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
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11 pamlookup -lookupfile=lookupfile -missingcolor=color [-fit] indexfile
12 All options can be abbreviated to their shortest unique prefix. You
14 may use two hyphens instead of one. You may separate an option name
15 and its value with white space instead of an equals sign.
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19 This program is part of Netpbm(1).
20 pamlookup takes a two dimensional array of indices and a lookup table
22 as input. For each position in the index array, it looks up the index
23 in the lookup table and places the result of the lookup in the output
24 image. The output thus has the same width and height as the index
25 image, and tuple types determined by the lookup table.
26 An index is either a whole number or an ordered pair of whole numbers.
28 If the index image has a depth of one, each index in it is a whole num‐
29 ber: the value of the one sample. If the index image has a depth
30 greater than one, each index in it is an ordered pair of the first and
31 second samples in the relevant tuple.
32 The lookup table is a PAM or PNM image. If the index image contains
34 whole number indices, the lookup image is a single row and the index is
35 a column number. The lookup result is the value of the tuple or pixel
36 at the indicated column in the one row in the lookup table. If the
37 index image contains ordered pair indices, the first element of the
38 ordered pair is a row number and the second element of the ordered pair
39 is a column number. The lookup result is the value of the tuple or
40 pixel at the indicated row and column in the lookup table.
41 For example: Consider an index image consisting of a 3x2x1 PAM as fol‐
43 lows:
44 0 1 0
47 2 2 2
48 and a lookup table consisting of a 3x1 PPM image as follows:
50 red yellow beige
53 The lookup table above says Index 0 corresponds to the color red, Index
55 1 corresponds to yellow, and Index 2 corresponds to beige. The output
56 of pamlookup is the following PPM image:
57 red yellow red
60 beige beige beige
61 Now let's look at an example of the more complex case where the indices
63 are ordered pairs of whole numbers instead of whole numbers. Our index
64 image will be this 3x2x2 PAM image:
65 (0,0) (0,1) (0,0)
68 (1,1) (1,0) (0,0)
69 Our lookup table for the example will be this two dimensional PPM:
71 red yellow
74 green black
75 This lookup table says Index (0,0) corresponds to the color red, Index
77 (0,1) corresponds to yellow, Index (1,0) corresponds to green, and
78 Index (1,1) corresponds to black. The output of pamlookup is the fol‐
79 lowing PPM image:
80 red yellow red
83 black green red
84 If an index specifies a row or column that exceeds the dimensions of
86 the lookup table image, pamlookup uses the value from the top left cor‐
87 ner of the lookup image, or the value you specify with the -missing‐
88 color option.
89 The indexfile argument identifies the file containing the index PAM or
91 PNM image. - means Standard Input. The mandatory -lookupfile option
92 identifies the file containing the lookup table image. Again, - means
93 Standard Input. It won't work if both the index image file and lookup
94 table file are Standard Input. The output image goes to Standard Out‐
95 put.
96 You can use ppmmake and pnmcat to create a lookup table file.
98 If you want to use two separate 1-plane images as indices (so that your
100 output reflects the combination of both inputs), use pamstack to com‐
101 bine the two into one two-plane image (and use a 2-dimensional lookup
102 table image).
103
107 -lookupfile=lookupfile
108 lookupfile names the file that contains the PAM or PNM image
109 that is the lookup table. This option is mandatory.
110 -missingcolor=color
113 This option is meaningful only if the lookup image (and there‐
114 fore the output) is a PNM image. color specifies the color that
115 is to go in the output wherever the index from the input is not
116 present in the lookup table (not present means the index exceeds
117 the dimensions of the lookup image -- e.g. index is 100 but the
118 lookup image is a 50 x 1 PPM).
119 If you don't specify this option of -fit, pamlookup uses the
121 value from the top left corner of the lookup image whenever an
122 index exceeds the dimensions of the lookup image.
123 Specify the color (color) as described for the argument of the
125 ppm_parsecolor() library routine ⟨libppm.html#colorname⟩ .
126 Another way to deal with a too-small lookup image is to use the
128 -fit option.
129 -fit This option says to shrink or expand the lookup image as neces‐
132 sary to fit the indices present in the index image, per the
133 index image's maxval. For example, if your index image has a
134 single plane and a maxval of 255 and your lookup image is 1 row
135 of 10 columns, pamlookup stretches your lookup image to 255 col‐
136 umns before doing the lookups. pamlookup does the stretching
137 (or shrinking) with the pamscale(1) program.
138 When you use -fit, pamlookup never fails or warns you due to
140 invalid lookup image dimensions, and the -missingcolor option
141 has no effect.
142
147 Example: rainfall map
148 Say you have a set of rainfall data in a single plane PAM image. The
149 rows and columns of the PAM indicate lattitude and longitude. The sam‐
150 ple values are the annual rainfall in (whole) centimeters. The highest
151 rainfall value in the image is 199 centimeters. The image is in the
152 file rainfall.pam.
153 You want to produce a PPM rainfall map with green for the wettest
155 places, red for the driest, and other colors in between.
156 First, compose a lookup table image, probably with a graphical editor
158 and the image blown way up so you can work with individual pixels. The
159 image must have a single row and 200 columns. Make the leftmost pixel
160 red and the rightmost pixel green and choose appropriate colors in
161 between. Call it colorkey.ppm.
162 pamlookup rainfall.ppm -lookupfile=colorkey.ppm >rainfallmap.ppm
164 Now lets say you're too lazy to type in 200 color values and nobody
166 really cares about the places that have more than 99 centimeters of
167 annual rainfall. In that case, just make colorkey.ppm 100 columns wide
168 and do this:
169 pamlookup rainfall.ppm -lookupfile=colorkey.ppm -missingcolor=black >rainfallmap.ppm
171 Now if there are areas that get more than 100 centimeters of rainfall,
173 they will just show up black in the output.
174 Example: graphical diff
177 Say you want to compare two PBM (black and white) images visually.
178 Each consists of black foreground pixels on a white background. You
179 want to create an image that contains background where both images con‐
180 tain background and foreground where both images contain foreground.
181 But where Image 1 has a foreground pixel and Image 2 does not, you want
182 red in the output; where Image 2 has a foreground pixel and Image 1
183 does not, you want green.
184 First, we create a single image that contains the information from both
186 input PBMs:
187 pamstack image1.pbm image2.pbm >bothimages.pam
189 Note that this image has 1 of 4 possible tuple values at each location:
191 (0,0), (0,1), (1,0), or (1,1).
192 Now, we create a lookup table that we can index with those 4 values:
194 ppmmake white 1 1 >white.ppm
196 ppmmake black 1 1 >black.ppm
197 ppmmake red 1 1 >red.ppm
198 ppmmake green 1 1 >green.ppm
199 pnmcat -leftright black.ppm red.ppm >blackred.ppm
200 pnmcat -leftright green.ppm white.ppm >greenwhite.ppm
201 pnmcat -topbottom blackred.ppm greenwhite.ppm >lookup.ppm
202 Finally, we look up the indices from our index in our lookup table and
204 produce the output:
205 pamlookup bothimages.ppm -lookupfile=lookup.ppm >imagediff.ppm
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211 pnmremap(1), ppmmake(1), pnmcat(1), pamstack(1), pnm(1), pam(1)
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216 pamlookup was new in Netpbm 10.13 (December 2002).
217netpbm documentation 10 November 2002 Pamlookup User Manual(0)