How can I turn an ICC profile-based color shift into a 3D LUT or abstract profile?
Asked 11/12/2017
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2 answers
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I have 48-bit TIFF images in ProPhoto RGB, and I can get a desired color transformation by assigning a slightly modified input profile instead of the normal ProPhoto RGB profile. I know that reassigning profiles is not the proper way to represent a creative color transform.
What I want is a reusable transform that produces the same result, ideally as either:
- a 3D LUT, or
- an abstract profile
In principle, I want a transform equivalent to taking RGB values in the original working space, applying the color change implied by the alternate profile, and then packaging that as a standalone color transform. I’m comfortable writing code if needed.
What practical workflow can I use to build such a LUT/profile from the existing profile-based transformation?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
8y ago
2 Answers
1
You can do this by creating an RGB Color Cube as a .tif (or whatever lossless format you prefer), taking it into Photoshop, applying the transform to the image, then saving it back out. I have one that is 64x64x64:
So open that in Photoshop and tell it that it's in the source color space you want to transform from. (You may need to tell it to ignore the profile that's attached if there is any. Not sure what uploading it here does to the image.) Then do whatever you were doing to convert to the new color space. Save it back out in a loss-less, easy-to-read-with-code format. Then remove the color profile info if there is any, as that will cause it to render differently in the future. You can now use it as a 3D LUT.
Originally by user22895. Source · Licensed CC BY-SA 4.0
user22895
8y ago
0
Generated from our catalog & community — verify before relying on it.
A practical way is to capture the transform as a 3D LUT using a color cube image.
Create an RGB color-cube test image (for example a 64×64×64 cube saved as a lossless TIFF). Open it in Photoshop and assign the original/source profile you want to transform from. Then apply the same profile-based conversion or reassignment workflow that gives you the desired look. Save the transformed cube back out as a lossless file.
That saved cube now encodes the mapping from the original RGB values to the transformed RGB values, so it can be used as a 3D LUT.
Important points:
- Use a lossless format.
- Make sure the cube is interpreted in the correct source color space before transforming it.
- Remove any embedded profile from the exported cube afterward, because keeping profile metadata can cause it to render differently later.
Based on the provided answers, this gives you a workable 3D LUT route. No confirmed method for generating a true Lab-to-Lab abstract profile was provided.
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