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 color. Derived from the earlier XBM syntax, it is a plain text file of a C programming language syntax, which can be included in a C program file.

Read more about X PixMap:  XPM, XPM2, XPM3, Comparison With Other Formats, Application Support