1Pamlookup User Manual(0) Pamlookup User Manual(0)
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6 pamlookup - map an image to a new image by using it as indices into a
7 table
8
11 pamlookup -lookupfile=lookupfile [-byplane] -missingcolor=color [-fit]
12 indexfile
13 All options can be abbreviated to their shortest unique prefix. You
15 may use two hyphens instead of one. You may separate an option name
16 and its value with white space instead of an equals sign.
17
20 This program is part of Netpbm(1).
21 pamlookup takes a two dimensional array of indices and a lookup table
23 as input. For each position in the index array, it looks up the index
24 in the lookup table and places the result of the lookup in the output
25 image.
26 There are two ways of indexing the lookup table: whole tuple and by
28 plane. The -byplane option controls which pamlookup does.
29 In the simplest form of whole tuple indexing, each index in the index
31 array is a single whole number and the lookup table associates a whole
32 tuple with each possible whole number index. So for example, the index
33 array might have at Row 2, Column 9 the value 23. The lookup table
34 might associate the tuple (1,2,3) with the value 23. In that case, the
35 output image contains the tuple (1,2,3) at Row 2, Column 9.
36 In a more complex form of whole tuple indexing, each index in the index
38 array is an ordered pair of whole numbers and the lookup table asso‐
39 ciates a whole tuple with each possible ordered pair index. Modifying
40 the example above, the index value could be (23, 5) instead of 23.
41 With whole tuple indexing, the output thus has the same width and
43 height as the index image, and tuple depth and type and maxval deter‐
44 mined by the lookup table.
45 With whole tuple indexing, if the index image has depth 1, its sample
47 values are single whole number indices. If the index image has depth
48 greater than 1, its tuples are ordered pair indices composed of the
49 first and second sample in the tuple.
50 In by plane indexing, the index image contains whole number indices.
52 The first sample of each tuple in the index image is the index. The
53 lookup table maps each whole number index to another whole number.
54 pamlookup looks up each sample from the index image in the lookup table
55 and uses the resulting whole number as the sample value for the same
56 row, column, and plane in the output.
57 With by plane indexing, the output thus has the same dimensions as the
59 index image an the same maxval as the lookup image.
60 The Lookup Table Image
64 The lookup table is a PAM or PNM image. If the index image contains
65 whole number indices, the lookup image is a single row and the index is
66 a column number. The lookup result is the value of the tuple or pixel
67 at the indicated column in the one row in the lookup table. If the in‐
68 dex image contains ordered pair indices, the first element of the or‐
69 dered pair is a row number and the second element of the ordered pair
70 is a column number. The lookup result is the value of the tuple or
71 pixel at the indicated row and column in the lookup table.
72 The width of the lookup image should normally be the maxval of the in‐
74 dex image plus one, so that each possible index sample value corre‐
75 sponds to one entry in the lookup table. There are two ways pamlookup
76 deals with a lookup image that does not have such a width:
77 • Scale the lookup image to the required width. pamlookup always
81 does this with by plane indexing, and with whole tuple indexing,
82 does it when you specify -fit.
83 • Use a default value for indices that exceed the width of the
86 lookup image and ignore lookup image columns beyond the maxval
87 of the index image. pamlookup does this with whole tuple index‐
88 ing when you don't specify -fit.
89 You specify the default value with a -missingcolor option; it
91 defaults to the value from the top left corner of the lookup im‐
92 age.
93 With ordered pair indexes (which implies whole tuple indexing), the
96 same rule applies to the height of the index image as to the width.
97 The mandatory -lookupfile option identifies the file containing the
99 lookup table image. - means Standard Input. It won't work if both the
100 index image file and lookup table file are Standard Input.
101 You can use ppmmake and pnmcat to create a lookup table file.
103 Example - Whole Tuple Indexing
107 Here is an example of pamlookup's function with whole tuple indexing
108 (-byplane not specified).
109 Consider an index image consisting of a 3x2x1 PAM as follows:
111 0 1 0
114 2 2 2
115 and a lookup table consisting of a 3x1 PPM image as follows:
117 red yellow beige
120 The lookup table above says Index 0 corresponds to the color red, Index
122 1 corresponds to yellow, and Index 2 corresponds to beige. The output
123 of pamlookup is the following PPM image:
124 red yellow red
127 beige beige beige
128 Now let's look at an example of the more complex case where the indices
130 are ordered pairs of whole numbers instead of whole numbers. Our index
131 image will be this 3x2x2 PAM image:
132 (0,0) (0,1) (0,0)
135 (1,1) (1,0) (0,0)
136 Our lookup table for the example will be this two dimensional PPM:
138 red yellow red
141 black green red
142 Example - By Plane Indexing
146 Here is an example of pamlookup's function with by plane tuple indexing
147 (-byplane specified).
148 Consider an index image consisting of a 3x2x3 PAM as follows:
150 (0,0,0) (1,0,0) (2,0,0)
153 (2,2,0) (2,0,2) (2,0,0)
154 and a lookup table consisting of a 3x1x1 PAM image with maxval 7 as
156 follows:
157 3 4 7
160 The lookup table above says Index 0 corresponds to the sample value 3,
162 Index 1 corresponds to 4, and Index 2 corresponds to 7. The output of
163 pamlookup is the following 3x2x3 PAM image:
164 (3,3,3) (4,3,3) (7,3,3)
167 (7,7,3) (7,3,7) (7,3,3)
168 Miscellaneous
172 The indexfile argument identifies the file containing the index PAM or
173 PNM image. - means Standard Input. It won't work if both the index
174 image file and lookup table file are Standard Input.
