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>ok. i can see it. xml is the right way to store these values. It will be fine to use the same file format. But where to store this file ? LibRaw ?

LibRaw will not store _additional_ DNG-related data due to three reasons:

* Copyright issues. LibRaw already have one set of DNG ColorMatrix tables derived from dcraw code. In this case we rely on Coffin's copyright clearance and free status of dcraw itself.
* the only programs that needs/uses two color matrices in DNG file are Adobe programs (Lightroom and Camera Raw). If you already use Adobe programs, you can also use free Adobe DNG converter.
* The 'DNG processing model' (quoting from Adobe staff member in dpreview forums) introduced in DNG 1.2 is much more complex, than in DNG 1.0/1.1. Should LibRaw store all (possibly copyrighted) Adobe color data in source code? I don't think so.

We (LibRaw team) dislike 'DNG processing model' because of very poor image quality produced by Adobe products (try compare with Raw Photo Processor): high noise levels (produced by mixing low noise Green with high noise Red channels), false colors (produced by using ProPhoto as internal space) and poor quality of color profiles (produced by small gamut of color targed used).

In my thoughts, the only place to store DNG-related color data is in DNG converter itself. I've added cam_xyz[] field to LibRaw interface only because it was a very small step (2 lines of code and 5 lines in documentation).