Pgmtoppm User Manual(0)                                Pgmtoppm User Manual(0)


       pgmtoppm - colorize a PGM (grayscale) image into a PPM (color) image




       [pgmfile] pgmtoppm


       [pgmfile] pgmtoppm -map




       This program is part of Netpbm(1).

       pgmtoppm  reads a PGM as input and produces a PPM file as output with a
       specific color assigned to each gray value in the input.

       If you specify one color argument, black in the pgm  file  stays  black
       and  white  in  the  pgm file turns into the specified color in the ppm
       file.  Gray values in between are linearly mapped to differing intensi-
       ties of the specified color.

       If  you  specify  two color arguments (separated by a dash), then black
       gets mapped to the first color and white gets mapped to the second  and
       gray  values in between get mapped linearly (across a three dimensional
       space) to colors in between.

       Specify the color (color) as described for the argument of the ppm_par-
       secolor() library routine .

       Also,  you  can  specify  an entire colormap with the -map option.  The
       mapfile is just a ppm file; it can be any shape, all  that  matters  is
       the colors in it and their order.  In this case, black gets mapped into
       the first color in the map file, and white gets mapped to the last  and
       gray  values in between are mapped linearly onto the sequence of colors
       in between.

       A more direct way to specify a particular color to replace each partic-
       ular  gray  level  is  to  use  pamlookup.  You make an index file that
       explicitly associates a color with each possible gray level.


       The ’maxval,’ or depth, of the output image is the same as that of  the
       input  image.  The maxval affects the color resolution, which may cause
       quantization errors you don’t anticipate in your output.  For  example,
       you  have  a  simple black and white image as a PGM with maxval 1.  Run
       this image through pgmtoppm 0f/00/00 to try to make the image black and
       faint  red.  Because the output image will also have maxval 1, there is
       no such thing as faint red.  It has to be either full-on red or  black.
       pgmtoppm rounds the color 0f/00/00 down to black, and you get an output
       image that is nothing but black.

       The fix is easy: Pass the input through pnmdepth on the way  into  pgm-
       toppm  to increase its depth to something that would give you the reso-
       lution you need to get your desired color.  In this case,  pnmdepth  16
       would  do  it.  Or spare yourself the unnecessary thinking and just say
       pnmdepth 255 .

       PBM input is a special case.  While  you  might  think  this  would  be
       equivalent to a PGM with maxval 1 since only two gray levels are neces-
       sary to represent a PBM image, pgmtoppm, like all Netpbm  programs,  in
       fact treats it as a maxval of 255.


       pnmdepth(1), rgb3toppm(1), ppmtopgm(1), ppmtorgb3(1), ppm(1), pgm(1)


       Copyright (C) 1991 by Jef Poskanzer.

netpbm documentation            24 January 2001        Pgmtoppm User Manual(0)

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