rasttopnm - convert a Sun rasterfile into a portable anymap
       rasttopnm [rastfile]
       Reads a Sun rasterfile as input.  Produces a portable anymap as output.
       The type of the output file depends on the input file - if it’s black &
       white, a pbm file is written, else if it’s grayscale a pgm file, else a
       ppm file.  The program tells you which type it is writing.
       pnmtorast(1), pnm(5)
       Copyright (C) 1989, 1991 by Jef Poskanzer.
                                13 January 1991                   rasttopnm(1)