PNM is a uncompressed file used for storing raster images. PNM image format can handle monochrome, color, and greyscale images. PNM files can store bitmaps in PBM, PGM, and PPM formats.

PNM image format is typically used for exchanging data between various image editors. PBM is a monochrome format (1 bit per pixel), PGM is greyscale (8 bits per pixel), and PPM is a RGB format that uses ASCII binary encoding (48 bits or 24 bits).