the tone values will not improve highlight detail, but will merely remap the lower tone values. Here are some Imitest produced characteristic curves for the Nikon D200 in linear space converted with DCRaw and in gamma 2.2 with Nikon Capture and Adobe Camera Raw (both with default normal tone curves). Also shown is literal encoding for gamma 2.2 and 1.8.

The highlight values are similar, but the three quarter tones in the gamma 2.2 spaces are considerably brighter, as expected. In the quarter tones both ACR and NC roll off the shadow response.

[attachment=644:attachment]

With the D200 and Adobe Camera Raw, when the highlights are set just below 255 in ACR, the raw data number is about 3550 in my tests, not 4095 as one might expect. This is consistent with what John Sheehy has also posted. Since the highlights are placed at 3550 in the raw file, there is some headroom.

As for highlight recovery, I am posting some observations for comment. Here are Stouffer stepwedge exposures in 0.33 EV increments. The linear raw conversion without white balance (DCRaw) is on the left and the ACR conversion with default settings is on the right. Stof 03 Step 1 gives an ACR reading of 251 and Stof 05 and Stof 06 (with +EV 0.66 and +EV 1 exposure) are blown in ACR with a normal exposure setting. In the DCRaw conversion, Stof 06 is beginning to blow in the green channel, as indicated by the color shift toward white.

[attachment=645:attachment]

With Stof 05, highlight recovery in ACR is possible with a -0.66 EV correction as shown in this screen capture (posted as a GIF to show good text; please ignore the posterization):

[attachment=646:attachment]

With Sfof 06, it is not possible to set the highlights to less than 255 even with -4 EV correction and shadow tones are lost:

[attachment=647:attachment]

Because of the headroom in the raw file, highlight recovery is straight forward with slight "overexposure", since the raw channels are not blown. However, when the green channel starts to blow, highlight recovery is less successful. If one had used a magenta filter to balance the channels, I am not sure that highlight recovery would work very well.
Title: Today's DSLR should have another exposure mode
Post by: Dennis on May 31, 2006, 01:03:49 pm: Quote
However, I was curious as to how ACR, RSP and BB's linear mode would handle these partially blown highlights. RSP actually seems to produce the most pleasing result. ACR seems to produce patches of almost neutral grey, perhaps due to greater contrast.
I see something different. RSP is rendering the clipped colors to grey. ACR is trying to keep a color and tints some areas in a fleshy pink tone, which are neutral in the RSP picture. Then there's a sudden jump to neutral grey patches in some small spots, where apparently the clipping reached a level, which didn't allow ACR to reconstruct any color. This is a known behavior of ACR. But AFAIK it does a better job in reconstructing highlights than any other raw converter.

Quote
Dave Coffin, the author of DCraw, seems to think that ACR attempts to reconstruct lost highlight detail.
And this is obviously the case. I just tested out the limits of my Minolta A2 und compared ACR and dcraw's highlight recovery abilities extensivly. My target was the white wall of a house, lit by cloudy sky. I bracketed in 1/3 f stops from +1.7 EV up to +4.0 EV. First, I zoomed to the wall to get an white only frame for using dcraw's capability of analysing a picture and setting the right multipliers (option -a). Using these multipliers, I converted the bracketed shots. The last one with good highlight detail was the +2.7 EV exposure. The next exposure (+3.0 EV) suffered completely blown sections of the white wall. A linear conversion (-r 1 1 1 1 -m) showed the problem: While the red and blue channel contained good details, the green channel was completely blown. I was not able to produce any acceptable conversion - even not using the -H [2..9] option, which is supposed to reconstruct the highlights. All it did, was to introduce a massive pink cast. Looking at the channels, it turned out, that the green channel was simply filled with a way too dark shade of grey (R had an average of 168, B of 117 and G was filled with plain 109). So, what should be white wall with fine detail (rough plaster) got a dirty pink wall with greenish shadows.

ACR does a way, way better job recovering highlights: The channels of the same +3.0 EV overexposed shot were evenly filled with equal shades of grey, containing all detail. Since we know from the above linear conversion, that the green channel is absolutely blown, ACR reconstructs the green channel with detail from the two others, and balances the result that way, that i's a neutral grey. This way, ACR is able to reconstruct even the highlight's in a +3.3 EV overexposed shot. Even the +3.7 EV exposure is ACR able to handle pretty well, not blowing out all the white wall, but leaving some detail. Only the +4.0 EV image is as bad, as the +3.0 EV was with dcraw.

So, recovering highlights, ACR wins hands down. It is possible, to get all information out of the Raw file with dcraw using a linear conversion, but the image has a strong color cast then, and I wasn't able to balance the colors.

