[Digikam-users] Gamma on Linux

[Milan Knížek]

Leonardo Giordani píše v St 03. 02. 2010 v 16:22 +0100:
> Hi all,
> 
> I'm trying to understand the gamma tuning of Linux: I always read on
> Internet that we aim at gamma 2.2, but if I set Gamma 2.2 through
> xgamma, I get a way too bright monitor, I cannot even see black. The
> best value (without real calibration) is 1.0 (xgamma -gamma 1.0).

Your monitor has definitely native gamma around 2.4 - 2.5. Higher native
gamma results in darker mid-tones.

xgamma (or setting in /etc/X11/xorg.conf or the video driver tools like
nvidia-settings panel) tells X server to change the gamma of video card
LUT (look-up-table). Adjustments bigger then 1 make the mid-tones
lighter.

Additionally, there are tools (xcalib, dispwin) which can do finer
adjustments to the video card LUT then just the simple xgamma. However,
one needs to use a calibration device.

What you finally see on your screen is a result of monitor's native
gamma and any gamma adjustments to video card LUT. (Monitor gamma
divided by LUT gamma.)

> I'm a bit puzzled by this: what is the nominal gamma of my monitor (a
> Samsung SyncMaster, so a very common one)? If it is 2.2 why shall I
> set it to 1.0?

The various tools for gamma adjustments do not tell you what is the
visual gamma, but only what gamma adjustment is done to LUT.

regards,

Milan Knizek
knizek (dot) confy (at) volny (dot) cz
http://www.milan-knizek.net - About linux and photography (Czech
language only)