Convert a PNM image to a PostScript file. More information: https://netpbm.sourceforge.net/doc/pnmtops.html.
pnmtops path/to/file.pnm > path/to/file.ps
pnmtops -imagewidth imagewidth -imageheight imageheight path/to/file.pnm > path/to/file.ps
pnmtops -width width -height height path/to/file.pnm > path/to/file.ps