1Pnmremap User Manual(0) Pnmremap User Manual(0)
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6 pnmremap - replace colors in a PNM image with colors from another set
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10 pnmremap
11 -mapfile=palettefile
13 [-floyd|-fs|-nfloyd|-nofs]
15 [-norandom]
17 [-firstisdefault]
19 [-verbose]
21 [-missingcolor=color]
23 [pnmfile]
25 All options can be abbreviated to their shortest unique prefix. You
27 may use two hyphens instead of one to designate an option. You may use
28 either white space or an equals sign between an option name and its
29 value.
30
33 This program is part of Netpbm(1).
34 pnmremap replaces the colors in an input image with those from a pal‐
36 ette you specify. Where colors in the input are present in the pal‐
37 ette, they just stay the same in the output. But where the input con‐
38 tains a color that is not in the palette, pnmremap gives you these
39 choices:
40 · Choose the closest color from the palette.
44 · Choose the first color from the palette.
47 · Use a color specified by a command option (-missing).
50 · Dither. This means rather than mapping pixel by pixel, pnmremap
53 uses colors from the palette to try to make multi-pixel regions
54 of the output have the same average color as the input (for
55 another kind of dithering, see ppmdither).
56 Two reasons to use this program are: 1) you want to reduce the number
60 of colors in the input image; and 2) you need to feed the image to
61 something that can handle only certain colors.
62 To reduce colors, you can generate the palette with pnmcolormap.
64 By default, pnmremap maps an input color that is not in the palette to
66 the closest color that is in the palette. Closest means with the
67 smallest cartesian distance in the red, green, blue brightness space
68 (smallest sum of the squares of the differences in red, green, and blue
69 ITU-R Recommedation BT.709 gamma-adjusted intensities).
70 You can instead specify a single default color for pnmremap to use for
72 any color in the input image that is not in the palette. Use the
73 -missing option for this.
74 You can also specify that the first color in the palette image is the
76 default. Use the -firstisdefault option for this.
77 The palette is simply a PNM image. The colors of the pixels in the
79 image are the colors in the palette. Where the pixels appear in the
80 image, and the dimensions of the image, are irrelevant. Multiple pix‐
81 els of the same color are fine. However, a palette image is typically
82 a single row with one pixel per color.
83 If you specify -missing, the color you so specify is in the palette in
85 addition to whatever is in the palette image.
86 For historical reasons, Netpbm sometimes calls the palette a 'col‐
88 ormap.' But it doesn't really map anything. pnmremap creates its own
89 map, based on the palette, to map colors from the input image to output
90 colors.
91 Palette/Image Type Mismatch
94 In the simple case, the palette image is of the same depth (number of
95 planes, i.e. number of components in each tuple (pixel)) as the input
96 image and pnmremap just does a straightforward search of the palette
97 for each input tuple (pixel). In fact, pnmremap doesn't even care if
98 the image is a visual image.
99 But what about when the depths differ? In that case, pnmremap converts
101 the input image (in its own memory) to match the palette and then pro‐
102 ceeds as above.
103 There are only two such cases in which pnmremap knows how to do the
105 conversion: when one of them is tuple type RGB, depth 3, and the other
106 is tuple type GRAYSCALE or BLACKANDWHITE, depth 1; and vice versa.
107 In any other case, pnmremap issues and error message and fails.
109 Note that as long as your input and palette images are PNM, they'll
111 always fall into one of the cases pnmremap can handle. There's an
112 issue only if you're using some exotic PAM image.
113 Before Netpbm 10.27 (March 2005), pnmremap could not handle the case of
115 a palette of greater depth than the input image. (It would issue an
116 error message and fail in that case).
117 In any case, the output image has the same tuple type and depth as the
119 palette image.
120 Multiple Image Stream
123 pnmremap handles a multiple image input stream, producing a multiple
124 image output stream. The input images need not be similar in any way.
