This program is part of Netpbm.

pgmtopgm simply copies a PGM image from Standard Input to Standard
Output. This may seem an unnecessary duplication of cat, but remember
that a PGM program can read a PBM image as if it were PGM. So pgm-
topgm can read either a PBM or PGM image and produce a PGM image as

Even that is of limited usefulness because of the fact that almost any
program to which you would feed the resulting PGM image could also
just take the original image directly. However, sometimes you really
need a true PGM image.

When you know you have a PBM image and want a PGM image, pbmtopgm is a
more general way to do that conversion.

ppmtoppm, pamtopam, pamtopnm, pbmtopgm, pbm, pgm,

This program was added to Netpbm in Release 10.9 (September 2002).

netpbm documentation September 2002 Pgmtopgm User Manual(0)