Pbmreduce User Manual(0)                              Pbmreduce User Manual(0)


       pbmreduce - read a PBM image and reduce it N times


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

       You can abbreviate any option to its shortest unique prefix.


       This program is part of Netpbm(1).

       pbmreduce  reads  a PBM image as input and reduces it by a factor of N,
       producing a PBM image as output.

       pbmreduce duplicates a lot of the  functionality  of  pamditherbw;  you
       could  do something like pamscale | pamditherbw, but pbmreduce is a lot

       You can use pbmreduce 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 option.


       By default, pbmreduce does the halftoning after the reduction via bous-
       trophedonic  Floyd-Steinberg  error diffusion; however, you can use the
       -threshold option to specify simple thresholding.   This  gives  better
       results when reducing line drawings.

       The  -value option 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.


       pnmenlarge(1), pamscale(1), pamditherbw(1), pbm(1)


       Copyright (C) 1988 by Jef Poskanzer.

netpbm documentation            02 August 1989        Pbmreduce User Manual(0)

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