NAME

       pbmtopgm - convert portable bitmap to portable graymap 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, provided that the above copyright notice appear in all copies and that
       both that copyright notice and this permission notice appear in supporting documentation.  This  software
       is provided "as is" without express or implied warranty.

                                                   03 Sep 2001                                       pbmtopgm(1)