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Author Topic: Will Michael revisit ETTR?  (Read 56085 times)
John Camp
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« on: August 12, 2011, 06:50:38 PM »
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Given the the controversy over the past couple of weeks, it would be interesting to see an expanded article that would summarize (and simplify) the various ETTR possibilities -- or perhaps two or three articles summarizing different views. As I have mentioned in my comments, I'm not so much interested in an engineering discussion, as in a "prescriptive" article or set of articles, that would deal with the when and how-to aspects of ETTR...if it's to be used at all. The various arguments have left me seriously uncertain about procedure...

JC   
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Ray
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« Reply #1 on: August 14, 2011, 01:41:28 AM »
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Given the the controversy over the past couple of weeks, it would be interesting to see an expanded article that would summarize (and simplify) the various ETTR possibilities -- or perhaps two or three articles summarizing different views. As I have mentioned in my comments, I'm not so much interested in an engineering discussion, as in a "prescriptive" article or set of articles, that would deal with the when and how-to aspects of ETTR...if it's to be used at all. The various arguments have left me seriously uncertain about procedure...

JC   

Well, I'll kick off with a few methods that have worked for me.

(1) First one should attempt to get the histogram and 'highlight flashing' as close as possible to the ideal RAW histogram, bearing in mind that the histogram is based upon a jpeg from the RAW data.

To do this, in my experience, requires adjusting the camera's jpeg settings so that the review image looks very lack-lustre and unappealing, so much so that you wouldn't want to show people the image you'd just taken in case they thought you didn't know what you were doing, or in case they got the impression their P&S was sooo.. much better than your expensive DSLR.
                                                                                                                                                                                                       
Such adjustment of the camera's jpeg settings will need a bit of experimentation. You might find you need to set contrast, saturation and sharpening at a minimum so that the 'highlight warning' doesn't flash when the image is still underexposed, from the RAW perspective.

(2) Buy a new camera which has a linear noise and dynamic range response (on the graphs at DXO Mark) that reduces by one f stop (or EV) for every doubling of ISO, so that there is no fundamental image quality advantage to increasing ISO.

The Nikon D7000 and Pentax K5 are in this category. With such a camera, you have only one worry regarding ETTR, and that's inadvertent overexposure at base ISO.

Unfortunately, the review image with this method can look even worse than the first method, if you've been underexposing at base ISO instead of using a higher ISO. It may be so dark you can hardly see it at all and you may have to flatly refuse to show it to anyone in order to protect your reputation.

(3)  Take the time and trouble to obtain a correct exposure for ETTR purposes before taking the shot. One effective way of doing this, using the camera's in-built exposure meter, is to set the camera to spot metering mode and, using a single focussing point, take a reading of the brightest part of the image you want to retain detail, then increase exposure by approximately 3 stops, depending on the model of your camera. Again you will have to experiment to determine whether that increase is 2.5 stops, 3 stops or 3.5 stops.

(4) Bracket either exposure or ISO. This is my favourite method because I can keep the review image looking bright and sparkly to impress the beautiful female subject I've just photographed.

There may be other useful techniques for achieving ETTR, but those are the ones I've tried and that work for me.
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Adam L
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« Reply #2 on: August 14, 2011, 07:14:23 AM »
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You should purchase the Camera to Print and Screen video series, it contains Michael's current view on this subject and more.   There is a segment on ETTR with Jeff showing examples of noise at both 'normal' exposure and ETTR exposures.  You can see the IQ differences, they're very material.   

I'm really enjoying the video series so far - 5 installments are available to view with more coming online over the next several months.   I feel that CPS is the most well thought out of all the Michael and Jeffrey series.  The ETTR segment is no exception.  I can see hours of preparation go into making each video segment.  Care was taken to make clear lesson goals delivered in a conversational manner.   Side by side comparisons, zooming in on image quality issues and basically explaining and showing at the same time are really great instructional tools.  This series is exceeding my expectations - it's both a learning and viewing experience.  I think you will find it enjoyable too.   Excellent editing helps - hat tip to Chris.
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douglasf13
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« Reply #3 on: August 14, 2011, 12:00:58 PM »
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Well, I'll kick off with a few methods that have worked for me.

(1) First one should attempt to get the histogram and 'highlight flashing' as close as possible to the ideal RAW histogram, bearing in mind that the histogram is based upon a jpeg from the RAW data.

