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Pamlookup User Manual(0)						 Pamlookup User Manual(0)

       pamlookup - map an image to a new image by using it as indices into a table

       pamlookup -lookupfile=lookupfile -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.

       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.  The output thus has the same width and height
       as the index image, and tuple types determined by the lookup table.

       An index is either a whole number or an ordered pair of whole numbers.  If the index image
       has  a  depth of one, each index in it is a whole number: the value of the one sample.  If
       the index image has a depth greater than one, each index in it is an ordered pair  of  the
       first and second samples in the relevant tuple.

       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 ta-
       ble.  If the index image contains ordered pair indices, the first element of  the  ordered
       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.

       For example:  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

       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
       green   black

       This lookup table says Index (0,0) corresponds to the color red, Index  (0,1)  corresponds
       to  yellow,  Index  (1,0) corresponds to green, and Index (1,1) corresponds to black.  The
       output of pamlookup is the following PPM image:

       red     yellow	red
       black   green	red

       If an index specifies a row or column that exceeds the  dimensions  of  the  lookup  table
       image, pamlookup uses the value from the top left corner of the lookup image, or the value
       you specify with the -missingcolor option.

       The indexfile argument identifies the file containing the index PAM or PNM image.  - means
       Standard  Input.   The  mandatory  -lookupfile  option  identifies the file containing the
       lookup table image.  Again, - 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.

       You can use ppmmake and pnmcat to create a lookup table file.

       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 combine the two into one two-plane  image
       (and use a 2-dimensional lookup table image).

	      lookupfile names the file that contains the PAM or PNM image that is the lookup ta-
	      ble.  This option is mandatory.

	      This option is meaningful only if the lookup image (and therefore 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 of -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  ppm_parsecolor()
	      library routine <libppm.html#colorname> .

	      Another way to deal with a too-small lookup image is to use the -fit option.

       -fit   This  option  says  to  shrink  or  expand the lookup image as necessary to fit the
	      indices present in the index image, per the index image's maxval.  For example,  if
	      your  index image has a single 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 pam-


	      When you use -fit, pamlookup never fails or warns you due to invalid  lookup  image
	      dimensions, and the -missingcolor option has no effect.

   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 sample 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 dri-
       est, 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 between.  Call it colorkey.ppm.

	   pamlookup rainfall.ppm -lookupfile=colorkey.ppm >rainfallmap.ppm

       Now lets say you're too lazy to type in 200 color values and nobody really cares about the
       places  that  have  more  than 99 centimeters of annual rainfall.  In that case, just make
       colorkey.ppm 100 columns wide and do this:

	   pamlookup rainfall.ppm -lookupfile=colorkey.ppm -missingcolor=black \

       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  back-
       ground where both images contain background and foreground where both images contain fore-
       ground.	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

       pnmremap(1) , ppmmake(1) , pnmcat(1) , pamstack(1) , pnm(1) , pam(1)

       pamlookup was new in Netpbm 10.13 (December 2002).

netpbm documentation			 10 November 2002		 Pamlookup User Manual(0)
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