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1 perry 1 pgmnorm
2 !!!pgmnorm
3 NAME
4 SYNOPSIS
5 DESCRIPTION
6 OPTIONS
7 SEE ALSO
8 AUTHOR
9 ----
10 !!NAME
11
12
13 pgmnorm - normalize the contrast in a portable graymap
14 !!SYNOPSIS
15
16
17 __pgmnorm__ [[__-bpercent__ ''N'' | __-bvalue__
18 ''N''] [[__-wpercent__ ''N'' | __-wvalue__
19 ''N''] [[''pgmfile'']
20 !!DESCRIPTION
21
22
23 Reads a portable graymap as input. Normalizes the contrast
24 by forcing the lightest pixels to white, the darkest pixels
25 to black, and linearly rescaling the ones in between; and
26 produces a portable graymap as output.
27 !!OPTIONS
28
29
30 By default, the darkest 2 percent of all pixels are mapped
31 to black, and the lightest 1 percent are mapped to white.
32 You can override these percentages by using the
33 __-bpercent__ and __-wpercent__ flags, or you can
34 specify the exact pixel values to be mapped by using the
35 __-bvalue__ and __-wvalue__ flags. Appropriate numbers
36 for the flags can be gotten from the ''pgmhist'' tool. If
37 you just want to enhance the contrast, then choose values at
38 elbows in the histogram; e.g. if value 29 represents 3% of
39 the image but value 30 represents 20%, choose 30 for
40 ''bvalue''. If you want to lighten the image, then set
41 ''bvalue'' to 0 and just fiddle with ''wvalue'';
42 similarly, to darken the image, set ''wvalue'' to maxval
43 and play with ''bvalue''.
44
45
46 All flags can be abbreviated to their shortest unique
47 prefix.
48 !!SEE ALSO
49
50
51 pgmhist(1), ppmnorm(1), pgm(5)
52 !!AUTHOR
53
54
55 Partially based on the fbnorm filter in Michael Mauldin's
56
57
58 Copyright (C) 1989 by Jef Poskanzer.
59 ----
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