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Pbmtopgm User Manual(0) 						  Pbmtopgm User Manual(0)

       pbmtopgm - convert PBM image to PGM by averaging areas

       pbmtopgm width height [pbmfile]

       This program is part of Netpbm(1)

       pbmtopgm  reads	a  PBM image as input.	It outputs a PGM image in which each pixel's gray
       level is the average of 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 pnmcon-

       You may need a pnmsmooth 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 minimum and maximum gray levels.  So unless your  convolution  rectangle  is
       bigger than one pixel, you're not gaining anything with a pbmtopgm step.

       The  opposite  transformation  (which  would  turn  a  PGM  into a PBM) is dithering.  See

       pamditherbw(1) , pnmconvol(1) , pbm(1) , pgm(1)

       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

netpbm documentation			   05 Feb 2003			  Pbmtopgm User Manual(0)
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