SK1 to XBM Converter

XBM (X BitMap) is a monochrome (1-bit) image format defined as part of the X Window System, originating at MIT around 1987. XBM files are unique among image formats in being valid C source code: each file defines the image as a static array of unsigned char values containing the packed pixel data, preceded by #define statements specifying the image width, height, and optional hot-spot coordinates (for cursor images). The pixel data is stored in hexadecimal byte values within curly braces, with each bit representing one pixel (1 = foreground, 0 = background) and bits ordered LSB-first within each byte. This design was intentional — XBM images could be #included directly into X Window application source code and compiled into the binary, eliminating the need for external file loading and runtime format parsing. The format was used throughout the X11 ecosystem for cursor shapes, window icons, toolbar buttons, and other small UI elements. One advantage is the source-code nature of the format: XBM files can be edited with a text editor, diff'd and merged in version control, generated by shell scripts, and compiled directly into C programs without any image loading library — a level of toolchain integration that no binary image format can match. The format's role as part of the X Window standard ensures it is understood by every X11-aware toolkit and application. While limited to monochrome and no compression, XBM's simplicity makes it an excellent teaching format for understanding bitmap representations. XBM files are supported by all X11 applications, ImageMagick, GIMP, web browsers (as a legacy web format), and programming environments.