Uses the colors found in the mapfile to create the colormap in the GIF file, instead of the colors from ppmfile. The mapfile can be any ppm file; all that matters is the colors in it. If the colors in ppmfile do not match those in mapfile , they are matched to a "best match". A (much) better result can be obtained by using the following filter in advance:
ppmquant -floyd -map mapfile
All flags can be abbreviated to their shortest unique prefix.
Copyright (C) 1989 by Jef Poskanzer.