To do this, in my experience, requires adjusting the camera's jpeg settings so that the review image looks very lack-lustre and unappealing, so much so that you wouldn't want to show people the image you'd just taken in case they thought you didn't know what you were doing, or in case they got the impression their P&S was sooo.. much better than your expensive DSLR.
                                                                                                                                                                                                       
Such adjustment of the camera's jpeg settings will need a bit of experimentation. You might find you need to set contrast, saturation and sharpening at a minimum so that the 'highlight warning' doesn't flash when the image is still underexposed, from the RAW perspective.

(2) Buy a new camera which has a linear noise and dynamic range response (on the graphs at DXO Mark) that reduces by one f stop (or EV) for every doubling of ISO, so that there is no fundamental image quality advantage to increasing ISO.

The Nikon D7000 and Pentax K5 are in this category. With such a camera, you have only one worry regarding ETTR, and that's inadvertent overexposure at base ISO.

Unfortunately, the review image with this method can look even worse than the first method, if you've been underexposing at base ISO instead of using a higher ISO. It may be so dark you can hardly see it at all and you may have to flatly refuse to show it to anyone in order to protect your reputation.

(3)  Take the time and trouble to obtain a correct exposure for ETTR purposes before taking the shot. One effective way of doing this, using the camera's in-built exposure meter, is to set the camera to spot metering mode and, using a single focussing point, take a reading of the brightest part of the image you want to retain detail, then increase exposure by approximately 3 stops, depending on the model of your camera. Again you will have to experiment to determine whether that increase is 2.5 stops, 3 stops or 3.5 stops.

(4) Bracket either exposure or ISO. This is my favourite method because I can keep the review image looking bright and sparkly to impress the beautiful female subject I've just photographed.

There may be other useful techniques for achieving ETTR, but those are the ones I've tried and that work for me.

I would add this:

(5)  Change your RAW converter, and/or expose appropriately for which ever RAW converter you use.
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Ray
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« Reply #4 on: August 14, 2011, 06:43:05 PM »
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I would add this:

(5)  Change your RAW converter, and/or expose appropriately for which ever RAW converter you use.

If anyone knows of a RAW converter that can recover more highlight detail and color than ACR (to a worthwhile degree, that is), I'd like to hear about it.

My favourite converter used to be RSP (Raw Shooter Premium). I simply preferred the rendition of microcontrast and color, and the arrangement of the controls. However, I did notice that recovery of highlights was not quite as good as ACR. I also found it easier to get more natural skin tones in ACR.

Each converter tends to have its strengths and weaknesses, and the fact one is simply familiar with the controls and use of one particular converter is itself a strength, from one's own perspective.

In two of the methods of achieving ETTR I've outlined above, (adjusting the camer's jpeg settings for contrast and color saturation, and/or taking a spot meter reading of the brightest area in the scene then increasing exposure by a set amount), it is necessary to experiment first using one's converter of choice to find out what settings to the jpeg image, and/or what degree of increase in exposure provide the most accurate result with regard to assessing the correct exposure for ETTR.
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douglasf13
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« Reply #5 on: August 14, 2011, 07:54:22 PM »
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If anyone knows of a RAW converter that can recover more highlight detail and color than ACR (to a worthwhile degree, that is), I'd like to hear about it.

My favourite converter used to be RSP (Raw Shooter Premium). I simply preferred the rendition of microcontrast and color, and the arrangement of the controls. However, I did notice that recovery of highlights was not quite as good as ACR. I also found it easier to get more natural skin tones in ACR.

Each converter tends to have its strengths and weaknesses, and the fact one is simply familiar with the controls and use of one particular converter is itself a strength, from one's own perspective.

In two of the methods of achieving ETTR I've outlined above, (adjusting the camer's jpeg settings for contrast and color saturation, and/or taking a spot meter reading of the brightest area in the scene then increasing exposure by a set amount), it is necessary to experiment first using one's converter of choice to find out what settings to the jpeg image, and/or what degree of increase in exposure provide the most accurate result with regard to assessing the correct exposure for ETTR.

That's exactly my point.  ACR is among the best, if not the best, at highlight recovery, and, if that is the program of choice, ETTR makes more sense.  With RPP, blown highlights aren't easily fixed, but bringing up exposure in the converter is quite a bit better, so ETTR isn't really necessary, especially if the trade off is color issues. 

