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Gamma
Gamma Correction
(Term of computer graphics)
Most computer and television monitors exhibit a response
function that approximates a simple power law, and the
exponent is called the monitor's gamma (γ).
This means that, given a input signal voltage range between 0
and 100% U for a luminance of 0 - 1,
if the monitor receives 50% of
that voltage for a specific point, it will display
a luminance of
L = 0.5*U γ
at that point.
Typical displays have gamma values between 1.5 and 3.0
The correct display of
images, whether computer-generated or captured,
requires compensation for the system's gamma response.
This gamma correction
can be done by the graphics hardware of by software.
Some operating systems allready apply a partial correction,
bringing the effective system gamma eg. to 1.8 or 1.4.
The Radiance software expects the system variable "DISPLAY_GAMMA" to
hold the value of the monitor gamma, so it can apply
the appropriate corrections when displaying images.
If no system gamma is given, a value of 2.2 is assumed.
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