Pamlookup User Manual(1) General Commands Manual Pamlookup User Manual(1)
NAME
pamlookup - map an image to a new image by using it as indices into a
table
SYNOPSIS
pamlookup -lookupfile=lookupfile [-byplane] -missingcolor=color [-fit]
indexfile
All options can be abbreviated to their shortest unique prefix. You
may use two hyphens instead of one. You may separate an option name
and its value with white space instead of an equals sign.
DESCRIPTION
This program is part of Netpbm(1).
pamlookup takes a two dimensional array of indices and a lookup table
as input. For each position in the index array, it looks up the index
in the lookup table and places the result of the lookup in the output
image.
There are two ways of indexing the lookup table: whole tuple and by
plane. The -byplane option controls which pamlookup does.
In the simplest form of whole tuple indexing, each index in the index
array is a single whole number and the lookup table associates a whole
tuple with each possible whole number index. So for example, the index
array might have at Row 2, Column 9 the value 23. The lookup table
might associate the tuple (1,2,3) with the value 23. In that case, the
output image contains the tuple (1,2,3) at Row 2, Column 9.
In a more complex form of whole tuple indexing, each index in the index
array is an ordered pair of whole numbers and the lookup table asso-
ciates a whole tuple with each possible ordered pair index. Modifying
the example above, the index value could be (23, 5) instead of 23.
With whole tuple indexing, the output thus has the same width and
height as the index image, and tuple depth and type and maxval deter-
mined by the lookup table.
With whole tuple indexing, if the index image has depth 1, its sample
values are single whole number indices. If the index image has depth
greater than 1, its tuples are ordered pair indices composed of the
first and second sample in the tuple.
In by plane indexing, the index image contains whole number indices.
The first sample of each tuple in the index image is the index. The
lookup table maps each whole number index to another whole number.
pamlookup looks up each sample from the index image in the lookup table
and uses the resulting whole number as the sample value for the same
row, column, and plane in the output.
With by plane indexing, the output thus has the same dimensions as the
index image an the same maxval as the lookup image.
The Lookup Table Image
The lookup table is a PAM or PNM image. If the index image contains
whole number indices, the lookup image is a single row and the index is
a column number. The lookup result is the value of the tuple or pixel
at the indicated column in the one row in the lookup table. If the in-
dex image contains ordered pair indices, the first element of the or-
dered pair is a row number and the second element of the ordered pair
is a column number. The lookup result is the value of the tuple or
pixel at the indicated row and column in the lookup table.
The width of the lookup image should normally be the maxval of the in-
dex image plus one, so that each possible index sample value corre-
sponds to one entry in the lookup table. There are two ways pamlookup
deals with a lookup image that does not have such a width:
• Scale the lookup image to the required width. pamlookup always
does this with by plane indexing, and with whole tuple indexing,
does it when you specify -fit.
• Use a default value for indices that exceed the width of the
lookup image and ignore lookup image columns beyond the maxval
of the index image. pamlookup does this with whole tuple index-
ing when you don't specify -fit.
You specify the default value with a -missingcolor option; it
defaults to the value from the top left corner of the lookup im-
age.
With ordered pair indexes (which implies whole tuple indexing), the
same rule applies to the height of the index image as to the width.
The mandatory -lookupfile option identifies the file containing the
lookup table image. - means Standard Input. It won't work if both the
index image file and lookup table file are Standard Input.
You can use ppmmake and pnmcat to create a lookup table file.
Example - Whole Tuple Indexing
Here is an example of pamlookup's function with whole tuple indexing
(-byplane not specified).
Consider an index image consisting of a 3x2x1 PAM as follows:
0 1 0
2 2 2
and a lookup table consisting of a 3x1 PPM image as follows:
red yellow beige
The lookup table above says Index 0 corresponds to the color red, Index
1 corresponds to yellow, and Index 2 corresponds to beige. The output
of pamlookup is the following PPM image:
red yellow red
beige beige beige
Now let's look at an example of the more complex case where the indices
are ordered pairs of whole numbers instead of whole numbers. Our index
image will be this 3x2x2 PAM image:
(0,0) (0,1) (0,0)
(1,1) (1,0) (0,0)
Our lookup table for the example will be this two dimensional PPM:
red yellow red
black green red
Example - By Plane Indexing
Here is an example of pamlookup's function with by plane tuple indexing
(-byplane specified).
Consider an index image consisting of a 3x2x3 PAM as follows:
(0,0,0) (1,0,0) (2,0,0)
(2,2,0) (2,0,2) (2,0,0)
and a lookup table consisting of a 3x1x1 PAM image with maxval 7 as
follows:
3 4 7
The lookup table above says Index 0 corresponds to the sample value 3,
Index 1 corresponds to 4, and Index 2 corresponds to 7. The output of
pamlookup is the following 3x2x3 PAM image:
(3,3,3) (4,3,3) (7,3,3)
(7,7,3) (7,3,7) (7,3,3)
Miscellaneous
The indexfile argument identifies the file containing the index PAM or
PNM image. - means Standard Input. It won't work if both the index
image file and lookup table file are Standard Input.
