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Author Topic: Darkening, brightening and information loss  (Read 7960 times)
digitaldog
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« Reply #20 on: July 11, 2011, 02:30:17 PM »
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Improvements, I'd rather hope!

Yes, that’s why we edit images. But that has nothing to do with the terms used (destructive or non destructive).

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TIFF, probably none. But we were talking about non-destructive editing.

Exactly, so is it or isn’t it?
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Andrew Rodney
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« Reply #21 on: July 11, 2011, 04:42:59 PM »
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TIFF, probably none. But we were talking about non-destructive editing.

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Exactly, so is it or isn’t it?

Aside from any question of whether edits done in linear space are destructive to the "RAW" data (two thirds of which is new data generated by the demosaicing and not contained in the RAW file), the final, inevitable operation of gamma correction is certainly destructive, as shadows are stretched and highlights compressed. It is the price we have to (willingly) pay for a normal looking image, in a way similar to the fact that cellular attrition is the price of life.
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Hans Kruse
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« Reply #22 on: July 11, 2011, 04:49:34 PM »
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Aside from any question of whether edits done in linear space are destructive to the "RAW" data (two thirds of which is new data generated by the demosaicing and not contained in the RAW file), the final, inevitable operation of gamma correction is certainly destructive, as shadows are stretched and highlights compressed. It is the price we have to (willingly) pay for a normal looking image, in a way similar to the fact that cellular attrition is the price of life.

Although what you say is right, this is not what is meant by nondestructive Wink Nondestructive simply means that we can generate a final image from the RAW data without making a pixel version at any stage and the editing operations are pure metadata and not operations done on pixels. So until we export from Lightroom all we have is the original RAW file and a bunch of editing instructions!
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Schewe
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« Reply #23 on: July 11, 2011, 05:13:58 PM »
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I could be wrong but I don’t believe it uses floating point math for this (Schewe?) but I do know the order of edits is not in the order applied by the user but rather one optimized for image processing.

I could tell you but then I would have to kill you :~)

Actually, it's pointless to speculate and irrelevant whether or not ACR/LR using integer or floating point cause there's nothing a user can do to change it. And while you might think you know something, compared to the Bright Boys™ at Adobe, we all know nothing (as Sargent Schultz used to say). So, my suggestion is quit worrying about it.

As for the rest of the discussion, the order in which ACR/LR actually processes is fixed in a certain order by the engineers. Users can't change that and the order in which a user sets their settings has zero impact on the actual order of the processing.

In terms of non-destructive editing, that refers to parametric editing vs pixel based editing. Inside of ACR/LR is all edits are parameter edits and no pixel editing is done until you render an image. Photoshop can also do non-desructing editing via Adjustment Layers which also parametric edits.

Once you render a file, in ACR/LR or PS, subsequent edits will be data destructive to a certain extent. Some formats are also more destructive such as JPEG.

So, is the OP still in the building? Does this answer your question?

:~)
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elied
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« Reply #24 on: July 12, 2011, 06:07:50 AM »
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Although what you say is right, this is not what is meant by nondestructive Wink Nondestructive simply means that we can generate a final image from the RAW data without making a pixel version at any stage and the editing operations are pure metadata and not operations done on pixels. So until we export from Lightroom all we have is the original RAW file and a bunch of editing instructions!
True, but that is not what D.D. and the OP are talking about:
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@digitaldog: I’m not referring to the original, that’s not important (again, the Save As analogy). The question is about the new iterations FROM the rendered original. No damage?
I pointed out that even the first rendering - and even if it is written to tif/psd - will involve "damage" to the RAW capture data.

