Possible bug in display profiles auto-generated from EDID: 'chad' tag converts from PCS to device

[Florian Höch <lists+gnome-color-manager hoech org>]

Hi,

it seems the 'chad' tag autogenerated by GCM from EDID may not be 
according to the ICC v4 spec:

"This tag, which must be invertible, converts an XYZ colour, measured at 
a device's specific illumination conditions, to an XYZ colour in the PCS 
illumination conditions after complete adaptation."

So, the inverted matrix should do the opposite.

This is not the case with the profile I looked at. When I multiply the 
inverted matrix with D50 XYZ numbers, which should yield the device 
illuminant (CCT around 6460K, I know it from looking at the EDID), I get 
a far too 'warm' result (CCT around 4408K). Not inverting the matrix 
yields the correct values.

I'm not sure if this is a GCM or LCMS bug. I can provide the ICC profile 
in question (and a few 'reference' profiles from other profiling 
solutions which seem to have correct 'chad' tags) if needed.

The GCM version I used is from Fedora 15 (3.0.0-3.fc15). I skimmed the 
commit messages of the git repo to see if it's maybe already fixed 
upstream, but couldn't find anything.

Regards
--
Florian Höch