175 The output image goes to Standard Output.
177 If you want to use two separate 1-plane images as indices (so that your
179 output reflects the combination of both inputs), use pamstack to com‐
180 bine the two into one two-plane image (and use a 2-dimensional lookup
181 table image).
182
186 In addition to the options common to all programs based on libnetpbm
187 (most notably -quiet, see
188 Common Options ⟨index.html#commonoptions⟩ ), pamlookup recognizes the
189 following command line options:
190 -lookupfile=lookupfile
194 lookupfile names the file that contains the PAM or PNM image
195 that is the lookup table. This option is mandatory.
196 -byplane
199 This options selects by plane indexing. The default is whole
200 tuple indexing.
201 This option was new in Netpbm 10.72 (September 2015). Before
203 that, there is no by plane indexing.
204 -missingcolor=color
207 This option is meaningful only if the lookup image (and there‐
208 fore the output) is a PNM image. color specifies the color that
209 is to go in the output wherever the index from the input is not
210 present in the lookup table (not present means the index exceeds
211 the dimensions of the lookup image -- e.g. index is 100 but the
212 lookup image is a 50 x 1 PPM).
213 If you don't specify this option or -fit, pamlookup uses the
215 value from the top left corner of the lookup image whenever an
216 index exceeds the dimensions of the lookup image.
217 Specify the color (color) as described for the argument of the
219 pnm_parsecolor() library routine
220 ⟨libnetpbm_image.html#colorname⟩ .
221 Another way to deal with a too-small lookup image is to use the
223 -fit option.
224 This option has no effect if you also specify -fit or -byplane.
226 -fit This option says to shrink or expand the lookup image as neces‐
229 sary to fit the indices present in the index image, per the in‐
230 dex image's maxval. For example, if your index image has a sin‐
231 gle plane and a maxval of 255 and your lookup image is 1 row of
232 10 columns, pamlookup stretches your lookup image to 255 columns
233 before doing the lookups. pamlookup does the stretching (or
234 shrinking) with the pamscale(1) program.
235 When you use -fit, pamlookup never fails or warns you because of
237 invalid lookup image dimensions, and the -missingcolor option
238 has no effect.
239 -fit has no effect when you specify -byplane. pamlookup always
241 has the behavior requested by -fit when it does by plane index‐
242 ing.
243
248 Example: rainfall map
249 Say you have a set of rainfall data in a single plane PAM image. The
250 rows and columns of the PAM indicate latitude and longitude. The sam‐
251 ple values are the annual rainfall in (whole) centimeters. The highest
252 rainfall value in the image is 199 centimeters. The image is in the
253 file rainfall.pam.
254 You want to produce a PPM rainfall map with green for the wettest
256 places, red for the driest, and other colors in between.
257 First, compose a lookup table image, probably with a graphical editor
259 and the image blown way up so you can work with individual pixels. The
260 image must have a single row and 200 columns. Make the leftmost pixel
261 red and the rightmost pixel green and choose appropriate colors in be‐
262 tween. Call it colorkey.ppm.
263 pamlookup rainfall.pam -lookupfile=colorkey.ppm >rainfallmap.ppm
265 Now lets say you're too lazy to type in 200 color values and nobody re‐
268 ally cares about the places that have more than 99 centimeters of an‐
269 nual rainfall. In that case, just make colorkey.ppm 100 columns wide
270 and do this:
271 pamlookup rainfall.ppm -lookupfile=colorkey.ppm -missingcolor=black \
273 >rainfallmap.ppm
274 Now if there are areas that get more than 100 centimeters of rainfall,
277 they will just show up black in the output.
278 Example: graphical diff
281 Say you want to compare two PBM (black and white) images visually.
282 Each consists of black foreground pixels on a white background. You
283 want to create an image that contains background where both images con‐
284 tain background and foreground where both images contain foreground.
285 But where Image 1 has a foreground pixel and Image 2 does not, you want
286 red in the output; where Image 2 has a foreground pixel and Image 1
287 does not, you want green.
288 First, we create a single image that contains the information from both
290 input PBMs:
291 pamstack image1.pbm image2.pbm >bothimages.pam
293 Note that this image has 1 of 4 possible tuple values at each location:
296 (0,0), (0,1), (1,0), or (1,1).
297 Now, we create a lookup table that we can index with those 4 values:
299 ppmmake white 1 1 >white.ppm
301 ppmmake black 1 1 >black.ppm
302 ppmmake red 1 1 >red.ppm
303 ppmmake green 1 1 >green.ppm
304 pnmcat -leftright black.ppm red.ppm >blackred.ppm
305 pnmcat -leftright green.ppm white.ppm >greenwhite.ppm
306 pnmcat -topbottom blackred.ppm greenwhite.ppm >lookup.ppm
307 Finally, we look up the indices from our index in our lookup table and
310 produce the output:
311 pamlookup bothimages.ppm -lookupfile=lookup.ppm >imagediff.ppm
313
318 pamunlookup(1), pnmremap(1), ppmmake(1), pnmcat(1), pamstack(1),
319 pnm(1), pam(1)
320
324 pamlookup was new in Netpbm 10.13 (December 2002).
325
327 This manual page was generated by the Netpbm tool 'makeman' from HTML
328 source. The master documentation is at
329 http://netpbm.sourceforge.net/doc/pamlookup.html
331netpbm documentation 25 July 2015 Pamlookup User Manual(0)