redhat man page for pbmtopgm

pbmtopgm(1)						      General Commands Manual						       pbmtopgm(1)

NAME
       pbmtopgm - convert PBM image to PGM by averaging areas

SYNOPSIS
       pbmtopgm width height [pbmfile]

DESCRIPTION
       pbmtopgm  reads	a portable bitmap as input.  It outputs a portable graymap in which each pixel's gray level is the average the surrounding
       black and white input pixels.  The surrounding area is a rectangle of width by height pixels.

       In other words, this is a convolution.  pbmtopgm is similar to a special case of pnmconvol.

       You may need a ppmsmooth step after pbmtopgm.

       pbmtopgm has the effect of anti-aliasing bitmaps which contain distinct line features.

       pbmtopgm works best with odd sample width and heights.

       You don't need pbmtopgm just to use a PGM program on a PBM image.  Any PGM program (assuming it uses the Netpbm libraries to read  the  PGM
       input)  takes  PBM  input as if it were PGM, with only the mininum and maximum gray levels.  So unless your convolution rectangle is bigger
       than one pixel, you're not gaining anything with a pbmtopgm step.

SEE ALSO
       netpbm(1), pgmtopbm(1), pbm(5)

AUTHOR
       Copyright (C) 1990 by Angus Duggan Copyright (C) 1989 by Jef Poskanzer.

       Permission to use, copy, modify, and distribute this software and its documentation for any purpose and without fee is hereby granted, pro-
       vided  that  the  above copyright notice appear in all copies and that both that copyright notice and this permission notice appear in sup-
       porting documentation.  This software is provided "as is" without express or implied warranty.

								    03 Sep 2001 						       pbmtopgm(1)