share a common colormap
[-ext extension] ncolors ppmfile...
This program is part of Netpbm.
ppmquantall takes a bunch of PPM images as input, chooses ncolors col-
ors to best represent all of the images, maps the existing colors to
the new ones, and overwrites the input files with the new quantized
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 PPMs that you want
to display on the screen all at the same time. Your screen can only
display 256 different colors, but the PPMs have a total of a thousand
or so different colors. For a single PPM you solve this problem with
pnmquant; ppmquantall solves it for multiple PPMs. All it does is
concatenate them together into one big PPM, run pnmquant on that, and
then split it up into little PPMs again.
(Note that another way to solve this problem is to pre-select a set of
colors and then use pnmremap to separately quantize each PPM to that
pnmquant, pnmremap, pnmcolormap, ppm
Copyright (C) 1991 by Jef Poskanzer.
netpbm documentation 27 July 1990 Ppmquantall User Manual(0)