One should expose with their converter of choice in mind.
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Guillermo Luijk
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« Reply #6 on: August 14, 2011, 07:56:29 PM »
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In two of the methods of achieving ETTR I've outlined above, (adjusting the camer's jpeg settings for contrast and color saturation, and/or taking a spot meter reading of the brightest area in the scene then increasing exposure by a set amount), it is necessary to experiment first using one's converter of choice to find out what settings to the jpeg image, and/or what degree of increase in exposure provide the most accurate result with regard to assessing the correct exposure for ETTR.

One should expose with their converter of choice in mind.

mmm if we agree that proper ETTR means no highlight clipping at all, I don't see why our particular RAW developer should have anything to say in the process of achieving ETTR in the camera. Proper ETTR is the same for all RAW converters: maximum RAW exposure before clipping, and all of them should produce similar results with perfectly ETTR'ed captures since no highlight recovery strategies are involved. I think this is again the discusion about using a RAW converter as something it was never intended to be, a RAW analyzer.

Regarding the settings for the most accurate histogram in the camera, modifying contrast, saturation, sharpness,... in the camera are peccata minuta (in particular a contrast curve should never produce/prevent any clipping). Modifying them will not help much since the most differentiating process between the RAW histogram and camera's histogram is by far white balance. So the way to make them look closer should be cancelling WB first.

Regards
« Last Edit: August 14, 2011, 08:00:28 PM by Guillermo Luijk » Logged

Ray
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« Reply #7 on: August 14, 2011, 10:54:10 PM »
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Regarding the settings for the most accurate histogram in the camera, modifying contrast, saturation, sharpness,... in the camera are peccata minuta (in particular a contrast curve should never produce/prevent any clipping). Modifying them will not help much since the most differentiating process between the RAW histogram and camera's histogram is by far white balance. So the way to make them look closer should be cancelling WB first.

Regards


Guillermo,
In my experience, changing the in-camera jpeg settings for constrast and saturation does have a significant effect on the appearance of the histogram.

Again, the histogram of different models of cameras may behave differently to the adjustments of the in-camera jpeg settings, but my experience with the Canon 5D was that the default jpeg settings, when shooting a typical landscape scene for example, might result in the entire sky flashing with the 'clipped highlight' warning, on the camera's LCD screen, despite the fact that such apparently clipped sky could be brought back to normal in ACR with the appropriate adjustments, and with no excessive and unnatural degree of cyan, too.

However, with contrast and saturation of the camera's jpeg set to a minimum, the histogram of a shot of the same landscape scene with same exposure would show just small areas of flashing in the brightest parts of the sky.

With such settings in place, one could then make a fairly accurrate assessment if the exposure had clipped some of the highlights. Small areas of 'flashing' indicated a good ETTR. No flashing at all indicated at least a small degree of underexposure. Moderate to large areas of flashing sky indicated that some clipping had taken place.

I'm speaking in the past tense because I no longer use this method. I prefer the less 'anal' approach of bracketing exposure or ISO.

I understand your UNIWB method would allow a slightly greater exposure to be used before clipping takes place. But such a method also results in a review image on the camera's LCD screen appearing  yukky. It also might create additional problems for the user in post processing, correcting for such a WB which is way out by a significant degree.

Just how much trouble does one want to take for marginal improvements in shadow noise? If I have the luxury of time on my side (and a tripod), and the scene is contrasty,  I'd rather bracket exposure and merge to HDR. If some movement has taken place during the bracketing, CS5 can sometimes handle it.

If I don't have a tripod but I'm really careful holding the camera steady, CS5 can usually handle the merging to HDR and correct for any minor misalignment.

Also, with cameras such as the D7000 and K5, ETTR is a non-issue above base ISO.

Regards

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jeremypayne
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« Reply #8 on: August 15, 2011, 06:09:25 AM »
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I understand your UNIWB method would allow a slightly greater exposure to be used before clipping takes place. But such a method also results in a review image on the camera's LCD screen appearing  yukky. It also might create additional problems for the user in post processing, correcting for such a WB which is way out by a significant degree.

Ray, I think you are inventing "additional problems" where none exist.
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Ray
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« Reply #9 on: August 15, 2011, 07:05:07 AM »
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Ray, I think you are inventing "additional problems" where none exist.

You mean it is not true that the review image will be yukky?