The output image goes to Standard Output.
If you want to use two separate 1-plane images as indices (so that your
output reflects the combination of both inputs), use pamstack to com-
bine the two into one two-plane image (and use a 2-dimensional lookup
table image).
OPTIONS
In addition to the options common to all programs based on libnetpbm
(most notably -quiet, see
Common Options ⟨index.html#commonoptions⟩ ), pamlookup recognizes the
following command line options:
-lookupfile=lookupfile
lookupfile names the file that contains the PAM or PNM image
that is the lookup table. This option is mandatory.
-byplane
This options selects by plane indexing. The default is whole
tuple indexing.
This option was new in Netpbm 10.72 (September 2015). Before
that, there is no by plane indexing.
-missingcolor=color
This option is meaningful only if the lookup image (and there-
fore the output) is a PNM image. color specifies the color that
is to go in the output wherever the index from the input is not
present in the lookup table (not present means the index exceeds
the dimensions of the lookup image -- e.g. index is 100 but the
lookup image is a 50 x 1 PPM).
If you don't specify this option or -fit, pamlookup uses the
value from the top left corner of the lookup image whenever an
index exceeds the dimensions of the lookup image.
Specify the color (color) as described for the argument of the
pnm_parsecolor() library routine
⟨libnetpbm_image.html#colorname⟩ .
Another way to deal with a too-small lookup image is to use the
-fit option.
This option has no effect if you also specify -fit or -byplane.
-fit This option says to shrink or expand the lookup image as neces-
sary to fit the indices present in the index image, per the in-
dex image's maxval. For example, if your index image has a sin-
gle plane and a maxval of 255 and your lookup image is 1 row of
10 columns, pamlookup stretches your lookup image to 255 columns
before doing the lookups. pamlookup does the stretching (or
shrinking) with the pamscale(1) program.
When you use -fit, pamlookup never fails or warns you because of
invalid lookup image dimensions, and the -missingcolor option
has no effect.
-fit has no effect when you specify -byplane. pamlookup always
has the behavior requested by -fit when it does by plane index-
ing.
EXAMPLES
Example: rainfall map
Say you have a set of rainfall data in a single plane PAM image. The
rows and columns of the PAM indicate latitude and longitude. The sam-
ple values are the annual rainfall in (whole) centimeters. The highest
rainfall value in the image is 199 centimeters. The image is in the
file rainfall.pam.
You want to produce a PPM rainfall map with green for the wettest
places, red for the driest, and other colors in between.
First, compose a lookup table image, probably with a graphical editor
and the image blown way up so you can work with individual pixels. The
image must have a single row and 200 columns. Make the leftmost pixel
red and the rightmost pixel green and choose appropriate colors in be-
tween. Call it colorkey.ppm.
pamlookup rainfall.pam -lookupfile=colorkey.ppm >rainfallmap.ppm
Now lets say you're too lazy to type in 200 color values and nobody re-
ally cares about the places that have more than 99 centimeters of an-
nual rainfall. In that case, just make colorkey.ppm 100 columns wide
and do this:
pamlookup rainfall.ppm -lookupfile=colorkey.ppm -missingcolor=black \
>rainfallmap.ppm
Now if there are areas that get more than 100 centimeters of rainfall,
they will just show up black in the output.
Example: graphical diff
Say you want to compare two PBM (black and white) images visually.
Each consists of black foreground pixels on a white background. You
want to create an image that contains background where both images con-
tain background and foreground where both images contain foreground.
But where Image 1 has a foreground pixel and Image 2 does not, you want
red in the output; where Image 2 has a foreground pixel and Image 1
does not, you want green.
First, we create a single image that contains the information from both
input PBMs:
pamstack image1.pbm image2.pbm >bothimages.pam
Note that this image has 1 of 4 possible tuple values at each location:
(0,0), (0,1), (1,0), or (1,1).
Now, we create a lookup table that we can index with those 4 values:
ppmmake white 1 1 >white.ppm
ppmmake black 1 1 >black.ppm
ppmmake red 1 1 >red.ppm
ppmmake green 1 1 >green.ppm
pnmcat -leftright black.ppm red.ppm >blackred.ppm
pnmcat -leftright green.ppm white.ppm >greenwhite.ppm
pnmcat -topbottom blackred.ppm greenwhite.ppm >lookup.ppm
Finally, we look up the indices from our index in our lookup table and
produce the output:
pamlookup bothimages.ppm -lookupfile=lookup.ppm >imagediff.ppm
SEE ALSO
pamunlookup(1), pnmremap(1), ppmmake(1), pnmcat(1), pamstack(1),
pnm(1), pam(1)
HISTORY
pamlookup was new in Netpbm 10.13 (December 2002).
DOCUMENT SOURCE
This manual page was generated by the Netpbm tool 'makeman' from HTML
source. The master documentation is at
http://netpbm.sourceforge.net/doc/pamlookup.html
netpbm documentation 25 July 2015 Pamlookup User Manual(1)
Generated by dwww version 1.15 on Sat Jun 29 02:23:56 CEST 2024.