This program is part of Netpbm.
ppmtopcx reads a PPM image as input and produces a PCX file as output. The type of the PCX file depends on the number of colors in the input image:
You can override some of that and explicitly choose the format with the options below.
This option was added in Netpbm 10.18 (August 2003).
The standard palette is not only a set of colors, but a specific mapping of palette indexes to colors. E.g. red is 4.
You can use pnmremap with a suitable PPM image of the standard palette to adapt your image to use exactly those colors in the palette so that ppmtopcx -stdpalette will work on it.
The file pcxstd.ppm, part of Netpbm, contains the standard palette.
Although the PCX header tells exactly what palette is used in the file, some older PCX interpreters do not use that information. They instead assume the standard palette. If you don't use the -stdpalette option, ppmtopcx, ppmtopcx may create an image that uses a different palette (a rearrangement of the same colors) and then one of these older interpreters would interpret the colors in the image wrong.
You cannot specify this option along with -palette.
This option was new in Netpbm 10.22 (April 2004).
The palette file must be a PPM image that contains one pixel for each color in the palette. It doesn't matter what the aspect ratio of the palette image is. The order of the colors in the PCX palette is the order of the pixels in the PPM image in standard western reading order (left to right, top to bottom). If there is a duplicate color in the palette, ppmtopcx chooses between them arbitrarily in building the PCX raster.
You would need this only if you have a PCX reader that can't read the palette that is in the PCX file and instead assumes some particular palette. See also the -stdpalette option.
If your input image might contain colors other than those in your palette, you can convert the input image to one that contains only those colors in your palette with pnmremap.
You cannot specify this along with -stdpalette.
This option was new in Netpbhm 10.25 (October 2004).
This is meaningful only when ppmtopcx generates an image in the 16 color palette format without packed pixels. Consequently, you cannot specify this option together with -24bit or -8bit or -packed.
The valid values for planes are 1, 2, 3, and 4. By default, ppmtopcx chooses the smallest number of planes that can represent the colors in the image. E.g. if there are 5 colors, ppmtopcx chooses 3 planes.
This option was new in Netpbm 10.21 (March 2004).
The values may be from -32767 to 32768.
The default for each is zero.
Based on previous work by Michael Davidson.