1Pamlevels User Manual(0) Pamlevels User Manual(0)
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6 pamlevels - effect a 'levels' transformation
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10 pamlevels -from1 from1 -to1 to1 -from2 from2 -to2 to2 [-from3 from3
11 -to3 to3] [-linear] [-fitbrightness] [pamfile]
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15 This program is part of Netpbm(1).
16 pamlevels reads a Netpbm image from pamfile or standard input, applies
18 a 'levels' transformation, and sends the result to standard output. It
19 finds a unique transformation that maps color from1 to to1, color from2
20 to to2, and-if -from3 and -to3 are supplied-color from3 to to3. Trans‐
21 formations based on two mappings are linear in light intensity and
22 those based on three mappings quadratic. The color-mapping options may
23 be shortened to -f1...-f3 and -t1...-t3.
24 Color values have the following format: color[:scale], where color is a
26 Netpbm color specification ⟨libppm.html#colorname⟩ and scale an
27 optional coefficient that is applied to the intensity (i.e. not gamma-
28 adjusted) of each RGB component of color.
29 When the transformation is linear (i.e. uses two mappings) and pre‐
31 serves zero (i.e. maps black to black), it corresponds to multiplica‐
32 tion of light intensity by a constant and preserves color integrity(1).
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37 In the examples below, \ denotes a line continuation:
38 To brighten an image by setting a darker white point- -f2 white:0.9 -t2
40 white in.ppm > out.ppm</pre>
41 To adjust the white point-
43 pamlevels -f1 black -t1 black\
44 -f2 rgbi:0.9/0.83/0.80 -t2 white in.ppm > out.ppm</pre>
45 To set a lighter black point-
47 -f2 white -t2 white in.ppm > out.ppm</pre>
48 To increase brightness by compression-
50 -f1 black -t1 black -f2 white -t2 white \
51 -f3 white:0.5 -t3 white:0.6 in.ppm > out.ppm</pre>
52 The latter tranformation is similar to gamma-correction.
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56 In addition to the options common to all programs based on libnetpbm
57 (most notably -quiet, see
58 Common Options ⟨index.html#commonoptions⟩ ), pamlevels recognizes the
59 following command line options:
60 -from1
64 -to1
66 -from2
68 -to2
70 -from3
72 -to3 These options define the mappings of input colors to output col‐
74 ors that anchor the transformation function. See DESCRIPTION
75 ⟨#description⟩ .
76 You must specify at least two of these pairs.
78 -linear
81 This option tells pamlevels to work with the intensity-linear
82 variation on PPM where the samples are proportional to light
83 intensity, rather than brightness (gamma-adjusted) as in true
84 PPM. The input must be of this form and the pamlevels makes the
85 output of this form.
86 Note that the numbers in a color specification like
88 rgbi:0.9/0.83/0.80 are brightness levels (gamma-adjusted)
89 regardless of the input and output format.
90 You cannot use this with -fitbrightness because that function is
92 not implemented.
93 -fitbrightness
96 This option selects a transformation which is not very useful -
97 it is linear or quadratic in brightness rather than light inten‐
98 sity of the pixels. There is no physical basis for doing it
99 this way and the result is normally undesirable.
100 Note that many tools other than Netpbm do the transformation
102 this way. One use for this option is simply to demonstrate the
103 poor result of this method.
104 One advantage of this transformation is that it is faster,
106 because the input and output image formats use brightness val‐
107 ues. The result is approximately correct.
108 You cannot use this with -linear because that function is not
110 implemented.
111
116 pnmnorm(1), pamrecolor(1), pnmgamma(1), pnm(1)
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120 This program was first submitted by Anton Shepelev
121 (anton.txt@gmail.com).
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125 pamlevels was new in Netpbm 10.83 (June 2018).
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128 This manual page was generated by the Netpbm tool 'makeman' from HTML
129 source. The master documentation is at
130 http://netpbm.sourceforge.net/doc/pamlevels.html
132netpbm documentation 13 June 2018 Pamlevels User Manual(0)