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 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 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.

OPTIONS

       There are no command line options defined specifically for pbmtopgm, but it recognizes the
       options common to all programs based on libnetpbm (See
        Common Options ⟨index.html#commonoptions⟩ .)

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, 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
       warranty.

DOCUMENT SOURCE

       This  manual page was generated by the Netpbm tool 'makeman' from HTML source.  The master
       documentation is at

              http://netpbm.sourceforge.net/doc/pbmtopgm.html