pbmreduce


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  reso-
       lution,  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 boustrophe-
       donic 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)
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