In terms of resolving of fine detail, dcraw wins by a small margin. If you have some very very fine detail in the picture, as you find it with fabrics, dcraw has an edge, a small one.
Title: Today's DSLR should have another exposure mode
Post by: Dennis on May 31, 2006, 01:44:51 pm: Here I add a sample:
The first row shows the image converted linear with dcraw, the second row converted with highlight recovery of dcraw and the third row the conversion done with ACR. This is a crop of the white wall, exposed at +3.0 EV. One clearly can see, that the green channel is completely blown, and how dcraw and ACR do different things to reconstruct the highlights.
Title: Today's DSLR should have another exposure mode
Post by: Ray on June 02, 2006, 01:10:52 am: Quote
So, recovering highlights, ACR wins hands down. It is possible, to get all information out of the Raw file with dcraw using a linear conversion, but the image has a strong color cast then, and I wasn't able to balance the colors.

In terms of resolving of fine detail, dcraw wins by a small margin. If you have some very very fine detail in the picture, as you find it with fabrics, dcraw has an edge, a small one.
[a href=\"index.php?act=findpost&pid=67023\"][{POST_SNAPBACK}][/a]

Thanks, bjanes and Dennis for your response. I tend to agree with Dennis that ACR is (some how) able to extract or reconstruct more color detail in blown highlights. I'm not sure if Capture One is able to better these results, but ACR's reconstruction is mostly credible, although the cyan shift in a blown blue sky could be better. (Or maybe not. What do I know!)

I was recently looking at some rain forest shots with sunlight streaming through. This is a very high DR situation. Tree trunks with direct sunlight are likely to be blown, or the shadows are likely to be very noisy, depending on choice of shutter speed.

In terms of detail from the luminous perspective, there's little difference between RSP and ACR. Howver, with a 'daylight' WB, the ACR conversion brings out the green of the moss on the trunk, which I know was there. I've failed to get RSP to produce that credible green.

Sorry, I'm on my 64 system and wouldn't attempt to post images demonstrating this.

Oops! Forgot to address the second part of the quote. How does DCRaw compare with RSP redarding fine detail extraction?

My impression is, that RSP produces more detail than ACR.
Title: Today's DSLR should have another exposure mode
Post by: bjanes on June 02, 2006, 11:10:35 am: Quote
Thanks, bjanes and Dennis for your response. I tend to agree with Dennis that ACR is (some how) able to extract or reconstruct more color detail in blown highlights. I'm not sure if Capture One is able to better these results, but ACR's reconstruction is mostly credible, although the cyan shift in a blown blue sky could be better. (Or maybe not. What do I know!)

I was recently looking at some rain forest shots with sunlight streaming through. This is a very high DR situation. Tree trunks with direct sunlight are likely to be blown, or the shadows are likely to be very noisy, depending on choice of shutter speed.

In terms of detail from the luminous perspective, there's little difference between RSP and ACR. Howver, with a 'daylight' WB, the ACR conversion brings out the green of the moss on the trunk, which I know was there. I've failed to get RSP to produce that credible green.

My impression is, that RSP produces more detail than ACR.
[{POST_SNAPBACK}][/a] (http://index.php?act=findpost&pid=67153\")

When dealing with very high DR situations, one should not overlook the possibility of doing a double conversion, one for highlights and another for shadows, and then blending them digitally. Jeff Schewe describes this process in a white paper on the Adobe web site (he has reportedly submitted an updated version, but it is not yet posted) and Steve Bingham also describes a slightly different method.

[a href=\"http://www.adobe.com/digitalimag/pdfs/highlight_recovery.pdf]http://www.adobe.com/digitalimag/pdfs/highlight_recovery.pdf[/url]

http://dustylens.com/luminosity_mask.htm (http://dustylens.com/luminosity_mask.htm)

If the situation is static and several exposures from a tripod mounted camera are possible, then HDR in Photoshop is an even better option.
Title: Today's DSLR should have another exposure mode
Post by: Ray on June 03, 2006, 11:53:21 am: Quote
When dealing with very high DR situations, one should not overlook the possibility of doing a double conversion

Bill,
I use this technique quite often but not to recover highlight detail, which one can do with a single conversion and a negative EC, but to reduce noise and improve image quality in the shadows. For example, I'll often blend 2 conversions, one of which has a -2EC setting and the other a +2EC. However, the improvements are fairly marginal and this technique is no substitute for 2 separate exposures.

I'd like to find a good algorithm that automatically aligns images which are slightly out of register, which always happens when attempting to blend two handheld shots. I'm surprised that Photoshop's HDR attempt at aligning images is so poor. I can always do a better job manually, although I have some trouble with precise rotation of the top layer.

