Convert a PNM file to a Sun rasterfile.
Convert a PNM image to a RAST image
pnmtorast path/to/input.pnm > path/to/output.rast
Force either `RT_STANDARD` or `RT_BYTE_ENCODED` form for the output
pnmtorast -standard|rle path/to/input.pnm > path/to/output.rast