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)