ppmtomap - create a map of all colors in a PPM image
This program is part of Netpbm(1).
This program exists only for backward compatibility.
Use pnmcolormap, which replaced it in January 2002.
One trivial difference between ppmtomap and pnmcolormap all is that if the input is PBM or PGM, ppmtomap would produce PPM output, whereas pnmcolormap all produces the same kind of output as the input. This should not be very noticeable, though, as PBM and PGM images are usually usable anywhere a PPM image is.