Grayscale image file encoded with either one or two bytes (8 or 16 bits) per pixel; contains header information and a grid of numbers that represent different shades of gray from black (0) to white (up to 65,536); typically stored in ASCII text format, but also has a binary representation. PGM files include a header that defines the PGM format type ("P2" for text or "P5" for binary), image width and height, and the maximum number of shades. While binary PGM files may contain multiple images, ASCII PGM files may only include one image.
The PGM file extension is also related to AKAI MPC family of devices. The MPC-1000, the MPC-2000, the MPC-2000XL and the MPC-3000 all use different program formats although they all have the same PGM file extension. Actually the MPC-2000 and MPC-2000XL use the same PGM file format, but the latter (like the MPC-1000) wants samples in WAV format, while the former wants them in SND format (like the MPC-3000).
A signature program is a small, highly condensed piece of code (commonly written in C or C++), usually three or fewer lines in length which when compiled produces an interesting pattern or function that is not always obvious from the code.