centos man page for pnm

The PNM Format(5)						File Formats Manual						 The PNM Format(5)

NAME
       pnm - Netpbm superformat

DESCRIPTION
       The PNM format is just an abstraction of the PBM, PGM, and PPM formats.	I.e. the name 'PNM' refers collectively to PBM, PGM, and PPM.

       The  name  'PNM'  is  an acronym derived from 'Portable Any Map.' This derivation makes more sense if you consider it in the context of the
       other Netpbm format names: PBM, PGM, and PPM.

       The more general term 'Netpbm format' refers to the PNM formats plus PAM.

       PNM is principally used with Netpbm(1)

       Note that besides being names of formats, PBM, PGM, PPM, and PNM are also classes of programs.  A PNM program can take  PBM,  PGM,  or  PPM
       input.	That's	nothing  special -- a PPM program can too.  But a PNM program can often produce multiple output formats as well, and a PNM
       program can see the difference between PBM, PGM, and PPM input and respond to each differently whereas a PPM program sees everything as	if
       it were PPM.  This is discussed more in the description of the netpbm programs (1)

       'pnm' also appears in the names of the most general Netpbmlibraryroutines(1) , some of which aren't even related to the PNM format.

SEE ALSO
       ppm(1) , pgm(1) , pbm(1) , pam(1) , programsthatprocessPNM(1) , libnetpbm(1)

netpbm documentation						  03 October 2003						 The PNM Format(5)