[lug] Adjusting color balance

[D. Stimits]

Elyse M. Grasso wrote:

> Is there a way to globally adjust the color balance of a monitor in X 
> windows,
> instead of having to adjust each individual image  and/or application? 
> For
> some reason reds are weak on my laptop when it is booted into Linux. 
> This is
> annoying when viewing DVDs and images, and doing color layouts.
>
> It might just be a pallete selection problem , but I'm not sure how to 
> attack
> that either.
>
>  (I'm running KRUD 9 and KDE).
>
> Windows seems less unbalanced, on the rare occasions when I boot into it.
>
> Are there good sample color wheels or other standard images I could 
> use when
> trying to diagnose and tweak things?


I think the answer will be dependent upon the particular video card and 
drivers. I say this because I expect it to be an XF86Config option that 
is implemented only if the driver authors decided to add it. The option 
is "gamma". Gamma correction can come in several flavors, one being just 
plain old gamma that is uniform across all colors; optionally some 
driver implementors might make available a separate gamma for each of 
the primary colors.

An uncorrected gamma is 1.0; a gamma to brighten intermediate intensity 
colors is any gamma over 1.0. Gamma is designed to correct for the 
difference between monitor brightness at various intensities over a 
range of full dark to full light, having the most effect between full 
dark and full light, and gradually tapering off to have no effect on 
pure dark or pure light. If you used something to simply boost 
brightness across all intensities, then lighter colors would bleach out 
and lose contrast; if you darkened across the whole range of 
intensities, then the darker colors would go completely black and no 
contrast would be visible. Gamma does not bleach out whiter colors, nor 
does it darken darker colors into oblivion. I'd suggest finding the X11 
driver docs for your video card driver, and hunting for gamma.

On the other hand, if you give your video card type info to the LUG 
list, perhaps someone here already knows what gamma settings are 
available, and can tell you exactly what line to add to XF86config.

D. Stimits, stimits AT comcast DOT net