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





       Table Of Contents


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

       In other words, this is a convolution.  pbmtopgm is sim-
       ilar to a special 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 lev-
       els.   So  unless  your  convolution rectangle is bigger
       than one pixel, you're not gaining anything with a  pbm-
       topgm 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 with-
       out fee is hereby granted, provided that the above copy-
       right  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 warranty.



netpbm documentation      05 Feb 2003   Pbmtopgm User Manual(0)