You mean that all converters and all users will have no problems perfectly correcting for the wrong WB?
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jeremypayne
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« Reply #10 on: August 15, 2011, 07:15:06 AM »
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You mean it is not true that the review image will be yukky?

You mean that all converters and all users will have no problems perfectly correcting for the wrong WB?

If you can't properly set a WB in your RAW editor of choice ... you probably shouldn't be shooting RAW ... or trying to ETTR ...

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Ray
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« Reply #11 on: August 15, 2011, 08:46:56 AM »
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If you can't properly set a WB in your RAW editor of choice ... you probably shouldn't be shooting RAW ... or trying to ETTR ...



Never heard that one before. "Why are you shooting Jpeg?" "Oh! Because I can't properly set the WB in the RAW converter. It's always off, for some reason."
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michael
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« Reply #12 on: August 15, 2011, 08:56:37 AM »
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What's to revisit?

If manufacturers did their job and gave us cameras that could automatically expose raw so that the image is just below important clipping (with a user selectable tolerance), and then "normalize" the image on the rear LCD and in the raw file metadata, we would have the absolutely optimum exposure possible for each and every shot. No need for anything else.

Isn't that what I wrote in the article?

Michael
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Peter_DL
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« Reply #13 on: August 15, 2011, 11:15:27 AM »
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I'm speaking in the past tense because I no longer use this method. I prefer the less 'anal' approach of bracketing exposure or ISO.

+1

Thinking about what I’m actually doing in practice, it is more a kind of "ETTR light" approach.  Means  to seek for a max exposure barely before we see those flashing highlight warning & relevant clipping with the camera luminance histogram (in-camera jpeg settings basically left at standard).
Then, if there is time and I’m in the mood, to bracket exposure in the + EV direction. +EV because at this starting point it seems to me unlikely that there’s already true Raw clipping involved.

To be honest, as much as I like theoretical part, my feeling is that any strict(er) ETTR concept & claim is stuck between a rock and a hard place, i.e. improving sensor performance & dynamic range, and improving "zero noise" HDR blending & tone mapping techniques.
 
Peter

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JeffKohn
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« Reply #14 on: August 15, 2011, 11:42:25 AM »
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You mean it is not true that the review image will be yukky?
It will have a green cast, but so what? At least the histogram will be more accurate. Is there some reason you think you need a color-accurate preview on the LCD? It's not like the LCD's are highly calibrated, anyways. If you're judging color based on the LCD preview you're asking for trouble.

Quote
You mean that all converters and all users will have no problems perfectly correcting for the wrong WB?
Any RAW converter worth using will allow you to set the WB without regard to the in-camera WB setting, so I'm not really sure what you're getting at here. And I for one don't see the point in constantly adjusting in-camera WB when it can be adjusted far more easily at the computer. Even if I didn't use UniWB, I'd just leave the in-camera setting on something like daylight, so I'm always going to be setting WB in the RAW converter anyways. For the most part I'm going to choose WB based on the aesthetic look I want for the image anyways (and if I want a 'neutral' WB I'll just shoot a gray card). So yeah, I would agree with Jeremy, anybody who think in-camera WB is important for anything other than judging exposure doesn't fully understand RAW.
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Guillermo Luijk
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« Reply #15 on: August 15, 2011, 12:08:57 PM »
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In my experience, changing the in-camera jpeg settings for constrast and saturation does have a significant effect on the appearance of the histogram.

And in my experience too, I never said it didn't. What I mean is that since WB is the main cause of camera vs RAW histogram disagreement, it doesn't make much sense fiddling with the saturation or contrast settings if we are using any non-neutral WB.
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ErikKaffehr
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« Reply #16 on: August 15, 2011, 12:22:53 PM »
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+1

BR
Erik

What's to revisit?

If manufacturers did their job and gave us cameras that could automatically expose raw so that the image is just below important clipping (with a user selectable tolerance), and then "normalize" the image on the rear LCD and in the raw file metadata, we would have the absolutely optimum exposure possible for each and every shot. No need for anything else.

Isn't that what I wrote in the article?

Michael

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digitaldog
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« Reply #17 on: August 15, 2011, 12:35:26 PM »
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You mean that all converters and all users will have no problems perfectly correcting for the wrong WB?

