Output
luminance is approximately equal to the input value (in the range 0??“1) raised to a
power of 2.2 (of course, the monitor??™s brightness and contrast controls will also
come into play, offsetting and amplifying this value). The exponent in this transfer
function is called the gamma value.
Non-CRT monitors such as LCD panels, plasma displays, and projectors all process
the input to produce roughly the same gamma curve as a CRT. In order to compensate
for the this curve, video cameras are designed with a gamma of approximately
0.4; most digital images (such as those from digital cameras) are also adjusted to
assume a nonlinear output curve.
sRGB assumes an effective monitor gamma of 2.2. If your monitor??™s gamma value is
incorrect, images will not be displayed as accurately as possible; gamma correction
can be applied to the X server??™s output to compensate.
The XFREE86-VIDMODE Extension enables the dynamic adjustment of the gamma
correction settings. As the name implies, this is an extension that originated with
XFree86 and has been inherited by the X.org project; since this is an extension to the
X11 protocol, not all servers will be equipped with it.
9.3
9.3 Gamma 139
A basic client program for displaying and adjusting the X server??™s gamma value is
xgamma.
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