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 -from1
57 -to1
59 -from2
61 -to2
63 -from3
65 -to3 These options define the mappings of input colors to output col‐
67 ors that anchor the transformation function. See DESCRIPTION
68 ⟨#description⟩ .
69 You must specify at least two of these pairs.
71 -linear
74 This option tells pamlevels to work with the intensity-linear
75 variation on PPM where the samples are proportional to light
76 intensity, rather than brightness (gamma-adjusted) as in true
77 PPM. The input must be of this form and the pamlevels makes the
78 output of this form.
79 Note that the numbers in a color specification like
81 rgbi:0.9/0.83/0.80 are brightness levels (gamma-adjusted)
82 regardless of the input and output format.
83 You cannot use this with -fitbrightness because that function is
85 not implemented.
86 -fitbrightness
89 This option selects a transformation which is not very useful -
90 it is linear or quadratic in brightness rather than light inten‐
91 sity of the pixels. There is no physical basis for doing it
92 this way and the result is normally undesirable.
93 Note that many tools other than Netpbm do the transformation
95 this way. One use for this option is simply to demonstrate the
96 poor result of this method.
97 One advantage of this transformation is that it is faster,
99 because the input and output image formats use brightness val‐
100 ues. The result is approximately correct.
101 You cannot use this with -linear because that function is not
103 implemented.
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109 pnmnorm(1), pamrecolor(1), pnmgamma(1), pnm(1)
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113 This program was first submitted by Anton Shepelev
114 (anton.txt@gmail.com).
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118 pamlevels was new in Netpbm 10.83 (June 2018).
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121 This manual page was generated by the Netpbm tool 'makeman' from HTML
122 source. The master documentation is at
123 http://netpbm.sourceforge.net/doc/pamlevels.html
125netpbm documentation 13 June 2018 Pamlevels User Manual(0)