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)