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.
This program is part of Netpbm.
ppmtoxpm reads a PPM image as input and produces X11 pixmap (version 3) as output. This format can be loaded by the XPM library.
In the XPM output, colors may be identified by name, such as "Red", or in hexadecimal, for example "#FF0000". In the hexadecimal format, there may be from 1 through 4 hexadecimal digits per RGB component.
By default, ppmtoxpbm tries to find a name for each color in the image in the system color dictionary, and if it finds one, uses it. If it doesn't it uses hexadecimal. You can force ppmtoxpbm to use hexadecimal only with the -hexonly option. You can specify a different color dictionary with the -rgb option.
When ppmtoxpm uses the hexadecimal format for identifying a color, it uses the one that uses the least number of hexadecimal digits that it takes to represent the maxval of the input PPM. E.g. if the maxval of the input PPM is 100, ppmtoxpm uses 2 digits per component, as in "#FF0000".
Some programs do not properly handle one-digit-per-component hexadecimal color specifiers. They see the wrong colors. To produce an XPM that such a program can handle, make sure the maxval of the input PPM is greater than 15, such as by running it through pamdepth 255.
In the XPM format, there is a palette ("color map") that assigns each color in the image to a unique sequence of printable characters called a color code, and a raster that identifies the color of each pixel of the image with one of those color codes. The length of the color code affects the size of the image stream.
All color codes in an image are the same length, and ppmtoxpm tries to make it as short as possible. That length is, of course, determined by the number of colors in the image. ppmtoxpm counts the colors in the image, excluding those that will be transparent in the output because of your transparency mask, and chooses a color code length accordingly. There are 92 printable characters that can be used in a color code. Therefore, if you have 92 or fewer colors, your color codes will be one character. If you have more than 92 but not more than 92 * 92, your color codes will be two characters. And so on.
There's one exception to the above: If you specify a transparency mask (the -alpha option, one unique color code represents "transparent." This is true even if the transparency mask doesn't actually produce any transparent pixels. So subtract one from the number of possible colors if you use -alpha.
This option was introduced in Netpbm 10.15 (April 2003). Before that, it was the default, overridden by specifying -rgb.
This option in meaningless when you specify -hexonly.
Before Netpbm 10.15 (April 2003), ppmtoxpm did not default to the system color dictionary. If you didn't specify -rgb, ppmtoxpbm would use only hexadecimal color specifiers.
If you don't specify -alphamask, ppmtoxpm makes all pixels in the output opaque.
ppmcolormask is one way to generate a transparency mask file. You might also generate it by extracting transparency information from an XPM file with the -alphaout option to xpmtoppm.
There are similar options on other Netpbm converters that convert from formats that include transparency information too.
Copyright (C) 1990 by Mark W. Snitily.
Permission to use, copy, modify, and distribute this software and its documentation for any purpose and without fee is hereby granted, provided that the above copyright notice appear in all copies and that both that copyright notice and this permission notice appear in supporting documentation. This software is provided "as is" without express or implied warranty.
This tool was developed for Schlumberger Technologies, ATE Division, and with their permission is being made available to the public with the above copyright notice and permission notice.
Upgraded to XPM2 by Paul Breslaw, Mecasoft SA, Zurich, Switzerland (email@example.com), November 8, 1990.
Upgraded to XPM version 3 by Arnaud Le Hors(firstname.lastname@example.org), April 9, 1991.