I would expect that the 1D MK2 with its fast frame rate would be a better tool than the 5D for providing good shots for blending. With the 5D, whatever the exposure, I'm not able to take 2 shots within a shorter period than about 2/3rds of a sec, which is a long time for things to get out of register, whether it's due to movement of the subject or camera shake.

As you've gathered, I don't like carrying a tripod around.
Title: Today's DSLR should have another exposure mode
Post by: John Sheehy on June 03, 2006, 12:38:26 pm: Quote
Bill,
I use this technique quite often but not to recover highlight detail, which one can do with a single conversion and a negative EC, but to reduce noise and improve image quality in the shadows. For example, I'll often blend 2 conversions, one of which has a -2EC setting and the other a +2EC. However, the improvements are fairly marginal and this technique is no substitute for 2 separate exposures.
[a href=\"index.php?act=findpost&pid=67279\"][{POST_SNAPBACK}][/a]

I've always felt that the fact that people need to do this, to get results, is only a reflection on the primitive state of RAW converters or the post-processing software. There is absolutely no reason why a 16-bit TIFF can't carry all the DR of the RAW file. The amount of shadow DR potential in a 16-bit TIFF gamma-adjusted is astronomical, compared to what is in a RAW file, and a linear 16-bit TIFF (a full conversion but without tone re-mapping) is sufficient.

Post-processing could do any kind of s-curve or zone-based contrast boosts/enhancements.

Blending is awkward, and full of artifacts, and really should only be necessary for multiple shutter events. Even with multiple shutter events, the HDR process should be done to the data in a totally linear state. I don't know why PS CS2 doesn't merge the data in a RAW state, at a higher bit depth, and then convert it. That would make so much more sense, as the linear data is mathematically simple. If you shoot a grey step card at 1/100, and then again at the same ISO and aperture at 1/1000, the ratio of the average level of each square, minus the blackpoint for that image, is *EXACTLY* the same ratio between the two images in the RAW data. The only thing that differs, other than the scaling difference between the two images, is the S/N ratio. There are minor exceptions, of course; the Canon 20D, for instance, is not linear at ISO 100 in the top half stop or so of RAW highlights, due to some kind of data manipulation (the opposite of what you'd expect from saturation).
Title: Today's DSLR should have another exposure mode
Post by: Ray on June 03, 2006, 01:26:20 pm: Quote
I've always felt that the fact that people need to do this, to get results, is only a reflection on the primitive state of RAW converters or the post-processing software. There is absolutely no reason why a 16-bit TIFF can't carry all the DR of the RAW file. The amount of shadow DR potential in a 16-bit TIFF gamma-adjusted is astronomical, compared to what is in a RAW file, and a linear 16-bit TIFF (a full conversion but without tone re-mapping) is sufficient.

John,
That might be true. There is more than one way to skin a cat. I imagine that anyone more skilled in PS than I am could do an equal or better job with a single conversion into 16 bit tif than I can do with a dual conversion.

I use the layer mask method described in an LL tutorial here (http://www.luminous-landscape.com/tutorials/digital-blending.shtml) . I adjust the levels of the individual layers before flattening and find the whole process very quick and easy. The only problem is a tendency to getting halos if the EC gap is too extreme between the 2 conversions. But this problem can usually be fixed with the gamma slider in levels with one or both of the layers and/or a greater degree of Gausiian blurring of the B&W mask. If not, then the whole process has to be repeated with less extreme differences in EC.

I've always assumed that a +2EC (for example) conversion will provide more bits for the shadows and provide better quantization, which in turn translates to better tonality in the shadows and marginally better S/N.
Title: Today's DSLR should have another exposure mode
Post by: Dennis on June 04, 2006, 12:50:20 pm: Quote
I've always felt that the fact that people need to do this, to get results, is only a reflection on the primitive state of RAW converters or the post-processing software. There is absolutely no reason why a 16-bit TIFF can't carry all the DR of the RAW file.
You're right, but a 16bit TIFF is much bigger than a Raw file. Further, you have already interpolated RGB triples in a TIFF, so the real deal is still the raw format. It's the smallest file, containing the most information.
Title: Today's DSLR should have another exposure mode
Post by: Dennis on June 04, 2006, 12:51:44 pm: Quote
When dealing with very high DR situations, one should not overlook the possibility of doing a double conversion, one for highlights and another for shadows, and then blending them digitally.
Yes, if the raw converter is able to produce a good highlight conversion.
Title: Today's DSLR should have another exposure mode
Post by: Ray on June 04, 2006, 09:41:45 pm: Quote
Yes, if the raw converter is able to produce a good highlight conversion.
[a href=\"index.php?act=findpost&pid=67371\"][{POST_SNAPBACK}][/a]

I don't see the dual conversion method relating directly to recovering highlights. Recovering highlights is dependent upon the converter, as you mention. ACR and C1 appear to be best in this regard. The problem is, after applying the negative EC to recover highlights (-2 EC or whatever), it's then difficult to recover the vibrancy and general tonality of the lower mid-tones and shadows from the converted TIF, even if it's in 16 bit.

