| Description |
The GEM raster format (also known as GEM VDI Bit Image; GEM Bit Image; GEM Image; GEM Bitmap; or IMG) is an image format native to the Graphical Environment Manager (GEM) operating system and developed at Digital Research. The format was used by GEM Paint and Ventura Publisher, and by a variety of Atari ST software.
GEM raster images may be color, gray scale, or black and white and are always read and written in the big-endian format. The format of bi-level images is well standardized, but the specification is ambiguous as to the format of color images. As a result, other color formats of GEM raster image were later developed, some of which have their own names, such as XIMG (Extended GEM Bit Image), TIMG (TrueColor IMG), STTT, or Hyperpaint. |
Details: File format summary
: detailed report on file format 
Digital Preservation Department / The National Archives
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