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  spe-
       cial case of pnmconvol.

       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  (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.

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


       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,  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.

netpbm documentation              05 Feb 2003          Pbmtopgm User Manual(0)

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