pbmtopgm(1) - man - phpman

pbmtopgm(1)                            General Commands Manual                           pbmtopgm(1)



NAME
       pbmtopgm - convert portable bitmap to portable graymap by averaging areas


SYNOPSIS
       pbmtopgm width height [pbmfile]


DESCRIPTION
       pbmtopgm  reads  a  portable  bitmap  as  input.  It outputs a portable graymap in which each
       pixel's gray level is the average 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 similar to a special case of pnmconvol.

       You may need a ppmsmooth 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.


SEE ALSO
       netpbm(1), pgmtopbm(1), pbm(5)


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  support‐
       ing documentation.  This software is provided "as is" without express or implied warranty.



                                             03 Sep 2001                                 pbmtopgm(1)