[Openicc] Changing the display whitepoint using the VCGT

[Richard Hughes]

Dear list,

My Dell mini display is very bluish by default (5000K whites), but
when I calibrate this using argyll and a hardware calibration device
the new profile sets a white temperature of 5700K and the display
looks a lot more pleasant. A very blue native white is also a problem
in some macbooks, and nearly all thinkpads.

I can easily create an RGB generated space using the EDID chromacity
co-ordinates and the EDID gamma, and gnome-color-manager has been
doing that for a few releases now. I'm wondering if it's sane to also
adjust the whitepoint using the VCGT feature.

I've been playing about with cmsAdaptToIlluminant and using the VCGT
which obviously does a linear conversion of white temperature, which
seems to work fairly well. I've noticed that argyll-generated profiles
seem to smooth to the maximum value a the top of the VCGT table and I
wondered if that was a result of manual tweaking to ensure that
255,255,255 == display-white or may just be a peculiarity of my
display.

I guess the real question is whether trying-to-be-helpful session
software should try to change the whitepoint of a display to anything
other than native or whether the VCGT table should just be left
unmolested.

Advice very welcome,

Thanks.

Richard