pbmreduce(1)

NAME

   pbmreduce - read a portable bitmap and reduce it N times

SYNOPSIS

   pbmreduce [-floyd|-fs|-threshold ] [-value val] N [pbmfile]

DESCRIPTION

   Reads  a  portable  bitmap  as input.  Reduces it by a factor of N, and
   produces a portable bitmap as output.

   pbmreduce duplicates a lot of the functionality of pgmtopbm; you  could
   do something like pnmscale | pgmtopbm, but pbmreduce is a lot faster.

   pbmreduce  can be used to "re-halftone" an image.  Let's say you have a
   scanner that only produces black&white, not grayscale, and  it  does  a
   terrible  job  of  halftoning (most b&w scanners fit this description).
   One way to fix the halftoning  is  to  scan  at  the  highest  possible
   resolution,  say  300  dpi,  and then reduce by a factor of three or so
   using pbmreduce.  You can even correct the brightness of an  image,  by
   using the -value flag.

OPTIONS

   By   default,   the   halftoning   after  the  reduction  is  done  via
   boustrophedonic   Floyd-Steinberg   error   diffusion;   however,   the
   -threshold flag can be used to specify simple thresholding.  This gives
   better results when reducing line drawings.

   The -value flag alters the thresholding value  for  all  quantizations.
   It  should  be  a  real number between 0 and 1.  Above 0.5 means darker
   images; below 0.5 means lighter.

   All flags can be abbreviated to their shortest unique prefix.

SEE ALSO

   pnmenlarge(1), pnmscale(1), pgmtopbm(1), pbm(5)

AUTHOR

   Copyright (C) 1988 by Jef Poskanzer.

                            02 August 1989                    pbmreduce(1)

---

Free and Open Source Software