A distinction needs to be made here between "destruction", which is not what the OP asked about and the introduction of the term "non-destructive" already in the second post was OT and based on misunderstanding, and "damage" to data in the pipeline to an export.
« Last Edit: July 12, 2011, 06:21:28 AM by elied » Logged

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Alan Goldhammer
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« Reply #25 on: July 12, 2011, 07:08:24 AM »
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The OP's question (as I read it) was "will there be any artifacts introduced into an image as the result of LR processing steps" and not whether the underlying RAW file was altered in any way (we all know that as long as one stays in LR the RAW file is untouched).  Whether such artifacts are visible or not is maybe the key point here.  As Jeff points out, the order of operations and how they are accomplished is within the LR code design and we are not likely to find out from Adobe how this is accomplished.  I don't think anyone has answered the OP's question.
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John R Smith
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« Reply #26 on: July 12, 2011, 07:24:22 AM »
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The OP's question (as I read it) was "will there be any artifacts introduced into an image as the result of LR processing steps" and not whether the underlying RAW file was altered in any way (we all know that as long as one stays in LR the RAW file is untouched).  Whether such artifacts are visible or not is maybe the key point here.  As Jeff points out, the order of operations and how they are accomplished is within the LR code design and we are not likely to find out from Adobe how this is accomplished.  I don't think anyone has answered the OP's question.

That’s how I read it, too, Alan. And in general terms, yes of course LR can screw up your image in all sorts of ways if you push any of the processing steps to their extremes. The advantage is that in RAW at 16-bit you have a bit more headroom than if you were working with a pixel editor. I have accidentally produced all sorts of nasty artefacts in LR by ham-fisted editing, which if I had then rendered them to a TIFF would have been a permanent change. There is no especial voodoo charm to working in RAW, and this applies to any RAW editor, not just LR. My own 3FR files have an enormous amount of latitude, but I can still find the limits and they will then fall apart whatever the software.

But I think the OP’s post was very specific, and basically asked – if I darken the image using one slider (say EV or Brightness), and then lighten with another (say Shadow Fill) are the areas which started off at say 50, 50, 50 when lightened back to the same values compromised in some way? It seems to me that without documentation for the exact nature of the underlying process engine we have no way of knowing.

John
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digitaldog
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« Reply #27 on: July 12, 2011, 08:20:15 AM »
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I pointed out that even the first rendering - and even if it is written to tif/psd - will involve "damage" to the RAW capture data.

How so, the raw is read only.

The damage I’m asking about is the iteration of a TIFF (no reason to talk JPEG) from processing through LR or ACR FROM a rendered original, not raw.
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Andrew Rodney
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« Reply #28 on: July 12, 2011, 02:10:56 PM »
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That’s how I read it, too, Alan. And in general terms, yes of course LR can screw up your image in all sorts of ways if you push any of the processing steps to their extremes. The advantage is that in RAW at 16-bit you have a bit more headroom than if you were working with a pixel editor. I have accidentally produced all sorts of nasty artefacts in LR by ham-fisted editing, which if I had then rendered them to a TIFF would have been a permanent change. There is no especial voodoo charm to working in RAW, and this applies to any RAW editor, not just LR. My own 3FR files have an enormous amount of latitude, but I can still find the limits and they will then fall apart whatever the software.

But I think the OP’s post was very specific, and basically asked – if I darken the image using one slider (say EV or Brightness), and then lighten with another (say Shadow Fill) are the areas which started off at say 50, 50, 50 when lightened back to the same values compromised in some way? It seems to me that without documentation for the exact nature of the underlying process engine we have no way of knowing.

John

Pretty much, yes.  And after reading Schewe's comments, I think I am (or we are) just going to have to settle for not getting a detailed answer on this and trust that somehow LR will do the right thing and do what I want it to Smiley
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elied
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« Reply #29 on: July 12, 2011, 05:21:44 PM »
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Posted by: elied
I pointed out that even the first rendering - and even if it is written to tif/psd - will involve "damage" to the RAW capture data.
Posted by: digitaldog
How so, the raw is read only.

The file is not affected, but the data extracted from it is certainly changed. The application of a gamma correction TRC skewers and distorts the linear data and in this sense it can be seen as "damaging" it.
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digitaldog
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« Reply #30 on: July 12, 2011, 05:52:29 PM »
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The file is not affected, but the data extracted from it is certainly changed.

