1Ppmchange User Manual(0) Ppmchange User Manual(0)
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6 ppmchange - change all pixels of one color to another in a PPM image
7
10 ppmchange
11 [-closeness=closeness_percent] [-remainder=remainder_color] [-closeok]
13 [oldcolor newcolor] ... [ppmfile]
14
17 ppmchange red blue redimage.ppm >blueimage.ppm
18 ppmchange red red -remainder=black myimage.ppm >redblack.ppm
20 ppmchange -closeness=10 white white black black
22
27 This program is part of Netpbm(1).
28 ppmchange reads a PPM image as input and changes all pixels of color
30 oldcolor to color newcolor.
31 You may specify up to 256 oldcolor/newcolor pairs on the command line.
33 ppmchange leaves all colors not mentioned unchanged, unless you specify
34 the -remainder option, in which case they are all changed to the single
35 specified color.
36 You can specify that colors similar, but not identical, to the ones you
38 specify get replaced by specifying a "closeness" factor.
39 Specify the colors as described for the argument of the
41 pnm_parsecolor() library routine ⟨libnetpbm_image.html#colorname⟩ .
42 If a pixel matches two different oldcolors, ppmchange replaces it with
44 the newcolor of the leftmost specified one.
45 The maxval of the output image is the same as that of the input image.
47 If a newcolor you specify cannot be exactly represented in that maxval,
48 ppmchange assumes a color that is as close as possible to what you
49 specified but can be represented with your maxval. Unless you specify
50 the -closeok option, ppmchange issues a warning that it is using an ap‐
51 proximation.
52 A common way that you can have this maxval problem, where the color you
54 specify cannot be represented with your maxval, is that your input is a
55 PBM (black and white) image that you are colorizing. The maxval in
56 this case is 1, which severely limits the colors to which you can
57 change. To avoid this problem, use pamdepth to make the maxval of your
58 input something consistent with your colors. 255 is usually a good
59 choice.
60 Before Netpbm 10.22 (April 2004), ppmchange always behaved as if the
62 user specified -closeok, and there was no -closeok option.
63
67 In addition to the options common to all programs based on libnetpbm
68 (most notably -quiet, see
69 Common Options ⟨index.html#commonoptions⟩ ), ppmchange recognizes the
70 following command line options:
71 -closeness closeness_percent
75 closeness is a percentage indicating how close to the color you
76 specified a pixel must be to get replaced. By default, it is 0,
77 which means the pixel must be the exact color you specified.
78 A pixel gets replaced if the distance in color between it and
80 the color you specified is less than or equal to closeness per
81 cent of the maxval.
82 The "distance" in color is defined as the Cartesian sum of the
84 individual differences in red, green, and blue intensities be‐
85 tween the two pixels, normalized so that the difference between
86 black and white is 100%.
87 This is probably simpler than what you want most the time. You
89 probably would like to change colors that have similar chromi‐
90 nance, regardless of their intensity. So if there's a red barn
91 that is variously shadowed, you want the entire barn changed.
92 But because the shadowing significantly changes the color ac‐
93 cording to ppmchange's distance formula, parts of the barn are
94 probably about as distant in color from other parts of the barn
95 as they are from green grass next to the barn.
96 Maybe ppmchange will be enhanced some day to do chrominance
98 analysis.
99 This option was new in Netpbm 9.8 (September 2000).
101 -closeok
104 This option affects how ppmchange interprets a color you specify
105 in the arguments. When you specify this option, ppmchange may
106 use a color close to, but not the same as what you specify. See
107 the description section ⟨#description⟩ for details.
108 This option was new in Netpbm 10.22 (April 2004). Before that,
110 ppmchange always behaved as if you specified this option.
111 -remainder color
114 ppmchange changes all pixels which are not of a color for which
115 you specify an explicit replacement color on the command line to
116 color color.
117 An example application of this is
119 ppmchange -remainder=black red red
121 to lift only the red portions from an image, or
124 ppmchange -remainder=black red white | ppmtopgm
125 to create a mask file for the red portions of the image.
128
133 pgmtoppm(1), ppmcolormask(1), ppm(1)
134
137 Wilson H. Bent. Jr. (whb@usc.edu) with modifications by Alberto Acco‐
138 mazzi (alberto@cfa.harvard.edu)
139
141 This manual page was generated by the Netpbm tool 'makeman' from HTML
142 source. The master documentation is at
143 http://netpbm.sourceforge.net/doc/ppmchange.html
145netpbm documentation December 2016 Ppmchange User Manual(0)