1Pbmreduce User Manual(0)                              Pbmreduce User Manual(0)
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NAME

6       pbmreduce - read a PBM image and reduce it N times
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SYNOPSIS

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

14       This program is part of Netpbm(1).
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16       pbmreduce  reads  a PBM image as input and reduces it by a factor of N,
17       producing a PBM image as output.
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19       pbmreduce duplicates a lot of the  functionality  of  pamditherbw;  you
20       could  do something like pamscale | pamditherbw, but pbmreduce is a lot
21       faster.
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23       You can use pbmreduce to 're-halftone' an image.  Let's say you have  a
24       scanner  that  only  produces black&white, not grayscale, and it does a
25       terrible job of halftoning (most b&w scanners  fit  this  description).
26       One  way to fix the halftoning is to scan at the highest possible reso‐
27       lution, say 300 dpi, and then reduce by a factor of three or  so  using
28       pbmreduce.   You  can even correct the brightness of an image, by using
29       the -value option.
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OPTIONS

33       You can abbreviate any option to its shortest unique prefix.
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35       By default, pbmreduce does the halftoning after the reduction via bous‐
36       trophedonic  Floyd-Steinberg  error diffusion; however, you can use the
37       -threshold option to specify simple thresholding.   This  gives  better
38       results when reducing line drawings.
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40       The  -value option alters the thresholding value for all quantizations.
41       It should be a real number between 0 and 1.   Above  0.5  means  darker
42       images; below 0.5 means lighter.
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SEE ALSO

46       pamenlarge(1), pamscale(1), pamditherbw(1), pbm(1)
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AUTHOR

50       Copyright (C) 1988 by Jef Poskanzer.
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54netpbm documentation            02 August 1989        Pbmreduce User Manual(0)