Lab values and color management issues

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russellcottrell
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Registriert: Sa 26 Jul 2014 10:13
Wohnort: California

Lab values and color management issues

Beitrag von russellcottrell »

Hello; I am having unexpected results viewing an image’s Lab values when assigning and converting ICC color profiles. The picture’s Lab color values in the Picture Info panel depend on the profile set in Edit - Options - Color Management - Standard - RGB. If it is set to ProPhoto, for example, the numbers for images that have ProPhoto assigned are correct. But after converting to sRGB, for example, the appearance of the image does not change, and the Lab numbers are correct if it is saved and opened in another application, but the Lab numbers displayed in PhotoLine’s Picture Info panel are incorrect. UNLESS the profile in the Color Management dialog is changed to sRGB, then the numbers change to the correct ones. This also happens when creating a new image with a profile different from the one in the Color Management dialog.

Example: Color Management - Standard - RGB is set to ProPhoto. Create a new image with ProPhoto as the color profile, and flood fill it with Lab 50, -40, 40. The Picture Info numbers are Lab 50, -40, 40 and RGB 72, 109, 49 (one digit away from Photoshop, close enough). Now Tool - Color - Convert With Color Profile to sRGB, Relative Colorimetric, Use Blackpoint Compensation. The appearance of the image does not change, but the Picture Info numbers change to Lab 56, -86, 56 (incorrect) and RGB 51, 136, 44 (correct). If you save the image and open it in Photoshop, it still looks o.k., and the numbers are Lab 50, 40, -39 (once again, one digit away, close enough) and RGB 51, 136, 44 (correct). In PhotoLine, you have to change the profile in Color Management - Standard - RGB to sRGB to get the Lab numbers to correctly display 50, -40, 40. It does not appear to affect the RGB numbers, or the image itself, just the display of the Lab numbers

The default numbers when the Standard - RGB profile is set to System appears to be sRGB.

This happens whether or not I am using Little CMS. It is true in both 19.51 and 20.01, 32 and 64-bit versions; Windows 7.

Thank you,

—Russell
bkh
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Beiträge: 3674
Registriert: Do 26 Nov 2009 22:59

Re: Lab values and color management issues

Beitrag von bkh »

russellcottrell hat geschrieben: So 12 Feb 2017 23:08 Example: Color Management - Standard - RGB is set to ProPhoto. Create a new image with ProPhoto as the color profile, and flood fill it with Lab 50, -40, 40. The Picture Info numbers are Lab 50, -40, 40 and RGB 72, 109, 49 (one digit away from Photoshop, close enough).
Looks like the problem already arises at this stage. Choose sRGB as the RGB standard in PL's preferences, and PL will convert the Lab colour to sRGB values (regardless of the document/layer profile); choose ProPhoto as the standard profile, and PL will use ProPhoto RGB values. Looks like a bug in PL. The Lab colour should be converted according to the layer profile, not the standard profile.

Cheers

Burkhard.