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:

• GIF version 87a and 89a [GIF87a, GIF89a]

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 "Restor 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.