<?xml version="1.0" encoding="utf-8"?>
<PRONOM-Report xmlns="http://pronom.nationalarchives.gov.uk">
  <report_format_detail>
    <FileFormat>
      <FormatID>223</FormatID>
      <FormatName>GEM Image</FormatName>
      <FormatVersion>
      </FormatVersion>
      <FormatAliases>
      </FormatAliases>
      <FormatFamilies>
      </FormatFamilies>
      <FormatTypes>Image (Raster)</FormatTypes>
      <FormatDisclosure>
      </FormatDisclosure>
      <FormatDescription>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.</FormatDescription>
      <BinaryFileFormat>Text</BinaryFileFormat>
      <ByteOrders>Big-endian (Motorola)</ByteOrders>
      <ReleaseDate>
      </ReleaseDate>
      <WithdrawnDate>
      </WithdrawnDate>
      <ProvenanceSourceID>1</ProvenanceSourceID>
      <ProvenanceName>Digital Preservation Department / The National Archives</ProvenanceName>
      <ProvenanceSourceDate>02 Aug 2005</ProvenanceSourceDate>
      <ProvenanceDescription>
      </ProvenanceDescription>
      <LastUpdatedDate>29 Mar 2022</LastUpdatedDate>
      <FormatNote>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</FormatNote>
      <FormatRisk>
      </FormatRisk>
      <TechnicalEnvironment>
      </TechnicalEnvironment>
      <FileFormatIdentifier>
        <Identifier>x-fmt/159</Identifier>
        <IdentifierType>PUID</IdentifierType>
      </FileFormatIdentifier>
      <ExternalSignature>
        <ExternalSignatureID>217</ExternalSignatureID>
        <Signature>img</Signature>
        <SignatureType>File extension</SignatureType>
      </ExternalSignature>
      <InternalSignature>
        <SignatureID>397</SignatureID>
        <SignatureName>GEM Paint Image</SignatureName>
        <SignatureNote>2 byte Version (always 1), number of words in header (8), 2 byte number of planes (1 or 4), pattern size (2)</SignatureNote>
        <ByteSequence>
          <ByteSequenceID>503</ByteSequenceID>
          <PositionType>Absolute from BOF</PositionType>
          <Offset>0</Offset>
          <MaxOffset>
          </MaxOffset>
          <IndirectOffsetLocation>
          </IndirectOffsetLocation>
          <IndirectOffsetLength>
          </IndirectOffsetLength>
          <Endianness>Big-endian</Endianness>
          <ByteSequenceValue>0001000800(01|04)0002</ByteSequenceValue>
        </ByteSequence>
      </InternalSignature>
      <RelatedFormat>
        <RelationshipType>Is previous version of</RelationshipType>
        <RelatedFormatID>2484</RelatedFormatID>
        <RelatedFormatName>XIMG (Extended GEM Bit Image)</RelatedFormatName>
        <RelatedFormatVersion>
        </RelatedFormatVersion>
      </RelatedFormat>
    </FileFormat>
    <SearchCriteria>Criteria</SearchCriteria>
  </report_format_detail>
</PRONOM-Report>
