Where does colormapping take place?

[N. Coesel]

Hello all,
I have the following problem. I need to be able to adjust gamma, 
brightness and contrast of a display which has no such controls (its 
on a framebuffer device using RGB565 Truecolor). This means the 
adjustment has to be done in software. Setting the gamma in the 
config file also doesn't work and xrandr is also unable to set gamma values.

So here is my idea: Patch Xorg. Somewhere in Xorg there is a 
translation from what is drawn on te window to the RGB565 values. The 
problems is that I really can't find where this translation takes 
place. I've located several places where the colormaps are defined 
and tried to alter the values but that has no influence at all. So my 
question is: where is the translation actually taking place for 
Truecolor displays?

Nico Coesel