pbmtopgm(1)                 General Commands Manual                pbmtopgm(1)

       pbmtopgm  -  convert  portable  bitmap to portable graymap by averaging

       pbmtopgm width height [pbmfile]

       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 spe-
       cial 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.

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

       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)
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