[Openchrome-users] Brightness/contrast controls?

[Luc Verhaegen]

On Tue, May 01, 2007 at 03:09:28PM -0300, Andrei Formiga wrote:
> Hi,
> 
> I'm not sure this is adequate for this list, sorry. I want to change
> brightness and contrast levels globally for my display. Here's my
> case:
> 
> I have a computer with a UniChrome videoboard (windows says it's
> KM400/KN400, lspci says it's VT8378), and just yesterday I bought a
> LCD monitor (Samsung Syncmaster 740N) to replace my old CRT. But it's
> normally too bright and the colors get washed out and
> indistinguishable. On windows I solved this by going to the video
> board settings and tweaking with the gamma controls there; reducing
> gamma, brightness & contrast a bit I get an excellent image from the
> monitor, very crisp colors. The brightness & contrast controls from
> the windows driver are NOT the same as the brightness & contrast
> controls from the monitor. I tried tweaking the monitor settings and I
> cannot get the same result as with the driver's controls. Also,
> adjusting only gamma I can't get the same image quality.
> 
> Then I rebooted into Linux. Same problem with all the brightness and
> washed-out colors. First I tried adjusting gamma, to no avail; found
> out I was using the vesa driver that didn't support gamma, so I
> compiled the openchrome drivers, it works. I used xgamma and reduced
> the gamma a bit. It's an improvement, but I still can't distinguish
> some colors. So I need the brightness & contrast controls that are
> there on the windows driver.
> 
> I tried looking for a way to change this in X, to no avail. I looked
> at openchrome's source code, but could only find references to
> brightness and contrast in the context of Xv; I guess that's not what
> I want. Searching the web, I found that the linux nvidia drivers have
> these settings, and being that I used the driver to adjust the
> settings on windows, I thought about asking this here: is there a way
> to change brightness and contrast with the current openchrome drivers?
> If so, how? Thanks in advance for any help.
> 
xgamma only expose a limited control over the gamma curve. It at most 
allows you to specify seperate values for r,g,b, to which a curve then 
gets mapped, and the full 256x3 gamma curve then gets uploaded to the 
hardware.

A gui could be created to alter the actual gamma curve, but i doubt that 
such a thing currently exists for anything other than Twini's SiS 
driver (with twini's SiS specific extension).

Luc Verhaegen.
http://unichrome.sf.net/