gammaramp(3G)                                                    gammaramp(3G)


NAME
     gammaramp - defines a color map ramp for gamma correction

C SPECIFICATION
     void gammaramp(r, g, b)
     short r[256], g[256], b[256]

PARAMETERS
     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.

DESCRIPTION
     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
     value 238.)

     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].

SEE ALSO
     color, cmode, mapcolor, RGBcolor, gamma(6D)

NOTES
     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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