The PBM which is an acronym for Portable Bit-Map is a simple structured monochrome raster image format. It is actually part of Netpbm, an open-source package of graphics programs used in Unix operating systems.
Because of its simple and general design, it's easy to develop programs to convert, manipulate and create the image. The file contents could be either ASCII or binary defined in its simple always ASCII header information.
|Sending monochrome bitmap images over email back in the '80s.
|Jeffrey A. Poskanzer