The PGM extension, short for Portable Graymap, is a graphic grayscale that has been encoded with 8 or 16 bits per pixel. It contains a grid of numbers that show different shades of gray. This information is commonly stored in an ASCII format. The header information in a PGM file defines the type of the PGM file (A P2 header stands for text and P5 for binary information), the dimensions of a picture and the maximum amount of different shades.
Mime type: image/x-portable-graymap, image/x-pgm