The GEM format is used by applications such as Ventura Publisher, GEM Draw, GEM Scan, and GEM Paint. On the Atari ST where GEM is the standard operating environment, most graphical applications support this format.
The default extension for GEM files is IMG
Supporting Platforms and Applications
GEM, MS-DOS, Atari ST.
PMView supports both new and old type GEM files. Old type files supported are either 1 bit/pixel black & white, 2..4 bit/pixel color (EGA color map),or 8 bit grayscale. New type files can be 1..8 bit/pixel grayscale or 24-bit color. Note that 24-bit color images require Ventura 4.0. If you're going to import the image into an earlier version of Ventura you must convert the image to black & white or grayscale before saving it.