ppmtorgb3 - separate a portable pixmap into three portable graymaps
Reads a portable pixmap as input. Writes three portable graymaps as output, one each for red, green, and blue.
The output filenames are constructed by taking the input filename, stripping off any extension, and appending ".red", ".grn", and ".blu". For example, separating lenna.ppm would result in lenna.red, lenna.grn, and lenna.blu. If the input comes from stdin, the names are noname.red, noname.grn, and noname.blu.
Copyright (C) 1991 by Jef Poskanzer.