Considering the white balance has zero effect on the raw data, maybe (maybe because there are some users who will always have problems <g>).
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douglasf13
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« Reply #18 on: August 15, 2011, 01:27:27 PM »
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mmm if we agree that proper ETTR means no highlight clipping at all, I don't see why our particular RAW developer should have anything to say in the process of achieving ETTR in the camera. Proper ETTR is the same for all RAW converters: maximum RAW exposure before clipping, and all of them should produce similar results with perfectly ETTR'ed captures since no highlight recovery strategies are involved. I think this is again the discusion about using a RAW converter as something it was never intended to be, a RAW analyzer...
Regards


  It's because some converters deal with boosting exposure better than others, so sacrificing color for ETTR isn't always necessary or appropriate if you're using RPP with most newer cameras, and the makers of that program will tell you the same.  In fact, to quote Andrey Tverdokhleb, the designer of RPP, in regards to the A900 and RPP:

"...I meant using camera light meter (or external one if you care), but don't push histogram to the right and use camera light meter as it's intended, i.e. expose most important part of a picture around camera midpoint.  ETTR had some reasons for old cameras with low DR - noise was too close to the midpoint and we had to do this to minimize it. With late cameras which have over 9 stops of DR ETTR is very harmful for colors - midpoint is the most colorful place in A900 gamut and noise is not an issue there any more. In A900 gamut slowly narrowing down from midpoint to shadows and very quickly narrowing down from midpoint to highlights. This means that brightest stop of the camera range has most of colors gone forever and they cannot be restored with negative exposure compensation. I'd say all color critical parts should be below top 1.5 stops. Veiling glare from lens and sensor are the culprits here...Squeezing scene with high DR into sensor or film range is a totally valid approach when needed, same as exposing for shadows. ETTR however assumes that it's always better to shift histogram to the right, even when your scene is only 6 stops wide and sensor is 9.5 stops wide. You probably already noticed before that slightly underexposed shots can be amazingly colorful even after exposure correction and I definitely noticed that ETTR shots can be very dull after correction even if there was no clipping. So my point is that ETTR is not always better and shouldn't be used unconditionally. The whole approach that you need to pay attention only to highlights is very limiting - what's really important is were we place critical part of a picture on a sensor range. This critical part can be anywhere - in shadows, highlights or in the middle and we should understand that moving it closer to the middle gray will improve it's appearance and try our best...Gray point is the base point which light meter is calibrated to. There used to be an old film 18% gray standard (2.5 stops from saturation point at the top), than at some moment all vendors switched to 12.7% (about 3 stops). They all round up them differently, so there is some small variations, f.e. it can be 12.5%. Then they switched to even lower values. My A900 is about 10% gray (3.33 stops), but it looks like there is slight variations in different camera samples. This all is based on green channel only (not sure if they use same kind of green as on sensor though).

...Now recent crop of cameras like A900, D3X, 5D2 went even farther. A900 calibrated to 10% gray and picture exposed around this number will definitely look dark. Most likely vendors just optimized light meters to place gray point in the best spot of a sensor, which is a good thing - they can afford this because sensors are better and shadows are much cleaner now. Bad thing here is that pictures need to be compensated now. In RPP this means Compressed exposure correction about 0.7-0.8 for A900. It absolutely must be corrected!  Other converters do this behind a curtain and apply some exposure corrections automatically, usually badly and based on their own (mis)understanding, tone curve is getting involved so that's were all this confusion comes from. I completely disagree with this approach and in RPP you'll actually see picture exactly as it was captured and you need to define your correction specifically and make it default."
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Guillermo Luijk
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« Reply #19 on: August 15, 2011, 02:08:04 PM »
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Douglas, that endless speech has already been explained 1000 times in the forums. To believe all that I just need a pair of RAW files where it can be proved that colours get altered after proper ETTR. I have a feeling most people talking about colour shifts because of ETTR are just using clipped RAW files without knowing, or incorrect processing (this could include RAW converters handling eposure inapropiately, like Tverdokhleb suggests).

Some years ago I coded a program called Zero Noise that builds an output image from several input images, taking the most exposed non-clipped pixels. I consider valid a pixel as long as all three channel values in it are below a given safety threshold with respect to RAW saturation point. Do you know what threshold I decided to use by default? 90% of saturation in linear scale, that is only 0.15EV below RAW saturation. And I am pretty sure I could use 95% and the result would be the same.

Regards
« Last Edit: August 15, 2011, 02:11:24 PM by Guillermo Luijk » Logged

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