Dual conversion is the best technique I happen to know which can improve the tonality of the darker parts of an image with recovered highlights.
Title: Today's DSLR should have another exposure mode
Post by: Dennis on June 05, 2006, 06:44:25 am: Quote
I don't see the dual conversion method relating directly to recovering highlights.
For the dual conversion method, you need one conversion with good highlights, right? See my picture above. With dcraw, there's not much in the highlights worth a dual conversion.
Title: Today's DSLR should have another exposure mode
Post by: Ray on June 05, 2006, 09:05:42 am: Quote
For the dual conversion method, you need one conversion with good highlights, right? [a href=\"index.php?act=findpost&pid=67420\"][{POST_SNAPBACK}][/a]

I need one conversion with good highlights, period. If I think the shadows are slightly degraded as a consequence of a negative EC applied to a wide DR subject, I might think it worthwhile to blend the image with a second conversion which brings out the shadows and improves tonality.
Title: Today's DSLR should have another exposure mode
Post by: PeterLange on June 05, 2006, 04:40:12 pm: Quote
.... The problem is, after applying the negative EC to recover highlights (-2 EC or whatever), it's then difficult to recover the vibrancy and general tonality of the lower mid-tones and shadows from the converted TIF, even if it's in 16 bit.

Dual conversion is the best technique I happen to know which can improve the tonality of the darker parts of an image with recovered highlights.

Coincidently, I’ve been gone through some respective tests this weekend.

First, a ‘virgin conversion’ was accomplished by setting Brightness & Contrast to zero (curve tab linear). Thus, blocking any tone curve (as far as I can tell). Everything referring to ACR, ProPhoto RGB @ 16 bit. Exposure was set to max possible without clipping textured highlights.

Then in Photoshop, a Curves’ adjust layer (i.e. an all-brightening sigmoidal curve) + Contrast mask were applied.

Now after comparing with diverse techniques which require blending of multi-Raw-conversions (+/- EC), I don’t see a competitive edge with these procedures.

So it seems that all ‘bit information’ silently lies in said ‘virgin conversion’, which can look quite dark at first. Things just have to be pulled-out, while preventing any damage ofthe highlights.

Peter

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Title: Today's DSLR should have another exposure mode
Post by: Ray on June 06, 2006, 12:21:48 am: Quote
So it seems that all ‘bit information’ silently lies in said ‘virgin conversion’, which can look quite dark at first. Things just have to be pulled-out, while preventing any damage ofthe highlights.
[a href=\"index.php?act=findpost&pid=67474\"][{POST_SNAPBACK}][/a]

Peter,
I think you are probably right. As I wrote before, there's more than one way to skin a cat. Photoshop is a complex program and one can achieve a similar end result through different processes.

Whenever I sit down at my computer to process some images, I have a choice of spending the time learning about Photoshop, or processing my images. I have that choice because I'm an amateur, but I generally prefer to spend the time processing my images with the few trusted techniques I'm familiar with.

I see dual conversion as one such technique of achieving a particular, desired end result. The technique seems to be beneficial with some images, but not with others, and it may well not have any advantage at all for someone more aware of the processing options Photoshop has to offer.

Geez! Posting on this site is certainly an exercise in humility .
Title: Today's DSLR should have another exposure mode
Post by: Dennis on June 06, 2006, 07:40:03 am: Quote
I need one conversion with good highlights
That's, what I am saying. The quality of the highlights depends on the raw conversion software, period.

Quote
Everything referring to ACR, ProPhoto RGB @ 16 bit.
...
So it seems that all ‘bit information’ silently lies in said ‘virgin conversion’, which can look quite dark at first.
Of course, that's true. There's is no loss in tonalities converting a 12 bit raw into a linear 16 bit .psd file, especially, if you do not convert the gamut. If this is the goal, dcraw is your tool.
Title: Today's DSLR should have another exposure mode
Post by: PeterLange on June 06, 2006, 03:03:55 pm: Quote
Whenever I sit down at my computer to process some images, I have a choice of spending the time learning about Photoshop, or processing my images. I have that choice because I'm an amateur, but I generally prefer to spend the time processing my images with the few trusted techniques I'm familiar with.

