fill_dither(3G)

NAME

fill_dither − set color value for filled areas on raster devices.

SYNOPSIS

C Syntax:

void fill_dither ( fildes, colors );
int fildes, colors;

FORTRAN77 Syntax:

subroutine fill_dither ( fildes, colors )
integer*4 fildes, colors

Pascal Syntax:

procedure fill_dither ( fildes, colors:integer );

DESCRIPTION

Input Parameters

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

colors Number of colors to be searched for and placed in the dither cell. Only 1, 2, 4, 8 and 16 are allowed. Devices may limit the number of options implemented for this parameter, depending on device capabilities.

Discussion

Dithering is a method of generating more fill colors than are available in the color table. It uses the human eye’s ability to integrate or blend closely-spaced small pinpoints of color called pixels, each of which can be set to certain predefined colors, into an average color over the entire dither cell. Each dither cell is composed of 16 (red, blue, green) pixel triples where each triple can be set to certain combinations of color and relative intensity in order to produce the desired dither cell color. For a more extensive explanation of how dithering is achieved, see Starbase Graphics Techniques.

See fill_color for an in-depth discussion of how fill_color and fill_dither are interrelated.

DEFAULTS

Device-dependent dithering for colors specified by RGB values (via fill_color), but not for colors selected by index (fill_color_index).

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