GIF (Graphics Interchange Format) / GIFF (Graphics Interchange File Format) is a bitmap image format for pictures with up to 256 distinct colours from the over 16 million representable in 24 bit rgb. The format was introduced by CompuServe in 1987 and has since come into widespread usage on the World Wide Web. GIFs are compressed files, which reduces the amount of time it takes to transfer images over a network connection.

A GIF file employs lossless data compression so that the file size of an image may be reduced without degrading the visual quality, provided the image fits into 256 colours. (However, there is a hack that can overcome this limitation under certain circumstances; see True Color.) The GIF format's 256-colour limitation makes it unsuitable for photographs, though losslessly compressed photographs tend to be unacceptably large for the web anyway. On the other hand the lossy JPEG format does poorly on sharp transitions like those in diagrams or text, producing highly visible artifacts and little file-size reduction. Therefore GIF is normally used for diagrams, buttons, etc., that have a small number of colours, while the JPEG format is used for photographs.

Many software developers were caught by surprise when it was revealed that the compression algorithm used by the GIF format had been patented by Unisys, and that they would have to pay royalties for writing programs that generated (or displayed) GIF files. The desire for a comparable format with fewer legal restrictions (as well as fewer technical restrictions such as the number of colours) led to the development of the PNG (Portable Network Graphics) standard. Although the Unisys gif patents have expired and the IBM ones will expire in the near future, PNG is still touted as a technically superior alternative, and has become the third most common image format on the web. The latest expiration date of the GIF-related patents will most probably be Friday, August 11, 2006 ^*.

More on [ GIF ]

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