ppmquantall – run ppmquant on a bunch of files all at once, so they
share a common colormap
ppmquantall [-ext extension] ncolors ppmfile …
Takes a bunch of portable pixmap as input. Chooses ncolors colors to
best represent all of the images, maps the existing colors to the new
ones, and overwrites the input files with the new quantized versions.
If you don’t want to overwrite your input files, use the -ext option.
The output files are then named the same as the input files, plus a
period and the extension text you specify.
Verbose explanation: Let’s say you’ve got a dozen pixmaps that you want
to display on the screen all at the same time. Your screen can only
display 256 different colors, but the pixmaps have a total of a thou‐
sand or so different colors. For a single pixmap you solve this prob‐
lem with ppmquant; this script solves it for multiple pixmaps. All it
does is concatenate them together into one big pixmap, run ppmquant on
that, and then split it up into little pixmaps again.
(Note that another way to solve this problem is to pre-select a set of
colors and then use ppmquant’s -map option to separately quantize each
pixmap to that set.)
Copyright (C) 1991 by Jef Poskanzer.
27 July 1990 ppmquantall