Provided by: netpbm_10.0-12.2_i386 bug

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)