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B
B__R
Participant
January 16, 2012
Question

Color Management in Lightroom 4

  • January 16, 2012
  • 1 reply
  • 13517 views

By default, Lightroom uses the Pro Photo color space "with the same gamma curve as sRGB," according to something I read somewhere. Now Pro Photo is a very wide color space, wider than any monitor can display - even my wide-gamut (Adobe RGB) monitor. If I adjust the color in an image to very high saturation, then at some point in the adjustment I must reach a part of Pro Photo that cannot be displayed on my monitor so I would expect to stop seeing any changes after that point. Yet I continue to see changes all the way up to saturation 100. So this has something to do with the sRGB curve that is somehow mapping those out-of-gamut colors to something that can be displayed.

I'd appreciate some explanation of this process, or any useful links.

Thanks.

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    1 reply

    TheDigitalDog
    TheDigitalDog
    Inspiring
    January 16, 2012

    LR and ACR process data with ProPhoto primaries and a linear (TRC 1.0 gamma) encoding. The histogram and RGB percentage values use a 2.2 TRC (Melissa RGB).

    In terms of the disconnect between the display gamut limit and the editing space, not much you can do. If you are editing by moving a slider and all of a sudden you stop seeing the edit affect the preview, back off, you are probably editing colors outside display gamut. Also keep in mind, there are ‘colors’ defined in ProPhoto RGB that are not visible (and technically can’t be called colors).

    Author “Color Management for Photographers" & "Photoshop CC Color Management/pluralsight"
    B
    B__RAuthor
    Participant
    January 17, 2012

    Thanks for the reply. The thing is I don't necessarily stop seeing the edit affect the preview. Here's an experiment I did - I imported a raw (Adobe RGB tagged) image of grass into LR. Recall that I have a monitor that basically covers all of Adobe RGB. I notice that as I move the saturation slider I can see changes in the green, including between saturation values from 50 to 100. If I soft-proof the image using the Adobe RGB profile, it indicates that basically the whole image is out-of-gamut already at a saturation value of 50. Yet I can continue to change the saturation beyond 50 with noticeable results.

    I'm coming to the conclusion that LR continues to map the out-of-gamut colors down to Adobe RGB, using some particular rendering intent (Perceptual?). As the colors get more and more out-of-gamut, the mapping changes so the image changes. Make sense?

    TheDigitalDog
    TheDigitalDog
    Inspiring
    January 18, 2012

    I realize that a raw image has no embedded color profile and should not have confused the issue. BTW - my camera identifies the raw file with the in-camera setting for color space and my usual raw image processor (Capture NX2) uses that embedded profile to define the color space of the image, unlike LR which is always using Melissa RGB. It can be changed in NX2, but it uses the tag as the initial color space definition.

    I was looking at the gamut overlay in the main image window that you invoke via the soft-proof panel on the top right of the program window. I did not realize that there was one on the "left" also. Will have to check that out tonight as I don't have LR here at work. Can you be more specific as to where that second gamut overlay is and how it is invoked?

    Thanks.


    The Left Gamut overlay is kind of useless IMHO. It compares the display gamut to Melissa RGB. The Right Gamut overlay compares Melissa RGB to whatever profile you select. More useful. The Left overlay could be more useful if it was based on the profile you select (show me how my sRGB-like display gamut compares to the gamut of a profile I just selected to make a print). But alas, it doesn’t do this. I’m trying to find out the logic of the current behavior. I feel it would be far more useful in Develop without a soft proof since you are editing in MelissaRGB (kind of, it is 1.0 TRC), and seeing how that color space is out of gamut compared to the display would be real useful.

    Author “Color Management for Photographers" & "Photoshop CC Color Management/pluralsight"
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