XPM

XPM, short for X PixMap, is a plain-text image format used by the X Window System. It is designed to store small icons and cursors in a human-readable form that can be embedded directly in C source code or header files, facilitating easy inclusion in applications without separate image loading.

The format is ASCII-based. The first line of an XPM image specifies width, height, number of colors, and the number of characters per pixel (cpp). This is followed by color definition lines that map single-character symbols to color values or to None for transparency. The remaining lines contain the pixel data, with each character representing one pixel. Because the data are encoded as characters, XPM images are compact for simple icons but not optimal for photographic content.

XPM data are typically stored as a C array of strings, which enables icons to be compiled into applications. A small example in C form might look like:

static char * icon_xpm[] = {

"4 4 2 1",

"a c None",

"b c #000000",

"bbbb",

"bbab",

"bbba",

"bbbb"

};

This format supports embedding, easy version control, and straightforward editing with text tools. It is widely supported by the libXpm library and various X11 toolkits, and can be converted to other formats using image conversion tools such as ImageMagick or GIMP.

History and usage: XPM was introduced in the late 1980s for the X Window System and became a common choice for icons and cursors in early X11 environments. While binary formats like PNG have largely supplanted XPM for many applications, XPM remains available for compatibility and for scenarios where source-code embedding is desirable.

Limitations and related tools: As a text-based format, XPM is easy to inspect and diff but inefficient for large images and lacks rich metadata. Creating or converting XPM images is supported by tools such as Xpm, ImageMagick, and GIMP.