GIF-hul Module

1 Introduction

The GIF-hul module recognizes and validates the GIF (Tagged Interchange Format) format [GIF89a].

The module is invoked by the:

jhove ... -m gif-hul ...

command line option.

2 Coverage

The GIF-hul module recognizes and validates the following public profiles:

3 Well-Formedness

The following criteria must be met by a GIF object for JHOVE to consider it well-formed:

  • Properly formed signature (“GIF” at byte offset 0) and version identifier (“87a” or “89a” at byte offset 3)
  • A sequence of properly formed (as defined by the relevant specifications) control, graphic-rendering, and special purpose blocks
  • GIF terminator (0x00) at end of the content stream

4 Validity

The following criteria must be met by a GIF file for JHOVE to consider it valid:

  • The file is well-formed
  • At most one global color map
  • At most one graphic control extension preceding an image descriptor or a plain text extension

5 Representation Information

The MIME type is reported as: image/gif

In addition to the standard JHOVE representation information, the following GIF-specific properties are reported:

  • Property “GIFMetadata” of type PROPERTY and arity ARRAY
    • Property “GraphicRenderingBlocks” of type INTEGER and arity SCALAR
      indicating the total number of Image Descriptor and Plain Text Extension blocks

    • Property “Blocks” of type PROPERTY and arity LIST
      The block types are “LogicalScreenDescriptor”, “GlobalColorTable”, “GraphicControlExtension”, “ImageDescriptor”, “PlainTextExtension”, “ApplicationExtension”, “CommentExtension”

      • Property “LogicalScreenDescriptor” of type PROPERTY and arity ARRAY
        • Property “LogicalScreenWidth” of type INTEGER and arity SCALAR
        • Property “LogicalScreenHeight” of type INTEGER and arity SCALAR
        • Property “ColorResolution” of type SHORT and arity SCALAR
        • Property “BackgroundColorIndex” of type SHORT and arity SCALAR
        • Property “PixelAspectRatio” of type SHORT and arity SCALAR
        • Property “GlobalColorTableFlag” of type BYTE and arity SCALAR
          =0 “No global color table; background color index meaningless”;
          =1 “Global color table follows; background color index meaningful”
        • Property “GlobalColorTableSortFlag” of type BYTE and arity SCALAR
          =0 “Not ordered”;
          =1 “Ordered by decreasing importance”
        • Property “GlobalColorTableSize” of type SHORT and arity SCALAR

      • (Optional) property “GlobalColorTable” of type SHORT and arity ARRAY

      • (Optional) property “GraphicControlExtension” of type PROPERTY and arity ARRAY
        • Property “DisposalMethod” of type BYTE and arity SCALAR
          =0 “No disposal specified”; =1 “Do not dispose”; =2 “Restore to background color”; =3 “Restore to previous”
        • Property “UserInputFlag” of type BYTE and arity SCALAR
          =0 “User input not expected”; =1 “User input expected”
        • Property “TransparencyFlag” of type BYTE and arity SCALAR
          =0 “Transparent index is not given”; =1 “Transparent index given”
        • Property “DelayTime” of type INTEGER and arity SCALAR
        • Property “TransparentColorIndex” of type SHORT and arity SCALAR
      • (Optional) property “ImageDescriptor” of type PROPERTY and arity ARRAY
        • Property “ImageLeftPosition” of type INTEGER and arity SCALAR
        • Property “ImageRightPosition” of type INTEGER and arity SCALAR
        • Property “InterlaceFlag” of type BYTE and arity SCALAR
          =0 “Image is not interlaced”; =1 “Image is interlaced”
        • Property “LocalColorTableFlag” of type BYTE and arity SCALAR
          =0 “No local color table; use global table if available”;
          =1 “Local color table follows”
        • Property “LocalColorTableSortFlag” of type BYTE and arity SCALAR
          =0 “Not ordered”; =1 “Order by decreasing importance”

        • Property “LocalColorTableSize” of type SHORT and arity SCALAR

        • Property “NisoImageMetadata” of type NISOIMAGEMETADATA and arity SCALAR
          MIMEType = “image/gif”;
          ByteOrder = “little_endian”;
          CompressionScheme = 5 “LZW”;
          ColorSpace = 3 “Palette color”;
          Orientation = 1 “Normal”;
          ImageWidth = ImageWidth; ImageLength = ImageHeight;
          SamplesPerPixel = 1;
          ColorMap = local color table (if supplied)
      • (Optional) property “PlainTextExtension” of type PROPERTY and arity ARRAY
        • Property “TextGridLeftPosition” of type INTEGER and type SCALAR
        • Property “TextGridTopPosition” of type INTEGER and type SCALAR
        • Property “TextGridWidth” of type INTEGER and type SCALAR
        • Property “TextGridHeight” of type INTEGER and type SCALAR
        • Property “CharacterCellWidth” of type SHORT and type SCALAR
        • Property “CharacterCellHeight” of type SHORT and type SCALAR
        • Property “TextForegroundColorIndex” of type SHORT and type SCALAR
        • Property “TextBackgroundColorIndex” of type SHORT and type SCALAR
        • Property “PlainTextData” of type STRING and type SCALAR
      • (Optional) property “ApplicationExtension” of type PROPERTY and arity ARRAY
        • Property “ApplicationIdentifier” of type STRING and arity SCALAR
        • Property “ApplicationAuthenticationCode” of type SHORT and type ARRAY
        • Property “ApplicationDataSize” of type INTEGER and type SCALAR
          use the block size to determine the length of the application data
      • (Optional) property “CommentExtension” of type STRING and arity SCALAR

Image technical properties are reported in terms of the NISO Z39.87 data dictionary.

5.1 Profiles

  • GIF 87a
    The presence of the version identifier “87a” indicates version 87a.
  • GIF 89a
    The presence of the version identifier “89a” indicates version 89a.

6 Additional Module Properties

  • Nominal file extension: .gif

Note “GIF” and “Graphics Interchange Format” are trademarks of CompuServe Interactive Services, Inc.