MAC to PGM Converter

MAC (MacPaint) is a monochrome bitmap image format created by Bill Atkinson at Apple Computer and released alongside the original Macintosh on January 24, 1984. MacPaint was bundled with every Macintosh and became the first widely used painting application on a personal computer with a graphical user interface. MAC files store 1-bit (black and white) images at a fixed resolution of 576x720 pixels — matching the printable area of the original ImageWriter dot-matrix printer at 72 dpi — using PackBits run-length encoding compression. The file structure consists of a 512-byte header (largely unused, originally reserved for application data), followed by the compressed bitmap data organized as 720 rows of 72 bytes each (576 pixels per row, 8 pixels per byte). The PackBits scheme alternates between literal byte runs and repeated-byte runs, providing efficient compression for the large solid areas typical of black-and-white illustrations while imposing minimal computational overhead on the Macintosh's 7.8 MHz Motorola 68000 processor. One advantage is the format's historical significance — MacPaint and its file format helped establish the visual language of desktop computing, and the artwork created with it by early Macintosh users, including Susan Kare's iconic interface designs and fonts, represents a foundational chapter in computer graphics history. The format's extreme simplicity is another practical strength: MAC files can be decoded with trivial code, and the format is supported by ImageMagick, GIMP, XnView, and other modern image tools.