first cs depend case: brighness,contrast

[Casper Boemann]

Hi

I have indentified that the brightness contrast filter assumes rgb (or at 
least liniar tristimulas values).

This is naturally wrong and the question is how to solve it. I have two 
suggestions:

1:
for each pixel {
   cs->adjustbrightness(pixel, level);
}


2:
for each pixel {
  cs->setBrightness(pixel, (cs->getBrightness(pixel) * level);
}

#1 is simpler to use. Probably is faster and more accurate. But we run the 
risk of bloating the colorspaces, with many specific functions

#2 is more complex to use, but by using simpler functions we might be able to 
reuse them in another context.

What do you think, or do you have other alternatives?
-- 
best regards / venlig hilsen
Casper Boemann