pgmtoppm(1) - phpMan

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

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

SYNOPSIS
pgmtoppm colorspec [pgmfile] pgmtoppm colorspec1-colorspec2 [pgmfile] pgmtoppm -map=map-
file [pgmfile]

Minimum unique abbreviation of option is acceptable. You may use double hyphens instead
of single hyphen to denote options. You may use white space in place of the equals sign
to separate an option name from its value.

DESCRIPTION
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 intensities of the specified color.

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

Specify the color (color) as described for the argument of the ppm_parsecolor() library
routine <libppm.html#colorname> .

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. The maxval of the output image is the maxval of the map image.

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

NOTE - MAXVAL
When you don't use -map, 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 pamdepth on the way into pgmtoppm to increase its
depth to something that would give you the resolution you need to get your desired color.
In this case, pamdepth 16 would do it. Or spare yourself the unnecessary thinking and
just say pamdepth 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 necessary to represent a PBM image, pgmtoppm, like
all Netpbm programs, in fact treats it as a maxval of 255.

SEE ALSO
pamdepth(1), rgb3toppm(1), ppmtopgm(1), ppmtorgb3(1), ppm(1), pgm(1)

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/pgmtoppm.html

netpbm documentation 10 December 2006 Pgmtoppm User Manual(0)

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