OK.

Cheers! Peter

--
Title: Today's DSLR should have another exposure mode
Post by: jani on June 07, 2006, 05:45:55 am: Just FYI, Lightroom appears to do a much better job at this than the default ACR interface.

I've played a bit around with it to extract shadow details and pull down highlights from a family shoot last weekend, and it seems to be working very well.

I only wish that the 20D's metering system wouldn't overexpose so often (maybe I need to get the meter cleaned up ...).
Title: Today's DSLR should have another exposure mode
Post by: Ray on June 07, 2006, 06:47:16 am: Well, I can't let this be. I've been under the delusion all this time that doing a +EC conversion will provide more bits to describe whatever data is in the RAW image and consequently provide better tonality in the shadows.

I've just spent some time revisiting some conversions I did a while ago using the dual conversion method, which I thought was serving some useful purpose.

I now find that it was serving no purpose whatsoever. What's really surprising is that a -4EC conversion into 16 bit tif and ProPhoto RGB still seems to retain the full tonality of the RAW image. This leaves me a bit dumbfounded because the implication is, one could convert all images with a -4EC just to make sure one had retained all available highlight detail. There's no disadvantage except the additional time taken making curves adjustments.

The following images have had no sharpness, contrast or saturation adjustments outside of a simple RGB curves' adjustment or blending procedure. They are not finished, processed images. I'm just looking for any qualities that the blended image might have that can't be easily duplicated with curves applied to the very dark -4EC conversion. I can't find any. The slightly greater contrast noticeable in the small crop of the 'curves' adjusted' image can be changed either way. I just think the images are close enough to demonstrate the point and haven't bothered to get them more closely matched.

[attachment=663:attachment] [attachment=664:attachment]

[attachment=665:attachment] [attachment=666:attachment]

I don't why the curves preview image looks like that.
Title: Today's DSLR should have another exposure mode
Post by: John Sheehy on June 07, 2006, 11:27:17 am: Quote
I only wish that the 20D's metering system wouldn't overexpose so often (maybe I need to get the meter cleaned up ...).
[a href=\"index.php?act=findpost&pid=67600\"][{POST_SNAPBACK}][/a]

My 20D is usually set to +2/3 EC by default. The lowest I generally go is -2/3 for Great Egrets (bright white birds) small in the frame. For ultra-low-contrast scenes, I find that the 20D limit of +2 EC is insufficient. My 20D agrees with my Sekonic L-558 on a white wall.
Title: Today's DSLR should have another exposure mode
Post by: PeterLange on June 07, 2006, 02:51:18 pm: Quote
Well, I can't let this be. ...
Seems to be the same with me .

Ray,

IF I may add a proposal … with all humility; being well aware that the following schematic approach can’t be ideal for every scene / image:

/> In ACR, all tonal controls: Exposure, Shadows, Brightness and Contrast are initially set to 0 (- zero -; curve tab linear).

/> Alt/click on the Exposure slider, move it left or right, to find this sweet spot of maximum Exposure which does not produce any relevant additional clipping. I mean, some pixel of the sky seem to be already irrevocably clipped and obviously can’t be recovered. So the task is to find the max Exposure setting which does not *significantly* enlarge these areas.
Admittedly, this step is a little bit a matter of feeling and in general the main ‘rule’ is not to clip any textured highlights. Most typically this ends in a +/- 0.75EC range, but that's of course just a my 'single'-experience.

/> Set the Shadows slider somewhere reasonably towards the commencement of the histogram. Leave Brightness & Contrast at zero. Click OK to process the file from ACR to Photoshop (ProPhoto RGB, 16 bit).

The following three steps can be easily recorded as an Action:
/> Ctrl/click on the RGB composite channel to select everything visible
/> Ctrl + Shift + I to invert the selection
/> Add a Curves’ adjust layer (80% Opacity and Normal blend mode) which then will carry the inverted selection as a layer mask. The curve itself is a quite special one; it is defined by the following 6 anchor points for Input/Output = 31/40, 56/78, 83/124, 114/172, 147/212 and 180/240.

Then, manually operated again:
/> Alt/click on the layer mask
/> Apply an appropriate Theshold to cover & protect only the brightest regions by pure black, while the rest of the mask gets white.
/> Apply a crude Gaussian Blur of some pixel width (maybe 10 or so)
/> Change back to normal view to fine-tune Opacity

Frankly, I’m using this technique since some weeks, it’s simple in essence and I’m surprised how often it works without further effort (referring to respective ‘HDR’ cases which can’t be adequately treated by the ACR global controls only). So at the risk that it doesn’t work here and it’s finally me looking – I’d like to invite you to give it a try.

