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Author Topic: Lightroom Colour Space  (Read 7759 times)

digitaldog

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Re: Lightroom Colour Space
« Reply #20 on: February 25, 2015, 03:01:20 pm »

The data and histogram I see without Soft Proof on is reflecting output of what?
Melissa RGB. ProPhoto RGB with a different TRC than ProPhoto (2.2) BFD.
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The thing about LR is that images and their edits are in a constant state of perpetuity until the edits are committed to export to a tiff or jpeg so while in LR with Soft Proof turned off the data reflected in the histogram and "%" numbers have very little connection to what's reflected in the preview with regard to measuring and defining the preview through HSL or RGB analysis. Do I have that correct?
When you soft proof, what you see is what you will get, visually and numerically after rendering through LR. Setup a soft proof for Epson 3880 Luster, that's what you get to see before a conversion to that output color space. Since you have asked LR to simulate the appearance, numbers and histogram (based on a RI as well), AND you decide at this point to edit that data, the rational of the workflow process is now set for you: you apply output specific (or different from the master) edits so based on that new appearance and path, to a Proof Copy. ACR can't do that.
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I never tried changing Soft Proof setting from ProPhotoRGB to another matrix profile to test to see a preview change, but if I understand you right (despite my doubts I'm able to), if I decide to Soft Proof to a printer profile with edits made using Soft Proof set to ProPhotoRGB on the "Make This The Proof" (I assume this means the master IS the proof) selection, the printer Soft Proof will only reflect the edits applied/encoded on the original master when Soft Proof was off and reflecting Linear with Adobe Default settings applied. Is that right?
The Proof Copy workflow has nothing to do with the kinds of profiles, color space etc. You've got a master image shown to you one way in Melissa RGB. You switch that by setting a soft proof based on another color space. Either kind or profile, working space or output. The image on screen might change, it might not (toggle from ProPhoto to Adobe RGB (1998) or even sRGB, depending on the image, it might appear the same on-screen). The numbers and histogram will change. But you've told LR you want to work in another color space (fine) but further you now tell LR you want to apply an edit. Boom, you must and should do this on a proof copy! The master is untouched just as if you duplicated an image in PS and applied adjustment layers for output specific edits on the copy.
All the other comments to follow you've made are immaterial to the above workflow you appeared to misunderstand and criticize:
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And right behind it in annoyance is the subsequent warning dialog box after making the first edit asking if I want to make this the Proof or Proof Copy which I have no idea what the differences are.
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Tim Lookingbill

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Re: Lightroom Colour Space
« Reply #21 on: February 25, 2015, 04:36:46 pm »

So a Proof Copy is not a Virtual Copy. IOW a duplicate of the master isn't made by either choosing "Make This The Proof" or "Proof Copy" when turning on Soft Proofing and getting that dialog box prompt.

I was under the impression that the xmp edits were the non-destructive method that gets embedded in the master over having to create a duplicate using Virtual Copy.
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digitaldog

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Re: Lightroom Colour Space
« Reply #22 on: February 25, 2015, 04:39:22 pm »

So a Proof Copy is not a Virtual Copy.
It is a specific type of VC yes.
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torger

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Re: Lightroom Colour Space
« Reply #23 on: March 10, 2015, 04:51:00 am »

I'd just like to add that gamma can be a quite confusing concept these days. This is because much of it just relates to internal color math and is rarely something the photographer needs to bother with.

In digital photography the purpose of gamma encoding is to make best use of integer math so you don't waste most of your integer steps on the very last bit of highlights. Since Lightroom and most recent photo software works in floating point space gamma has lost its meaning for the internal math. Lightroom uses ProphotoRGB primaries / RIMM space but don't need to apply the 1.8 gamma as it's floating point. Then this internal prophoto floating point image is converted via the display's ICC profile so you'll see the colors the display can handle. I assume the conversion is perceptual intent, but I'm not sure. Then there's softproofing of course, discussed above.

However, the curves tool and histogram must be displayed with a gamma, otherwise the topmost stop would take up half of the space and as our eyes have an exponential sensitivity that would not make sense. I don't know what Lightroom uses for the curves and histogram (and the 0-255 values under the picker), but I would expect gamma 2.2.

