X PixMap

X PixMap (XPM) is an image file format used by the X Window System, created in 1989 by Daniel Dardailler and Colas Nahaboo working at Bull Research Center at Sophia Antipolis, France, and later enhanced by Arnaud Le Hors.
It is intended primarily for creating icon pixmaps, and supports transparent pixels. Derived from the earlier XBM syntax, it is a plain text file in the XPM2 format or of a C programming language syntax, which can be included in a C program file.
History.
XPM1.
The first (1989) XPM format is relatively similar to the XBM format. Compared to XBM, it uses additional macro definitions and variables for indexed colors, and replaces bits with characters for describing the image. The following is a black-and-white image in the 1989 XPM format.
static char *XFACE_colors[] = {
"a", "#ffffff",
"b", "#000000"
static char *XFACE_pixels[] = {
"abaabaababaaabaabababaabaabaababaabaaababaabaaab",
// and so on for 48 rows with 48 pixels
XPM2.
XPM2 (1990) simplifies the format by removing all C code. The structure is simplified to
The above file, with width 48, height 4, 2 colors, and 1 character per pixel, becomes:
Colors.
In addition to hexcodes, the colors can be any of the X11 color names. In addition, codice_2 indicates transparency.
The "symbolic" feature permits adjusting colors depending on the context where they are used. Code such as codice_3 could be adjusted on a blue background.
Many-color encoding.
One tool is known to use only a to p for 16 colors, switching to aa up to dp for 64 colors, but still reading single character encodings for 64 colors; compare Base64.
With more colors the codes use more characters, e.g. aa up to pp for 16 × 16 = 256 colors. This is less useful for text editors, because a string ab could be actually the middle of two adjacent pixels dabc. Spaces are allowed as color code, but might be a bad idea depending on the used text editor. Without control codes, backslash, and quote (needed in XPM1 and XPM3) 128 − 33 − 2 = 93 ASCII characters are available for single character color codes.
Simplified example: 90 US-ASCII characters could be arranged into nine non-overlapping sets of 10 characters. Thus unambiguous strings of nine characters could set the color of each pixel by its XPM palette index with up to 109 = colors (compare to GIF, which supports only 256).
For XPM2 it is clear how many lines belong to the image – two header lines, the second header line announcing the number of color codes (2 lines in the example above) and rows (height 4 in the example above), e.g. 2 + 2 + 4 = 8 lines.
XPM3.
The current and last format is XPM3 (1991). It re-introduces the C wrapper, but instead of explicitly showing a file's structure, the strings stored are essentially identical to XPM2.
/* XPM */
static char * XFACE[] = {
"48 4 2 1",
"a c #ffffff",
"b c #000000",
"abaabaababaaabaabababaabaabaababaabaaababaabaaab",
"abaabaababaaabaabababaabaabaababaabaaababaabaaab",
"abaabaababaaabaabababaabaabaababaabaaababaabaaab",
"abaabaababaaabaabababaabaabaababaabaaababaabaaab"
If the "values" line contains six instead of four numbers, the additional values indicate the coordinates of a "hotspot", where 0 0 is the upper left corner of a box containing the icon and the default. A "hotspot" is used for mouse pointers and similar applications.
Comparison with other formats.
The following code displays the same blarg file in the XBM, XPM and PBM formats.
XBM version:
static char test_bits[] = {
0x13, 0x00, 0x15, 0x00, 0x93, 0xcd, 0x55, 0xa5, 0x93, 0xc5, 0x00, 0x80,
0x00, 0x60 };
XPM2 version:
XPM3 version:
/* XPM */
static char * blarg_xpm[] = {
"16 7 2 1",
"* c #000000",
". c #ffffff",
"*.*.*...",
"*.*.*.*.*.*..*.*",
"...*",
};
PBM file:
Application support.
ACDSee, Amaya, CorelDRAW, GIMP, ImageMagick, IrfanView (formats plugin), PaintShop Pro, PMView, Photoshop (plugins), and XnView among others support XPM. Gravatar and picons also support XPM.
An X11 libXpm vulnerability was fixed in 2005,
2023
FFmpeg version 3.3 or later can decode XPM.