Peter

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Title: Today's DSLR should have another exposure mode
Post by: Ray on June 07, 2006, 09:46:57 pm: Quote
Seems to be the same with me .
Ray,

IF I may add a proposal … with all humility; being well aware that the following schematic approach can’t be ideal for every scene / image:
/> In ACR, all tonal controls: Exposure, Shadows, Brightness and Contrast are initially set to 0 (- zero -; curve tab linear).

/> Alt/click on the Exposure slider, move it left or right, to find this sweet spot of maximum Exposure which does not produce any relevant additional clipping. I mean, some pixel of the sky seem to be already irrevocably clipped and obviously can’t be recovered. So the task is to find the max Exposure setting which does not *significantly* enlarge these areas.
Admittedly, this step is a little bit a matter of feeling and in general the main ‘rule’ is not to clip any textured highlights. Most typically this ends in a +/- 0.75EC range, but that's of course just a my 'single'-experience.

/> Set the Shadows slider somewhere reasonably towards the commencement of the histogram. Leave Brightness & Contrast at zero. Click OK to process the file from ACR to Photoshop (ProPhoto RGB, 16 bit).

The following three steps can be easily recorded as an Action:
/> Ctrl/click on the RGB composite channel to select everything visible
/> Ctrl + Shift + I to invert the selection
/> Add a Curves’ adjust layer (80% Opacity and Normal blend mode) which then will carry the inverted selection as a layer mask. The curve itself is a quite special one; it is defined by the following 6 anchor points for Input/Output = 31/40, 56/78, 83/124, 114/172, 147/212 and 180/240.

Then, manually operated again:
/> Alt/click on the layer mask
/> Apply an appropriate Theshold to cover & protect only the brightest regions by pure black, while the rest of the mask gets white.
/> Apply a crude Gaussian Blur of some pixel width (maybe 10 or so)
/> Change back to normal view to fine-tune Opacity
Frankly, I’m using this technique since some weeks, it’s simple in essence and I’m surprised how often it works without further effort (referring to respective ‘HDR’ cases which can’t be adequately treated by the ACR global controls only). So at the risk that it doesn’t work here and it’s finally me looking – I’d like to invite you to give it a try.

Peter

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[a href=\"index.php?act=findpost&pid=67636\"][{POST_SNAPBACK}][/a]

Peter,
Thanks for the advice. I'll give it a try. You are quite right, the brightest part of the sky with the sun trying to burst through the clouds, is totally blown. At a 750th sec at f8 and ISO 100, there was no way I could have reduced exposure significantly without introducing unacceptable (and difficult to remove) noise in the shadows. This is the typical shot where autobracketing would have been useful. It so happened I did have a tripod in the back of the car, but by the time I got it out and set it up and searched for the remote cord, the mist has lifted and the scene was no longer as interesting. Nevertheless, I should have taken a series of handheld autobracketed shots. The bunglings of an amateur I'm afraid.
Title: Today's DSLR should have another exposure mode
Post by: Ray on June 09, 2006, 01:46:29 am: Quote
Add a Curves’ adjust layer (80% Opacity and Normal blend mode) which then will carry the inverted selection as a layer mask. The curve itself is a quite special one; it is defined by the following 6 anchor points for Input/Output = 31/40, 56/78, 83/124, 114/172, 147/212 and 180/240.
[a href=\"index.php?act=findpost&pid=67636\"][{POST_SNAPBACK}][/a]

Well, I followed some of your advice. Couldn't find that special curve with input/output anchor points of 31/40 etc. Where's that hidden ?

The finished image (finished at this stage, anyway) looks like this. This is a screen grab of the 'proof cololors' image in relation to Epson Premium Lustre (paper color on) and K2 inks on the 7600, perceptual rendering intent.

[attachment=672:attachment]

On the other hand, a saturation rendering intent might be more appropriate . What do you think?

[attachment=673:attachment]
Title: Today's DSLR should have another exposure mode
Post by: Ray on June 09, 2006, 03:28:00 am: Just to get things into perspective, here's the monitor image with no proof colors, but same adjustments. Satuaration intent seems to be closer to the 'non-proof color' image to my eyes.

[attachment=674:attachment]
Title: Today's DSLR should have another exposure mode
Post by: PeterLange on June 09, 2006, 02:59:30 pm: Quote
Just to get things into perspective, here's the monitor image with no proof colors, but same adjustments. Satuaration intent seems to be closer to the 'non-proof color' image to my eyes.

