pgmtopbm - convert a PGM image to PBM
[-floyd | -fs | -threshold | -hilbert | -dither8 | -d8 | -cluster3 | -c3 | -cluster4 | -c4 | -cluster8 | -c8]
This program is part of Netpbm(1).
This program is obsolete since Netpbm 10.23 (July 2004). Use pamditherbw(1) to do what this program used to do.
pgmtopbm never was the simple converter it appeared to be. It was a dithering program. Unfortunately, it didn't do the dithering properly because it treated the PGM input samples as if they were directly proportional to light intensity, but they are actually gamma-adjusted.
pamditherbw is backward compatible with pgmtopbm except that it
So use the manual for pamditherbw for pgmtopbm, except ignore anything that says it was added after Netpbm Release 10.23 and ignore any options that are not shown in the synopsis above.
If you just want to convert a PGM image with maxval 1 to PBM, use pamtopnm(1)