gammaramp - defines a color map ramp for gamma correction
void gammaramp(r, g, b)
short r, g, b
r expects an array of 256 elements. Each element contains a setting
for the red electron gun.
g expects an array of 256 elements. Each element contains a setting
for the green electron gun.
b expects an array of 256 elements. Each element contains a setting
for the blue electron gun.
gammaramp supplies a level of indirection for all color map and RGB
values. For example, before the system would turn on the red gun to
setting 238, the system looks in a table at location 238 and uses the
value it finds there instead of 238.
Thus, you can use this table to provide gamma correction, to equalize
monitors with different color characteristics, or to modify the color
warmth of the monitor. The default setting has r[i] = g[i] = b[i] = i.
(So at location 238 of the red, green, and blue tables, you find the
When the system is in RGB mode and draws an object, the system writes the
actual red, green, and blue values to the bitplanes not the indirect
values. However, the values that you see when the system draws the
bitmap to the screen are the indirect values: r[red], g[green], b[blue]
(where r,g,b are the arrays last specified by gammaramp).
Similarly, when the system is in color map mode and draws an object, the
system knows that the true color of the object may be color i, but to
determine the displayed color, the system finds the red, green, and blue
values of color i and displays color i as r[red], g[green], b[blue].
color, cmode, mapcolor, RGBcolor, gamma(6D)
This routine is available only in immediate mode.
On the IRIS-4D G, gamma correction in RGB mode uses the top 256 entries
of the colormap.
gammaramp should not be used in new developement. The X server
compensates for gamma in colors used by X clients. gammaramp will bypass
this. Use gammaramp with caution or a sense of humor.
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