1Pbmreduce User Manual(0)                              Pbmreduce User Manual(0)
2
3
4

NAME

6       pbmreduce - read a PBM image and reduce it N times
7
8

SYNOPSIS

10       pbmreduce  [-floyd|-fs|-threshold] [-value val] [-randomseed=integer] N
11       [pbmfile]
12
13       You can abbreviate any option to its shortest unique prefix.
14
15

DESCRIPTION

17       This program is part of Netpbm(1).
18
19       pbmreduce reads a PBM image as input and reduces it by a factor  of  N,
20       producing a PBM image as output.
21
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.
25
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.
33
34

OPTIONS

36       In  addition  to  the options common to all programs based on libnetpbm
37       (most notably -quiet, see
38        Common Options ⟨index.html#commonoptions⟩ ), pbmreduce recognizes  the
39       following command line options:
40
41
42
43
44       -threshold
45              By  default,  pbmreduce  does the halftoning after the reduction
46              via boustrophedonic Floyd-Steinberg  error  diffusion;  however,
47              you  can  use  this option to specify simple thresholding.  This
48              gives better results when reducing line drawings.
49
50
51       -floyd, -fs
52              Specify the Floyd-Steinberg error diffusion method.  This is the
53              default.
54
55
56       -value
57
58              This option alters the thresholding value for all quantizations.
59              It should be a real number between 0 and  1.   Above  0.5  means
60              darker images; below 0.5 means lighter.
61
62
63       -randomseed=integer
64              This  is  the seed for the random number generator that controls
65              the halftoning.
66
67              Use this to ensure you get the same image  on  separate  invoca‐
68              tions.
69
70              This option was new in Netpbm 10.75 (June 2016).
71
72
73
74
75

SEE ALSO

77       pamenlarge(1), pamscale(1), pamditherbw(1), pbm(1)
78
79

AUTHOR

81       Copyright (C) 1988 by Jef Poskanzer.
82

DOCUMENT SOURCE

84       This  manual  page was generated by the Netpbm tool 'makeman' from HTML
85       source.  The master documentation is at
86
87              http://netpbm.sourceforge.net/doc/pbmreduce.html
88
89netpbm documentation             13 April 2016        Pbmreduce User Manual(0)