[attachment=674:attachment]
[{POST_SNAPBACK}][/a] (http://index.php?act=findpost&pid=67757\")
Ray,

I’m sincerely glad that clipping (due to exposure) does not only happen to me. And in particular I’m glad that my remote proposal obviously did not went so wrong. As a pure amateur, I find that the last rendition communicates the mood of the scene very well. For example, I could imagine that if your family shared this moment, they’ll love it. My eldest daughter would probably suggest to try to crop & isolate the left half (x 0 to 505 or so); but, that’s definitively not the point with an image that was selected and generously offered for HDR test purposes.

Out of interest, at which settings did you finally arrive in ACR and in Photoshop?

IF of interest at your side:
/> I had outlined some thoughts on tonal settings in ACR [a href=\"http://www.outbackphoto.com/tforum/viewtopic.php?TopicID=1991]here[/url]. Though I have to admit that I left discussion for some reasons. Anyway, above text could be seen as a supplement, in case that the global tonal controls cannot compensate enough for dyn. range compression (scene to monitor) without causing damage.

/> Referring to this special tone curve (31/40, etc.), in fact it comes from ACR’s presets. It was just extracted to use it Photoshop; it’s an all-brightening slightly S-shaped curve - a very nifty thing (as suggested here (http://www.prophotocommunity.com/ubbthreads/showflat.php/Cat/0/Number/387193/an/page/page//vc/1)) and it has become a key part of my toolbox.

Peter

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Title: Today's DSLR should have another exposure mode
Post by: Ray on June 10, 2006, 12:16:31 pm: Quote
Out of interest, at which settings did you finally arrive in ACR and in Photoshop?
[a href=\"index.php?act=findpost&pid=67787\"][{POST_SNAPBACK}][/a]

Peter,
I can't remember precisely. This is the sort of image which can be reworked many ways, but approximately the ACR settings were, for the latest version above; minus 2EC, zero brightness, shadows and contrast (but maybe contrast was -50) and I might have used an ACR preset linear curve. I then ctrl clicked on the RGB channel, inverted selection and applied an adjustment curve with 80% opacity. The curve would have been similar to the one pictured above. I then selected the lower part of the image, to the base of the tree and including the cows, with the lasso tool and 40 pixel feather. Used levels to brighten the lower part as though it were a separate picture, applied a bit of 'local contrast enhancement' with unsharp mask to the selected part only and bumped up general saturation to +7 with the hue/sat control.

I wouldn't say this is the final image. There's a slight blocking of shadows in the foreground which can be avoided. It's a good image to play around with though. I'm not keen on cropping it but I wish I could soften the abruptness of the blown part of the sky.

The curve you've described with specific anchor points doesn't seem to work for this image.
Title: Today's DSLR should have another exposure mode
Post by: PeterLange on June 11, 2006, 06:27:57 pm: Quote
I wouldn't say this is the final image. There's a slight blocking of shadows in the foreground which can be avoided. It's a good image to play around with though. I'm not keen on cropping it but I wish I could soften the abruptness of the blown part of the sky.
Ray,

In my eyes that’s an excellent rendition of this image.

And I’m glad that we could approach our views during discussion.

So long! Peter

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Title: Today's DSLR should have another exposure mode
Post by: Ray on June 12, 2006, 08:50:39 am: Thanks, Peter for sharing some Photoshop techniques. I actually like this photo despite the flaw of a large blown highlight. For me, of course, there's a background experience that I'm aware of, but the viewer is unlikely to be aware of.

The scene is in far North Queensland (Australia), in a World Heritage area, and the mist is rising from the Daintree river, barely visible on the extreme right of the shot. I was driving along an unidentified road going to a mystery destination in what I thought was a national park. I was therefore surprised to come across a couple of grazing cows.

I learned later that the road led to the farm house of a dairy farm that existed before the area had been declared World Heritage.
Title: Today's DSLR should have another exposure mode
Post by: Cyril on July 07, 2006, 08:28:33 am: Interesting discussion all around.

For those using dcraw/ufraw, you might be interested by this webpage I put up a while ago:
Highlight recovery with ufraw (http://people.zoy.org/~cyril/ufraw_highlight_recovery/)

I find that I can recover quite a lot of information from the highlights this way, without getting those weird colour casts that tend to appear usually.

Regards,
Cyril
Title: Today's DSLR should have another exposure mode
Post by: Guillermo Luijk on May 16, 2007, 07:46:51 am: Quote
But what about the centre of the sun? That white spot is bigger than a mere specral highlight. Whatever the setting in ACR, it's 255,255,255, even with -4EC, which is okay by me. I'd expect the centre of the sun to be a blown highlight, but I was curious as to what a linear conversion would reveal and was very surprised to find that even that centre white spot does not seem to be blown. It's just a neutral white. The image appears to be actually underexposed by about 1/4 of a stop. That's close enough for me .

