Pgmtoppm User Manual(1) General Commands Manual Pgmtoppm User Manual(1)
NAME
pgmtoppm - colorize a PGM (grayscale) image into a PPM (color) image
SYNOPSIS
pgmtoppm [-black=colorspec1] [-white=colorspec2]
[pgmfile] pgmtoppm -map=filename [pgmfile] pgmtoppm colorspec [pgm-
file] pgmtoppm colorspec1-colorspec2 [pgmfile]
Minimum unique abbreviation of option is acceptable. You may use dou-
ble 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).
If all you want to do is convert PGM to PPM, keeping the same gray pix-
els,
you may not need to. All Netpbm programs that expect PPM input also
recognize PGM. And if you must have a PPM file, use ppmtoppm
instead. It is more efficient and easier to use.
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.
You can specify the color in the output to which black in the input
maps,
and the color to which white maps. All the gray values in between
map
linearly (across a three dimensional space) to colors between the
black and
white colors you specify.
Use the -black and -white options for this. For historical
reasons, you can alternatively use a non-option argument to specify
the
colors. If you do that, pgmtoppm interprets the color argument
like this: if the argument takes the form black-white,
it has the effect of -black=black -white=white
If instead there is no hyphen in the color argument, it has the ef-
fect of
-white=color_argument.
Because of the historical syntax, it is not possible to let both
-black and -white default (but you shouldn't want to --
see below for advice on making such a null conversion).
You can alternatively specify an entire colormap with the -map option.
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 ex-
plicitly associates a color with each possible gray level.
OPTIONS
In addition to the options common to all programs based on libnetpbm
(most notably -quiet, see
Common Options ⟨index.html#commonoptions⟩ ), pgmtoppm recognizes the
following command line options:
-black=colorspec
The program maps black pixels in the input to this color in the
output. The default is black.
Specify the color (color) as described for the argument of the
pnm_parsecolor() library routine
⟨libnetpbm_image.html#colorname⟩ .
You cannot specify this together with -map.
This option was new in Netpbm 10.97 (December 2021). Before
that,
use the color argument.
-white=colorspec
The program maps white pixels in the input to this color in the
output. The default is white.
Specify the color (color) as described for the argument of the
pnm_parsecolor() library routine
⟨libnetpbm_image.html#colorname⟩ .
You cannot specify this together with -map.
This option was new in Netpbm 10.97 (December 2021). Before
that,
use the color argument.
-map=filename
This option specifies a complete mapping of gray values in the
input to
color values in the output. The map file (named filename)
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.
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 res-
olution, 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 ei-
ther 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 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, 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 neces-
sary to represent a PBM image, pgmtoppm, like all Netpbm programs, in
fact treats it as a maxval of 255.
SEE ALSO
ppmtoppm(1), pamdepth(1), rgb3toppm(1), ppmtopgm(1), ppmtorgb3(1),
ppm(1), pgm(1)
AUTHOR
Copyright (C) 1991 by Jef Poskanzer.
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 02 October 2021 Pgmtoppm User Manual(1)
Generated by dwww version 1.15 on Sat Jun 29 01:57:33 CEST 2024.