pamunlookup man page

pamunlookup — inverse of pamlookup


pamunlookup -lookupfile=lookupfile inputfile

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).

pamunlookup is best described as the inverse of pamlookup (without -byplane).  For example, the following normally yields output identical the input:

    $ cat input.ppm | \
        pamunlookup -lookupfile=map.pam | \
        pamlookup -lookupfile=map.pam \
        > output.ppm

Specifically, pamunlookup takes an input image and produces an output image of the same width and height in which each tuple is a single number.  That number is the index in a given lookup table of the tuple value that is in the same position in the input image.

You specify the lookup table the same way as for pamlookup .

Where a tuple in the input image is not in the lookup table, the number pamunlookup places in the output index image is one greater than the highest index in the lookup table.  Accordingly, the maxval of the output index image is the size of the lookup table.


Here is an example of pamunlookup's function.

Consider an input image consisting of a 3x2 PPM as follows:

red yellow red
beige beige beige

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 pamunlookup is the following index image:

0 1 0
2 2 2


The inputfile argument identifies the file containing the index PAM or PNM image.  - means Standard Input.  It won't work if both the input image file and lookup table file are Standard Input.

The output index image goes to Standard Output.



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


See Also

pamlookup(1), ppmchange(1), pnmcolormap(1), pnm(1), pam(1)


pamunlookup was new in Netpbm 10.72 (September 2015).

Document Source

This manual page was generated by the Netpbm tool 'makeman' from HTML source.  The master documentation is at

Referenced By


9 August 2015 netpbm documentation