pnmquant
Reduce color count in PNM images
TLDR
Reduce colors
$ pnmquant [256] [input.pnm] > [output.pnm]
Use median-cut algorithm$ pnmquant -center [16] [input.pnm] > [output.pnm]
Spread error (dithering)$ pnmquant -fs [256] [input.pnm] > [output.pnm]
SYNOPSIS
pnmquant [options] ncolors [file]
DESCRIPTION
pnmquant reduces the number of colors in a PNM image to a specified count using the median-cut color quantization algorithm. This is useful for preparing images for formats with limited color palettes or for reducing file size.
The -fs option enables Floyd-Steinberg dithering to simulate more colors by distributing quantization error to neighboring pixels. The -mapfile option allows quantizing to a pre-defined color palette from another image. Part of the Netpbm toolkit; wrapper around pnmcolormap and pnmremap.
PARAMETERS
ncolors
Target number of colors.-fs
Floyd-Steinberg dithering.-center
Center box color selection.-spreadbrightness
Spread brightness.-mapfile file
Use colormap from file.