NAME¶
pgmtoppm - colorize a portable graymap into a portable pixmap
SYNOPSIS¶
pgmtoppm colorspec [
pgmfile]
pgmtoppm colorspec1-colorspec2 [
pgmfile]
pgmtoppm -map mapfile [
pgmfile]
DESCRIPTION¶
Reads a PGM as input. 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 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.
You can specify the color in one of five ways:
- o
- A name, from an X11-style color names file.
- o
- An X11-style hexadecimal specifier: rgb:r/g/b, where r g
and b are each 1- to 4-digit hexadecimal numbers.
- o
- An X11-style decimal specifier: rgbi:r/g/b, where r g and b
are floating point numbers between 0 and 1.
- o
- For backwards compatibility, an old-X11-style hexadecimal
number: #rgb, #rrggbb, #rrrgggbbb, or #rrrrggggbbbb.
- o
- For backwards compatibility, a triplet of numbers separated
by commas: r,g,b, where r g and b are floating point numbers between 0 and
1. (This style was added before MIT came up with the similar rgbi
style.)
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.
NOTE - MAXVAL¶
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 (in fact, let's say it's a PBM file, since
pgmtoppm, like all Netpbm programs, can accept a PBM file as if it were
PGM. The maxval of this image is 1, because only two gray values are needed:
black and white. 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
pgmtoppm to increase its depth to something that would give you the
resolution 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 .
SEE ALSO¶
pnmdepth(1),
rgb3toppm(1),
ppmtopgm(1),
ppmtorgb3(1),
ppm(5),
pgm(5)
AUTHOR¶
Copyright (C) 1991 by Jef Poskanzer.