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
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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
26 This program is part of Netpbm(1).
27 ppmchange reads a PPM image as input and changes all pixels of color
29 oldcolor to color newcolor.
30 You may specify up to 256 oldcolor/newcolor pairs on the command line.
32 ppmchange leaves all colors not mentioned unchanged, unless you specify
33 the -remainder option, in which case they are all changed to the single
34 specified color.
35 You can specify that colors similar, but not identical, to the ones you
37 specify get replaced by specifying a "closeness" factor.
38 Specify the colors as described for the argument of the
40 pnm_parsecolor() library routine ⟨libnetpbm_image.html#colorname⟩ .
41 If a pixel matches two different oldcolors, ppmchange replaces it with
43 the newcolor of the leftmost specified one.
44 The maxval of the output image is the same as that of the input image.
46 If a newcolor you specify cannot be exactly represented in that maxval,
47 ppmchange assumes a color that is as close as possible to what you
48 specified but can be represented with your maxval. Unless you specify
49 the -closeok option, ppmchange issues a warning that it is using an
50 approximation.
51 A common way that you can have this maxval problem, where the color you
53 specify cannot be represented with your maxval, is that your input is a
54 PBM (black and white) image that you are colorizing. The maxval in
55 this case is 1, which severely limits the colors to which you can
56 change. To avoid this problem, use pamdepth to make the maxval of your
57 input something consistent with your colors. 255 is usually a good
58 choice.
59 Before Netpbm 10.22 (April 2004), ppmchange always behaved as if the
61 user specified -closeok and there was no -closeok option.
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66 -closeness closeness_percent
67 closeness is a percentage indicating how close to the color you
68 specified a pixel must be to get replaced. By default, it is 0,
69 which means the pixel must be the exact color you specified.
70 A pixel gets replaced if the distance in color between it and
72 the color you specified is less than or equal to closeness per
73 cent of the maxval.
74 The "distance" in color is defined as the Cartesian sum of the
76 individual differences in red, green, and blue intensities
77 between the two pixels, normalized so that the difference
78 between black and white is 100%.
79 This is probably simpler than what you want most the time. You
81 probably would like to change colors that have similar chromi‐
82 nance, regardless of their intensity. So if there's a red barn
83 that is variously shadowed, you want the entire barn changed.
84 But because the shadowing significantly changes the color
85 according to ppmchange's distance formula, parts of the barn are
86 probably about as distant in color from other parts of the barn
87 as they are from green grass next to the barn.
88 Maybe ppmchange will be enhanced some day to do chrominance
90 analysis.
91 This option was new in Netpbm 9.8 (September 2000).
93 -closeok
96 This option affects how ppmchange interprets a color you specify
97 in the arguments. When you specify this option, ppmchange may
98 use a color close to, but not the same as what you specify. See
99 the description section ⟨#description⟩ for details.
100 This option was new in Netpbm 10.22 (April 2004). Before that,
102 ppmchange always behaved as if you specified this option.
103 -remainder color
106 ppmchange changes all pixels which are not of a color for which
107 you specify an explicit replacement color on the command line to
108 color color.
109 An example application of this is
111 ppmchange -remainder=black red red
113 to lift only the red portions from an image, or
115 ppmchange -remainder=black red white | ppmtopgm
116 to create a mask file for the red portions of the image.
118
123 pgmtoppm(1), ppmcolormask(1), ppm(1)
124
127 Wilson H. Bent. Jr. (whb@usc.edu) with modifications by Alberto Acco‐
128 mazzi (alberto@cfa.harvard.edu)
129
131 This manual page was generated by the Netpbm tool 'makeman' from HTML
132 source. The master documentation is at
133 http://netpbm.sourceforge.net/doc/ppmchange.html
135netpbm documentation December 2016 Ppmchange User Manual(0)