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



NAME
       pbmtopgm - convert PBM image to PGM by averaging areas


SYNOPSIS
       pbmtopgm width height [pbmfile]


DESCRIPTION
       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.


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


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,  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)