125 Before Netpbm 10.30 (October 2005), pnmremap ignored any image after
127 the first.
128 Examples
132 pnmcolormap testimg.ppm 256 >palette.ppm
133 pnmremap -map=palette.ppm testimg.ppm >reduced_testimg.ppm
135 To limit colors to a certain set, a typical example is to create an
137 image for posting on the World Wide Web, where different browsers know
138 different colors. But all browsers are supposed to know the 216 'web
139 safe' colors which are essentially all the colors you can represent in
140 a PPM image with a maxval of 5. So you can do this:
141 pamseq 3 5 >websafe.pam
143 pnmremap -map=websafe.pam testimg.ppm >websafe_testimg.ppm
145 Another useful palette is one for the 8 color IBM TTL color set, which
147 you can create with
148 pamseq 3 1 >ibmttl.pam
149 If you want to quantize one image to use the colors in another one,
151 just use the second one as the palette. You don't have to reduce it
152 down to only one pixel of each color, just use it as is.
153 The output image has the same type and maxval as the palette image.
155
158 There is one parameter, which is required: The file specification of
159 the input PNM file.
160
164 -mapfile=palettefilename
165 This names the file that contains the palette image.
166 This option is mandatory.
168 -floyd
171 -fs
173 -nofloyd
175 -nofs These options determine whether Floyd-Steinberg dithering is
177 done. Without Floyd-Steinberg, the selection of output color of
178 a pixel is based on the color of only the corresponding input
179 pixel. With Floyd-Steinberg, multiple input pixels are consid‐
180 ered so that the average color of an area tends to stay more the
181 same than without Floyd-Steinberg. For example, if you map an
182 image with a black, gray, gray, and white pixel adjacent, to a
183 palette that contains only black and white, it might result in
184 an output of black, black, white, white. Pixel-by-pixel mapping
185 would instead map both the gray pixels to the same color.
186 Floyd-Steinberg gives vastly better results on images where
188 unmodified quantization has banding or other artifacts, espe‐
189 cially when going to a small number of colors such as the above
190 IBM set. However, it does take substantially more CPU time.
191 -fs is a synomym for -floyd. -nofs is a synonym for -nofloyd.
193 The default is -nofloyd.
195 -norandom
199 This option affects a detail of the Floyd-Steinberg dithering
200 process. It has no effect if you aren't doing Floyd-Steinberg
201 dithering.
202 By default, pnmremap initializes the error propagation accumula‐
204 tor to random values to avoid the appearance of unwanted pat‐
205 terns. This is an extension of the original Floyd-Steinberg
206 algorithm.
207 A drawback of this is that the same pnmremap on the same input
209 produces slightly different output every time, which makes com‐
210 parison difficult.
211 With -norandom, pnmremap initializes the error accumulators to
213 zero and the output is completely predictable.
214 -norandom was new in Netpbm 10.39 (June 2007).
216 -firstisdefault
220 This tells pnmremap to map any input color that is not in the
221 palette to the first color in the palette (the color of the
222 pixel in the top left corner of the palette image)
223 See DESCRIPTION ⟨#description⟩ .
225 If you specify -firstisdefault, the maxval of your input must
227 match the maxval of your palette image.
228 -missingcolor=color
231 This specifies the default color for pnmremap to map to a color
232 in the input image that isn't in the palette. color may or may
233 not be in the palette image; it is part of the palette regard‐
234 less.
235 If you specify -missingcolor, the maxval of your input must
237 match the maxval of your palette image.
238 -verbose
241 Display helpful messages about the mapping process.
242
248 pnmcolormap(1), pamseq(1), pnmquant(1), ppmquantall(1), pamdepth(1),
249 ppmdither(1), ppmquant(1), ppm(1)
250
253 Copyright (C) 1989, 1991 by Jef Poskanzer.
254netpbm documentation 01 January 2002 Pnmremap User Manual(0)