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[[Image:Rotating earth (small).gif|right|frame|A rotating globe in GIF format]]
'''GIF''' (Graphics Interchange Format) is a [[bitmap]] [[Graphics file formats|image format]] for pictures and [[animation]]s that
A GIF file employs [[lossless data compression]] so that the size of an image may be reduced, but without degrading the visual quality. The popular [[JPEG|JPEG (Joint Photographic Experts Group)]] format generates even smaller files than GIF and supports images with more than 16 million different colours, but will always [[lossy data compression|lose some of the detail]]s in a picture. The nature of this loss has been minimized for typical [[digital photography|digital photographs]] — but the appearance of logos, buttons, and icons generally suffer when they are encoded as JPEGs. This leads web designers to choose the GIF format for these elements.
The format was introduced in [[1987]] by [[CompuServe]] in order to provide a colour image format for their file downloading areas, replacing their earlier RLE format which was black and white only. GIF became popular because it used [[LZW]] [[data compression]], which was more efficient than the [[run-length encoding]] that formats such as [[PCX]] and [[MacPaint]] used, and fairly large images could therefore be downloaded in a reasonable amount of time, even with very slow [[modem]]s. ▼
Many software developers were caught by surprise when it was revealed that 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|PNG (Progressive Network Graphics)]] standard. Although the Unisys patent has since expired, PNG is still touted as a technically superior alternative, and has become the third most common image format on the web.
GIF images are limited to 256 colours, though it is possible to [[hack (technology slang)|hack]] around this limitation, under certain circumstances, using the animation feature (see [[#truecolour|colour]]).▼
English speakers often pronounce "GIF" with either an affricate as in "giraffe" /dʒɪf/ or a plosive as in "gift" /gɪf/. The format's creators are quoted as using an affricate to pronounce the acronym. There is plenty of evidence to suggest this, much of which can be found [http://www.olsenhome.com/gif/ here]. However, many people use the plosive pronunciation in daily conversation. The affricate was used as the developers had a sense of humour "Choosy Developers Choose GIF", making a play on a then-famous commercial for peanut butter. Outside of the English language there are a number of further variants.▼
==History==
▲The GIF format was introduced in [[1987]] by [[CompuServe]] in order to provide a colour image format for their file downloading areas, replacing their earlier RLE format which was black and white only. GIF became popular because it used [[LZW]] [[data compression]], which was more efficient than the [[run-length encoding]] that formats such as [[PCX]] and [[MacPaint]] used, and fairly large images could therefore be downloaded in a reasonable amount of time, even with very slow [[modem]]s.
The original version of GIF was 87a. In [[1989]], CompuServe devised an enhanced version, called 89a [http://www.w3.org/Graphics/GIF/spec-gif89a.txt], that added support for multiple images in a stream, interlacing and storage of application-specific metadata. The two versions can be distinguished by looking at the first six [[byte|bytes]] of the file, which, when interpreted as [[ASCII]], read "GIF87a" and "GIF89a", respectively.▼
▲The original version of GIF was called 87a. In [[1989]], CompuServe devised an enhanced version, called 89a [http://www.w3.org/Graphics/GIF/spec-gif89a.txt], that added support for multiple images in a stream, interlacing and storage of application-specific metadata. The two versions can be distinguished by looking at the first six [[byte|bytes]] of the file, which, when interpreted as [[ASCII]], read "GIF87a" and "GIF89a", respectively.
When the World Wide Web gained popularity, GIF became one of the two image formats commonly used on Web sites, the other being [[JPEG]]. Most internet browsers at this time did not support any other image formats, not even uncompressed [[Windows bitmap]] files, to discourage web designers from using files larger than necessary.
The GIF89a feature of storing multiple images in one file, accompanied by control data, is used extensively on the web to produce simple [[computer animation|animations]]. The optional interlacing feature, which stored image scanlines out of order in such a fashion that even a partially downloaded image was somewhat recognizable, also helped GIF's popularity, as a user could abort the download if it was not what was required.
▲GIF images are limited to 256 colours, though it is possible to [[hack (technology slang)|hack]] around this limitation, under certain circumstances, using the animation feature (see [[#truecolour|colour]]).
==Pronunication==
▲English speakers often pronounce "GIF" with either an affricate as in "giraffe" /dʒɪf/ or a plosive as in "gift" /gɪf/. The format's creators are quoted as using an affricate to pronounce the acronym. There is plenty of evidence to suggest this, much of which can be found [http://www.olsenhome.com/gif/ here]. However, many people use the plosive pronunciation in daily conversation. The affricate was used as the developers had a sense of humour "Choosy Developers Choose GIF", making a play on a then-famous commercial for peanut butter. Outside of the English language there are a number of further variants.
==Unisys and LZW patent enforcement==
[[Image:Burn All GIFs.png|frame|One of the [http://burnallgifs.org/archives/images/ "Burn All GIFs" graphics] ]]
The LZW compression algorithm on which GIF is based, was covered by {{US patent|4,558,302}} owned by [[Unisys Corporation|Unisys]]. When Compuserve first developed the GIF they did not know that LZW was covered by a [[patent]]. In December [[1994]], after Unisys discovered that GIF used the LZW, they announced that they would be seeking royalties on that patent; all commercial programs capable of producing GIF files would be required to pay a license fee to Unisys.
By this time, GIF was in such widespread use that most companies producing these programs had little choice but to pay. In late August 1999, Unisys terminated its royalty-free LZW technology licenses for free software and non-commercial proprietary software and even for individual users of unlicensed programs, prompting the [[League for Programming Freedom]] to launch the Burn All GIFs campaign to inform the public of the alternatives.
On [[June 20]], [[2003]], the United States patent on the LZW algorithm expired [http://www.unisys.com/about__unisys/lzw], which means that Unisys and Compuserve can no longer collect royalties for use of the GIF format in that country. Those bothered with the patent enforcement dubbed this day GIF Liberation Day. The equivalent patents in Europe and Japan expired on [[June 18]] and [[June 20]] [[2004]] respectively, with the Canada patent following on [[July 7]].
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