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 [-randomseed=integer]
11       [pbmfile]
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13       You can abbreviate any option to its shortest unique prefix.
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DESCRIPTION

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

36       -threshold
37              By  default,  pbmreduce  does the halftoning after the reduction
38              via boustrophedonic Floyd-Steinberg  error  diffusion;  however,
39              you  can  use  this option to specify simple thresholding.  This
40              gives better results when reducing line drawings.
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43       -value
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45              This option alters the thresholding value for all quantizations.
46              It  should  be  a  real number between 0 and 1.  Above 0.5 means
47              darker images; below 0.5 means lighter.
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50       -randomseed=integer
51              This is the seed for the random number generator  that  controls
52              the halftoning.
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54              Use  this  to  ensure you get the same image on separate invoca‐
55              tions.
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57              This option was new in Netpbm 10.75 (June 2016).
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SEE ALSO

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

68       Copyright (C) 1988 by Jef Poskanzer.
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DOCUMENT SOURCE

71       This manual page was generated by the Netpbm tool 'makeman'  from  HTML
72       source.  The master documentation is at
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74              http://netpbm.sourceforge.net/doc/pbmreduce.html
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76netpbm documentation             13 April 2016        Pbmreduce User Manual(0)