| Gamma Correction.
A gimg compensates the non-linear response of an image to display.
The option -gmid specifies the type of gamma correction while the
option -gamma specifies the intensity of the correction. Two types of gamma
corrections are available. The option -gmid has two values: 0 and
1. A value 0 of the option -gmid specifies a type 0 gamma correction.
It defines a regular gamma correction function g(v,r) = 255 * pow(v/255,
r) for a CRT monitor, where v is the value of a pixel and r is the intensity
of gamma correction. A value 1 of the option -gmid specifies a type
1 gamma correction. It defines a correction function f(v) such that f(v,r)
= g(v,r) for 0 <= v <= 127 and f(v,r) = g(255-v,r) for 128 <=
v <= 255. A type 1 gamma correction is suitable to correctly displaying
an image scanned from a film. The option -gamma defines the intensity
of gamma correction. An intensity value of one is a NULL gamma correction,
and an intensity value less or greater than one may either reduce or increase
gamma distortion depending on the true image value distribution.
The following two examples show the differences of the same digital
elevation image displayed without and with gamma correction. A typical
type one gamma correction value for a CRT monitor is 0.45.
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