The most common file formats, 8 bit jpeg and 16 bit tiff, are both integer format so they need gamma encoding, this is made automatically at export so the user doesn't need to care. Many applications today can export/import floating point tiff, and what happens if you export a floating point tiff with ProphotoRGB color space? Gamma enconding makes no sense in floating point, so the correct way would be to encode linear, embed an ICC profile which looks like the ProPhotoRGB but has linear gamma. Defacto standard has however become that if floating point assume linear gamma and ignore gamma of the profile, so it's not uncommon that a floating point tiff contains the original ProphotoRGB icc profile with gamma, but if you apply the gamma the image will render incorrectly.

Anyway if digital color management had been created today when floating point math is always available and fast we would probably talk much less about gamma and color spaces with gamma. It still makes sense with integer gamma encoded formats for compression, but the whole color management pipeline could be floating point.
« Last Edit: March 10, 2015, 05:02:39 am by torger »
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Simon Garrett

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Re: Lightroom Colour Space
« Reply #24 on: March 10, 2015, 11:45:16 am »

I'd just like to add that gamma can be a quite confusing concept these days. This is because much of it just relates to internal color math and is rarely something the photographer needs to bother with.

In digital photography the purpose of gamma encoding is to make best use of integer math so you don't waste most of your integer steps on the very last bit of highlights. Since Lightroom and most recent photo software works in floating point space gamma has lost its meaning for the internal math. Lightroom uses ProphotoRGB primaries / RIMM space but don't need to apply the 1.8 gamma as it's floating point. Then this internal prophoto floating point image is converted via the display's ICC profile so you'll see the colors the display can handle. I assume the conversion is perceptual intent, but I'm not sure. Then there's softproofing of course, discussed above.

However, the curves tool and histogram must be displayed with a gamma, otherwise the topmost stop would take up half of the space and as our eyes have an exponential sensitivity that would not make sense. I don't know what Lightroom uses for the curves and histogram (and the 0-255 values under the picker), but I would expect gamma 2.2.

The most common file formats, 8 bit jpeg and 16 bit tiff, are both integer format so they need gamma encoding, this is made automatically at export so the user doesn't need to care. Many applications today can export/import floating point tiff, and what happens if you export a floating point tiff with ProphotoRGB color space? Gamma enconding makes no sense in floating point, so the correct way would be to encode linear, embed an ICC profile which looks like the ProPhotoRGB but has linear gamma. Defacto standard has however become that if floating point assume linear gamma and ignore gamma of the profile, so it's not uncommon that a floating point tiff contains the original ProphotoRGB icc profile with gamma, but if you apply the gamma the image will render incorrectly.

Anyway if digital color management had been created today when floating point math is always available and fast we would probably talk much less about gamma and color spaces with gamma. It still makes sense with integer gamma encoded formats for compression, but the whole color management pipeline could be floating point.

AFAIK it's as you say, except that histograms and colour picker use sRGB's TRC, so roughly 2.2 gama except at the black end.  (The colour picker uses %, not 0-255).  The develop module working space is ProPhoto with linear TRC as you say, library module displays the cached previews, which are in Adobe RGB and web module (I seem to recall) uses sRGB. 
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Tim Lookingbill

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Re: Lightroom Colour Space
« Reply #25 on: March 10, 2015, 12:03:35 pm »

I wonder which histogram linear ProphotoRGB vs output gamma when turning on Soft Proof reflects LR's built-in highlight compression that can't be turned off?
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digitaldog

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Re: Lightroom Colour Space
« Reply #26 on: March 10, 2015, 01:32:32 pm »

Melissa RGB uses the sRGB TRC (it is not a gamma curve). The underlying data is processed using a linear gamma (1.0). Not sure why anyone would need to see this but it is possible to build and use a 1.0 TRC gamma variant of ProPhoto RGB within LR (build one in Photoshop's Color Settings). Most users don't have to worry a lick about gamma or the TRC of any of the spaces they are working with. 
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