rgb_to_index(3G)

NAME

rgb_to_index − find the index of the closest color in the color map

SYNOPSIS

C Syntax:

int rgb_to_index ( fildes, red, green, blue )
int fildes;
float red, green, blue;

FORTRAN77 Syntax:

integer*4 function rgb_to_index ( fildes, red, green, blue )
integer*4 fildes
real red, green, blue

Pascal Syntax:

function rgb_to_index ( fildes:integer; red, green,
blue:real ):integer;

DESCRIPTION

Input Parameters

fildes Integer file descriptor returned by gopen when an I/O path to a graphics device is opened.

red, green, blue
Color values (in the range of 0.0 to 1.0) of the desired color.

Discussion

This call searches the color table for the closest color to (red, green, blue) and returns its index. The distance between colors is defined by the Euclidean metric — see the "Color" Chapter of the Starbase Graphics Techniques manual for details.

If the color map or double-buffer mode is modified, previously returned indices may be invalidated.

For grayscale devices, the (red, green, blue) values will be transformed to a grayscale intensity using the formula:

I = 0.30 × red + 0.59 × green + 0.11 × blue

before the color table is searched.

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