1Pamrecolor User Manual(0) Pamrecolor User Manual(0)
2
6 pamrecolor - alter colors without affecting luminance
7
10 pamrecolor [--colorspace=name] [--rmult=fraction] [--gmult=fraction]
11 [--bmult=fraction] [--targetcolor=color] [--colorfile=file] [infile]
12 Minimum unique abbreviation of option is acceptable. You may use dou‐
15 ble hyphens instead of single hyphen to denote options. You may use
16 white space in place of the equals sign to separate an option name from
17 its value.
18
21 This program is part of Netpbm(1).
22 pamrecolor changes an image's colors to be as close as possible to
24 given target colors but with the constraint that the luminance not be
25 modified. That is, the original image and the target image will look
26 identical if both are converted to grayscale (e.g. with ppm‐
27 topgm(1)).Youcanhavepamrecolorselect target colors randomly, specify a
28 single hue for the entire image, or take the target colors from a tar‐
29 get image.
30 pamrecolor works on pseudo-Netpbm images based on arbitrary color spa‐
32 ces. You can define the color space explicitly or choose on of many
33 that pamrecolor knows by name.
34 The output is a PAM image on standard output. Options control the
36 exact format of the PAM. If you want a PNM (PBM, PGM, or PPM) image,
37 use pamtopnm(1)ontheoutput.Thereisno need to convert if you will use
38 the image as input to a current Netpbm program, but many other programs
39 don't know what a PAM is.
40
44 --colorspace=name
45 Designate the color space to use for determining the contribu‐
46 tion to luminance of each of the red, green, and blue color
47 channels. For example, in the SMPTE-C color space an RGB color
48 is converted to grayscale by multiplying the red channel by
49 0.2124132, the green channel by 0.7010437, and the blue channel
50 by 0.0865432 and summing the resulting three products.
51 When you use this option, the input and output images are not
53 true Netpbm images, because the Netpbm image format specifies a
54 particular color space. Instead, you are using a variation on
55 the format in which the sample values in the raster have differ‐
56 ent meaning. Many programs that ostensibly use Netpbm images
57 actually use a variation with a different color space, For exam‐
58 ple, GIMP ⟨http://www.gimp.org/⟩ uses sRGB internally and if
59 you have GIMP generate a Netpbm image file, it really generates
60 a variation of the format that uses sRGB.
61 pamrecolor knows the following color spaces (name values):
63 adobe
67 Adobe RGB (1998) with a D65 reference white
69 apple
72 Apple RGB with a D65 reference white
74 cie
77 CIE with an Illuminant E reference white
79 ntsc
82 NTSC RGB with an Illuminant C reference white
84 pal
87 PAL/SECAM with a D65 reference white
89 smpte-c
92 SMPTE-C with a D65 reference white
94 srgb
97 sRGB with a D65 reference white
99 wide
102 Wide-gamut RGB with a D50 reference white
104 The default is <q>ntsc</q> because this is the color space that
107 the Netpbm format of Netpbm and many other graphics utilities.
108 As a counterexample, GIMP ⟨http://www.gimp.org/⟩ uses sRGB as
109 its native color space.
110 The luminance values pamrecolor uses for each of the above come
112 from Bruce Lindbloom's Computing RGB-to-XYZ and XYZ-to-RGB
113 matrices (1) page.
114 --rmult=fraction
117 --gmult=fraction
119 --bmult=fraction
121 Instead of selecting a color space by name, you can specify
122 explicitly the contribution of each color channel to the overall
123 luminance as red, green, and blue multipliers. These three
124 options must be used together, and the three fraction values
125 must sum to 1.0. For example, you can specify the ProPhoto
126 (ROMM) RGB color space with <q>--rmult=0.2880402
127 --gmult=0.7118741 --bmult=0.0000857</q>.
128 --targetcolor=color
131 Designate color as the target color for the image. pamrecolor
132 will make each pixel as close as possible to color subject to
133 the constraint that the luminance must stay the same as in the
134 original image. Specify color as in the argument of the
135 ppm_parsecolor() library routine ⟨libppm.html#colorname⟩
136 (e.g., <q>hotpink</q> or <q>#ff69b4</q>).
137 If you specify neither --targetcolor nor --colorfile, pamrecolor
139 will randomly select a target color for each pixel of the input
140 image.
141 You may not specify both -targetcolor and -colorfile.
143 --colorfile=file
148 Take per-pixel target colors from Netpbm file file instead of
149 using a single target color for the entire image. file should
150 be a PPM or color PAM image. If the image in the file wider or
151 taller than the input image, pamrecolor uses only the left and
152 top part of it. If the image is narrower or shorter, pamrecolor
153 considers the image to be repeated in a tile pattern.
154 If you specify neither --targetcolor nor --colorfile, pamrecolor
156 will randomly select a target color for each pixel of the input
157 image.
158 You may not specify both -targetcolor and -colorfile.
160
166 This command tints an image yellow:
167 pamrecolor --targetcolor=yellow colorpic.pam > yellowpic.pam
169 This command takes the colors from colorpicture.ppm and applies them to
171 graypicture.pgm:
172 pamrecolor --colorfile=colorpic.ppm graypic.pgm > colorizedpic.pam
174 The grayscale version of colorizedpic.pam will look just like
176 graypic.pgm. Note that if you use a non-Netpbm tool to do the conver‐
177 sion to grayscale, you may additionally need to specify an appropriate
178 --colorspace value for your conversion tool.
179
183 Here are a couple of fun special effects you can produce with pamre‐
184 color:
185 · Specify a color file that is identical to the input image but
189 with some large, colored text added to it. The text will
190 <q>magically</q> vanish when the image is converted to
191 grayscale.
192 · Provide a low-contrast grayscale image — perhaps a secret
195 message written in similar shades of gray — as the input
196 file and a colorful but completely different image as the color
197 file. If done carefully, the grayscale image can be hidden by
198 the colorful image. Only people who know to convert the result
199 to grayscale can recover the original grayscale image.
200 · Use --targetcolor=tan to make an image look like an old-timey
203 photograph (or, more precisely, a sepia-toned photograph
204 ⟨http://en.wikipedia.org/wiki/Photographic_print_toning⟩ of the
205 late 1800s).
206
211 Scott Pakin wrote pamrecolor in July 2010.
212 pamrecolor was new in Netpbm 10.52 (September 2010).
214
218 Copyright (C) 2010 Scott Pakin, scott+pbm@pakin.org.
219
223 ·
224 ppmtopgm(1)
226 ·
228 ppmchange(1)
230 ·
232 pnmremap(1)
234netpbm documentation 31 July 2010 Pamrecolor User Manual(0)