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RedHat 9 (Linux i386) - man page for pbmtopgm (redhat section 1)

pbmtopgm(1)			     General Commands Manual			      pbmtopgm(1)

       pbmtopgm - convert PBM image to PGM by averaging areas

       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  sur-
       rounding area is a rectangle of width by height pixels.

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

       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 (assum-
       ing 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, 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

					   03 Sep 2001				      pbmtopgm(1)

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