Format

GEM Image

Summary

Name: GEM Image
Identifiers: PUID: x-fmt/159
Format type: Image (Raster)
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.
Note: http://fileformats.archiveteam.org/wiki/GEM_Raster https://www.wikidata.org/wiki/Q28206162 https://www.seasip.info/Gem/ff_img.html https://www.fileformat.info/format/gemraster/spec/20e311cc16f844fda91beb539d62c46c/view.htm https://archive.org/stream/mac_Graphics_File_Formats_Second_Edition_1996/Graphics_File_Formats_Second_Edition_1996_djvu.txt
File extensions: img
Source: Digital Preservation Department / The National Archives

Is previous version of

Note: 2 byte Version (always 1), number of words in header (8), 2 byte number of planes (1 or 4), pattern size (2)