ppmquant
Reduce PPM image color count
TLDR
Reduce to N colors
$ ppmquant [256] [input.ppm] > [output.ppm]
Reduce to 16 colors$ ppmquant [16] [input.ppm] > [output.ppm]
With Floyd-Steinberg dithering$ ppmquant -fs [256] [input.ppm] > [output.ppm]
Use existing colormap$ ppmquant -map [palette.ppm] [input.ppm] > [output.ppm]
SYNOPSIS
ppmquant [options] ncolors [ppmfile]
DESCRIPTION
ppmquant reduces the number of colors in a PPM image using median-cut quantization. Essential for creating GIF images or reducing file size.
Superseded by pnmquant in modern Netpbm.
PARAMETERS
ncolors
Maximum number of colors.-fs
Floyd-Steinberg dithering.-map file
Use colormap from file.-spreadbrightness
Spread by brightness.-spreadluminosity
Spread by luminosity.
EXAMPLES
$ # Reduce to 256 colors
ppmquant 256 photo.ppm > reduced.ppm
# 16 colors with dithering
ppmquant -fs 16 image.ppm > dithered.ppm
# Use web-safe palette
ppmquant -map websafe.ppm image.ppm > websafe.ppm
# Convert for GIF
ppmquant 256 image.ppm | ppmtogif > image.gif
ppmquant 256 photo.ppm > reduced.ppm
# 16 colors with dithering
ppmquant -fs 16 image.ppm > dithered.ppm
# Use web-safe palette
ppmquant -map websafe.ppm image.ppm > websafe.ppm
# Convert for GIF
ppmquant 256 image.ppm | ppmtogif > image.gif
CAVEATS
Use pnmquant for new work. Dithering can increase file size. Part of Netpbm.
HISTORY
ppmquant is part of Netpbm by Jef Poskanzer, implementing the median-cut color quantization algorithm by Paul Heckbert.
SEE ALSO
pnmquant(1), pnmcolormap(1), ppmtogif(1), netpbm(1)