ppmdither

Updated: 16 December 2009
Table Of Contents

NAME

ppmdither - ordered dither for color images

SYNOPSIS

ppmdither [-dim=power] [-red=n] [-green=n] [-blue=n] [netpbmfile]

All options can be abbreviated to their shortest unique prefix. You may use two hyphens instead of one to designate an option. You may use either white space or an equals sign between an option name and its value.

DESCRIPTION

This program is part of Netpbm.

ppmdither reads a Netpbm image as input, and applies dithering to it to reduce the number of colors used down to the specified number of shades for each primary. It produces a PPM image as output.

The default number of shades is 5 red, 9 green, and 5 blue, for a total of 225 colors. To convert the image to a binary rgb format suitable for primitive color printers, use -red=2 -green=2 -blue=2.

You can do another kind of dither -- Floyd-Steinberg -- with pnmquant or pnmremap.

OPTIONS

In addition to the options common to all programs based on libnetpbm (most notably -quiet, see Common Options), ppmdither recognizes the following command line options:

-dim power: The size of the dithering matrix. The dithering matrix is a square whose dimension is a power of 2. power is that power of 2. The default is 4, for a 16 by 16 matrix.
-red=n: The number of red shades to be used, including black; minimum of 2.
Default is 5.
-green n: The number of green shades to be used, including black; minimum of 2.
Default is 9.
-blue n: The number of blue shades to be used, including black; minimum of 2.
Default is 5.