The last bit will involve "damage" to the RAW capture data. seemed to be directed at the raw, not the results. And I was again referring to a rendered image (not a raw). A rendered image processed from a rendered image. So it seems you are saying the rendered data from the rendered original is changed (damaged?).
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Andrew Rodney
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« Reply #31 on: July 12, 2011, 06:53:06 PM »
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I remember five years ago when LR was first released, one of the advantages claimed for it was that the integrity of the capture data is preserved because all calculations are made in linear space. I accept that claim as valid and justified. But the time inevitably comes when the conversion to ProPhoto RGB (gamma 1.Cool, Adobe RGB (gamma 2.2) or sRGB (gamma sort of 2.2 but not exactly) must be made. And at that point the data gets stretched at one end of the DR and squashed at the other end and generally turned into something that no mother sensor would recognize as her progeny.
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hjulenissen
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« Reply #32 on: July 13, 2011, 01:56:38 AM »
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When you have a raw sensor file in the Bayer format of 12-14 (linear) bits per channel and non-standard color filter response that you want to display on your typical display/printer of 8bits (2.2 gamma) sRGB/ARGB (standardized primaries) device, there is going to be some "loss" somewhere along the chain nomatter what. There is also going to be a radical change in numerical values, and this is a good thing as it makes the resulting image worth looking at.

The argument about Lightroom being "non-destructive" is that it separates image data (pixels) and editing instructions. Just like Microsoft Word is different from a typewriter - it does not save an image file containing the pixels of the rendered text. Rather, it works on a set of instructions that can be used to render the text at any time, but also do spell-checking and swapping the font. The original raw file is of course never touched, but the neatness of Lightroom is that it will read that raw file into memory, do your edits, and render the result to screen/export/printer. If you change one parameter, it will re-do this process (it may do internal optimizations, but analyzed as a user-oriented black-box I think this is correct). The important "philosophical" implication is that Lightroom isolates user 1. intent ("make the image brighter") and 2. image processing ("multiply all pixels by 2"). If the Adobe guys at some point find more clever ways to transform 1->2, they can do so (and atleast with the demosaicing in LR3, they did). They may theoretically do limited-precision integer processing in one version of Lightroom, and convert to single-precision floating point in another version as long as they deem that it gives only better end-result without compromising the intent of the original edit (this is mind-bogling because some users might actually want editing-induced banding and quantization and consider it a part of their edit. They may not be pleased with a radical new engine that does the processing "better").

Are you having problems with the end-results in Lightroom today? I guess that if you went to dcraw or something similar, you would have access to the ideal documentation of image processing (open-source code) so that you could put your mind at rest, or improve parts that you did not like.

-h
« Last Edit: July 13, 2011, 01:59:16 AM by hjulenissen » Logged
Alan Goldhammer
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« Reply #33 on: July 13, 2011, 06:37:47 AM »
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If you change one parameter, it will re-do this process (it may do internal optimizations, but analyzed as a user-oriented black-box I think this is correct). The important "philosophical" implication is that Lightroom isolates user 1. intent ("make the image brighter") and 2. image processing ("multiply all pixels by 2"). If the Adobe guys at some point find more clever ways to transform 1->2, they can do so (and atleast with the demosaicing in LR3, they did). They may theoretically do limited-precision integer processing in one version of Lightroom, and convert to single-precision floating point in another version as long as they deem that it gives only better end-result without compromising the intent of the original edit (this is mind-bogling because some users might actually want editing-induced banding and quantization and consider it a part of their edit. They may not be pleased with a radical new engine that does the processing "better").
They did change the processing with LR 3 and for those of us who had a lot of processed images using LR2, this is duly noted when you are in LR and the new sharpening and noise reduction capabilities argue for the redoing of some images.  Who knows what will happen with LR 4 when it appears (other than the longed for soft proofing feature that many are clamoring for).
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Hans Kruse
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« Reply #34 on: July 13, 2011, 09:32:27 AM »
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They did change the processing with LR 3 and for those of us who had a lot of processed images using LR2, this is duly noted when you are in LR and the new sharpening and noise reduction capabilities argue for the redoing of some images.  Who knows what will happen with LR 4 when it appears (other than the longed for soft proofing feature that many are clamoring for).