[attachment=601:attachment]
[{POST_SNAPBACK}][/a] (http://index.php?act=findpost&pid=66459\")

Old but interesting post. I wonder if the sun in Ray's linear histogram is really not blown in any channel. The histograms look blown to me (see that little peak right in the end of the histogram line), but this does not happens in the end of the histogram as level values seem to have been corrected afterwards by some scaling (probably WB).
This happens sometimes if a RAW developer with less than 1.0 multipliers for the WB is used (like DCRAW for instance).
This is a sample of histogram with green channel clearly blown but using -H 0 (no-clip): WB multipliers in DCRAW {R,G,B}={0.586287, 0.421032, 1.000000}:

(http://img150.imageshack.us/img150/3669/41tungshisvs9.gif)

Another issue: did you know that scaling from 12-bit RAW to 16-bit in DCRAW uses a slightly greater than 16.0 multiplier?. Maybe this happens only on Canon cameras, but Dave Coffin confirmed this to me as I saw 16-bit histograms with peaks not equally spaced in 16 levels but a bit more (~17 let's say). That means (at least Canon cameras) don't make use of the full 12-bit: 0..4095 range.

If you want a tool to analyse detailed 15-bit histograms find it here:
[a href=\"http://perso.wanadoo.es/gluijk/soft/histo.htm]http://perso.wanadoo.es/gluijk/soft/histo.htm[/url]
Title: Today's DSLR should have another exposure mode
Post by: bjanes on May 16, 2007, 10:48:58 am: Quote
Old but interesting post. I wonder if the sun in Ray's linear histogram is really not blown in any channel. The histograms look blown to me (see that little peak right in the end of the histogram line), but this does not happens in the end of the histogram as level values seem to have been corrected afterwards by some scaling (probably WB).
This happens sometimes if a RAW developer with less than 1.0 multipliers for the WB is used (like DCRAW for instance).

Another issue: did you know that scaling from 12-bit RAW to 16-bit in DCRAW uses a slightly greater than 16.0 multiplier?. Maybe this happens only on Canon cameras, but Dave Coffin confirmed this to me as I saw 16-bit histograms with peaks not equally spaced in 16 levels but a bit more (~17 let's say). That means (at least Canon cameras) don't make use of the full 12-bit: 0..4095 range.

[{POST_SNAPBACK}][/a] (http://index.php?act=findpost&pid=117848\")

For practical reasons, most digital cameras do not make use of the full 12 bit (0..4095) range. The pixel of a digital sensor can be likened to a bucket (or well) that collects electrons. When the pixel has collected all the electrons it can hold, this is called [a href=\"http://www.photomet.com/library/library_encyclopedia/library_enc_fwcapacity.php]full well[/url]. The output of a CCD sensor is voltage, which is amplified and presented to the analog to digital converter (ADC). A 12 bit ADC has possible outputs of 0..4095. This output is in units of analog to digital units (ADUs) and this represents the raw pixel value. The amplification is chosen so that at the full well of the sensor, the output of the ADC is at or near its maximum as explained in the reference. In practice, it may be difficult to obtain an exact match, so a little leeway may be allowed and the output of the ADC may not quite 4095. In addition, the sensor response may not be linear near full well, and only the linear portion of the sensor may be mapped to the ADC output.

To test the range of the ADC that is used, one can make a series of exposures until the sensor is saturated and the ADU value no longer increases. DCRaw is often used to examine the contents of the raw file, but I have found that Iris (http://www.astrosurf.com/buil/us/iris/iris.htm) is more convenient, since it has a graphical interface and also has tools to analyze the resulting conversion. To use Iris, one loads the raw file and performs a demosaicing operation, which renders the raw file into an RGB 12 bit form. No white balance is applied, and one can examine the values in the raw channels by placing the cursor over the area of interest. If desired, a white balance can be applied with multipliers. The file can be converted to the Photoshop 15 bit format (0..32,768) by multiplying the channels by 8 or to a conventional 16 bit file by multiplying by 16.

With my Nikon D200 (which uses a CCD), the ADU output at saturation is about 4009, rather than 4095. In the case of Ray's sun disk, the sensor is most likely fully saturated and there is no "underexposure". Canon cameras use CMOS rather than CCD and the pixel outputs a pixel value directly than presenting a voltage to an ADC, but the principle is similar.

Bill