Understanding the essential operation of color transform is the most insightful thing I’ve done to understand color management. Once you get that, the rest is just stitching together transforms.
So, the camera records a scene, and that data has to be worked before it’s presentable in a way humans can appreciate. One of the things that needs to be done is to transform the data down from its spectral response to a colorspace that can be worked with or displayed. This is the first of a few color transforms, and it works like this:
- The raw data needs to be assigned a set of color primaries, usually 9 numbers that represent some notion of its color. These can be in a profile file (ICC or DCP), or come from a list stored internally by the raw processor.
- The transform is a two-step operation: The camera primaries are then used to transform the image data to the XYZ colorspace, which is based on the original 1931 CIE color-matching experiments. Really, the XYZ space is just a common intermediate in this process, keeps us from having to maintain camera profiles for every destination.
- The image data in XYZ is then transformed to the destination colorspace. This could be a working space like ProPhoto or Rec2020, or it could be direct to a display-sized colorspace like AdobeRGB or sRGB.
The above describes the general process of a transform, in the context of the first one that needs to be done out of camera space. I wrote something about a year ago that describes how transforms are generally used in raw procesing; you can find it here:
HTH…