GIF File Format
   
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    GraphicsAcademy.com  >  File Formats  >  Graphics Interchange Format

       

     

    GIF File Format

    Short Name GIF
    Long Name Graphics Interchange Format
    Typical File Extensions .gif
    Contains Bitmaps/Animation
    This is a format developed by CompuServe Inc. for storing bitmaps.

    GIF files can contain bitmaps at a variety of color depths: 2, 4, 16, or 256 color, in each case with a palette.

    The GIF format has between through two revisions (87a and 89a), and the newer revision (89a) is a superset of the older version (87a). Modern GIF-compatible software, should therefore have no problem reading files of either revision.

    The 89a revision of GIF supports transparency, interlacing, and simple animation whereby multiple images within a single GIF file can be displayed in a timed or looped sequence.

    GIF files are compressed using an LZW compression scheme, which attracted a large amount of controversy when Unisys announced this algorithm was patented, and charged license fees for software developers using this algorithm. However, according to The GIF Controversy: A Software Developer's Perspective, these patents have now expired as of 20 June 2004.

    As a result of the controversy resulting for the patent claims around this format, software developers took a number of steps:
    1. The PNG format was developed as a replacement for GIF. However, while the PNG format is increasingly popular, it has not really replaced GIF which is still widely used.

    2. Some software developers tried to devise methods of encoding GIFs which would not infringe on the Unisys patent (see, for example, DaubNET: File Formats Collection: GIF):

      • The alternative encoding methods, result in larger file sizes as they are not as well compressed as LZW.

      • Files encoded (saved) using the alternative encoding methods, can be read by any GIF reading software.

      • As far as I know, it was not possible to write software able to decode all GIF files, without stepping into the territory covered by the Unisys patent.
    A technical discussion of this format can be found in Chapter 7 of Graphics File Formats by David C. Kay and John R. Levine.

    Please Note:
    • We are not lawyers. This web site is not intended as legal advice, and should not be construed as such. Please consult an attorney should you require legal advice on copyrights, patents or any other matter.

    • GIF and 'Graphics Interchange Format' are trademarks of CompuServe Inc..

    • Unisys held patents on the LZW compression scheme, which according to The GIF Controversy: A Software Developer's Perspective these patents expired as of 20 June 2004.



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