1Pamlevels User Manual(0) Pamlevels User Manual(0)
2
6 pamlevels - effect a 'levels' transformation
7
10 pamlevels -from1 from1 -to1 to1 -from2 from2 -to2 to2 [-from3 from3
11 -to3 to3] [-linear] [-fitbrightness] [pamfile]
12
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 op‐
27 tional coefficient that is applied to the intensity (i.e. not gamma-ad‐
28 justed) 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).
33
37 In the examples below, \ denotes a line continuation:
38 To brighten an image by setting a darker white point-
40 pamlevels -f1 black -t1 black \
41 -f2 white:0.9 -t2 white in.ppm > out.ppm
42 To adjust the white point-
45 pamlevels -f1 black -t1 black \
46 -f2 rgbi:0.9/0.83/0.80 -t2 white in.ppm > out.ppm
47 To set a lighter black point-
50 pamlevels -f1 white:0.06 -t1 black \
51 -f2 white -t2 white in.ppm > out.ppm
52 To increase brightness by compression-
55 pamlevels \
56 -f1 black -t1 black -f2 white -t2 white \
57 -f3 white:0.5 -t3 white:0.6 in.ppm > out.ppm
58 The latter tranformation is similar to gamma-correction.
60
64 In addition to the options common to all programs based on libnetpbm
65 (most notably -quiet, see
66 Common Options ⟨index.html#commonoptions⟩ ), pamlevels recognizes the
67 following command line options:
68 -from1
72 -to1
74 -from2
76 -to2
78 -from3
80 -to3 These options define the mappings of input colors to output col‐
82 ors that anchor the transformation function. See DESCRIPTION
83 ⟨#description⟩ .
84 You must specify at least two of these pairs.
86 -linear
89 This option tells pamlevels to work with the intensity-linear
90 variation on PPM where the samples are proportional to light in‐
91 tensity, rather than brightness (gamma-adjusted) as in true PPM.
92 The input must be of this form and the pamlevels makes the out‐
93 put of this form.
94 Note that the numbers in a color specification like
96 rgbi:0.9/0.83/0.80 are brightness levels (gamma-adjusted) re‐
97 gardless of the input and output format.
98 You cannot use this with -fitbrightness because that function is
100 not implemented.
101 -fitbrightness
104 This option selects a transformation which is not very useful -
105 it is linear or quadratic in brightness rather than light inten‐
106 sity of the pixels. There is no physical basis for doing it
107 this way and the result is normally undesirable.
108 Note that many tools other than Netpbm do the transformation
110 this way. One use for this option is simply to demonstrate the
111 poor result of this method.
112 One advantage of this transformation is that it is faster, be‐
114 cause the input and output image formats use brightness values.
115 The result is approximately correct.
116 You cannot use this with -linear because that function is not
118 implemented.
119
124 pnmnorm(1), pamrecolor(1), pnmgamma(1), pnm(1)
125
128 This program was first submitted by Anton Shepelev (an‐
129 ton.txt@gmail.com).
130
133 pamlevels was new in Netpbm 10.83 (June 2018).
134
136 This manual page was generated by the Netpbm tool 'makeman' from HTML
137 source. The master documentation is at
138 http://netpbm.sourceforge.net/doc/pamlevels.html
140netpbm documentation 13 June 2018 Pamlevels User Manual(0)