That's correct, but I think it is worth noting that the old algorithms known as process version 2003 were kept as default and only if you wanted the new algorithm 2010 you would choose to do so. Old pictures were 2003 by default, so I Adobe did a good thing not to change the look of the pictures by one upgrade.

I did change all my pictures to process version 2010 since I felt the improvement was worth the change.
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kenlip
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« Reply #35 on: July 16, 2011, 05:54:48 AM »
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After reading this thread so far, I have had to rephrase the OP's question in my mind to be sure that I am fully understanding what he is asking.   I thought I might share with you how I see it.


Assume ...

I have a file - let's call it Test.RAW.  I make two copies of it, one called Test_E_F.RAW and the other called Test_F_E.RAW

I open Test_E_F.RAW in Lightroom, wang  the Exposure slider to the left a certain amount and then wang the Fill slider to the right a certain amount

I then open Test_F_E.RAW and reverse the order of the wanging - first the Fill slider to the right and then the Exposure slider to the left, both by the identical amounts I did for Test_E_F.

The Question:   Will there be any difference in the two images, even before exporting them into a usable format such a TIFF?

The OP seemed to believe there might be.  He explained why he thinks so, based on the algorithms/maths that Lightroom MAY be using, and suggested that, if there is a difference, it could be important to make adjustments in a particular sequence.

So far the answers seem to have been to the effect that Adobe has (probably!) considered the maths and will compensate for any anomalies that might arise from the sequence in which the changes are applied.  Therefore, Test_E_F and Test_F_E will be identical, and will produce identical images when exported from Lightroom into a different format e.g. TIFF or if they are printed from Lightroom.

Of course, even after all the slider wanging, the three files - Test.RAW, Test_E_F.RAW and Test_F_E.RAW are exactly as they were originally and will never be changed irrespective of what sliders are wanged in Lightroom or what format is used when exporting the images from Lightroom.


I hope this rephrasing of the OP's question helps.
Ken

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sandymc
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« Reply #36 on: July 16, 2011, 06:37:26 AM »
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So far the answers seem to have been to the effect that Adobe has (probably!) considered the maths and will compensate for any anomalies that might arise from the sequence in which the changes are applied.  Therefore, Test_E_F and Test_F_E will be identical, and will produce identical images when exported from Lightroom into a different format e.g. TIFF or if they are printed from Lightroom.

The two TIFF output images will be identical, but it has nothing to do with the math or any compensation for anomalies. As I pointed out in reply 8 above, because LR aways starts from the original data and processes in a fixed sequence, if the various sliders are in the same position, then the output will be the same. How many time the sliders have moved in whatever direction doesn't matter. This would be the case even if you used 4-bit integer arithmetic - the images would look terrible, but they would be identical.

Sandy
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Hans Kruse
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« Reply #37 on: July 16, 2011, 08:44:00 AM »
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No, the images will not be identical which you can easily test. Fill light is not the inverse of exposure. As also brightness is not either.
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Richowens
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« Reply #38 on: July 16, 2011, 03:55:52 PM »
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Hans,

If the slider movements are the same amount then the two files will be the same. It matters not what order the movements are made, just the amount.

Rich
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Hans Kruse
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« Reply #39 on: July 16, 2011, 04:30:41 PM »
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I didn't mention order... As said above fill light is not the inverse of exposure and the also btw. have different metrics, so an equal amount does not make sense. Exposure sets the white point, fill light lifts the shadows and does not move the white point.
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