GIF

GIF (Graphics Interchange Format) is a bitmap image format for pictures that use 256 (or fewer) distinct colors (though there is a workaround for this limitation). and animations that use 256 (or fewer) distinct colors per frame. GIFs are compressed files, and are employed specifically to reduce the amount of time it takes to transfer images over a network connection. The format was introduced by CompuServe in 1987 and has since come into widespread usage on the World Wide Web.

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 modems.

Related Topics:
1987 - CompuServe - LZW - Data compression - Run-length encoding - PCX - MacPaint - Modem

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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 bytes of the file, which, when interpreted as ASCII, read "GIF87a" and "GIF89a", respectively.

Related Topics:
1989 - Bytes - ASCII

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When the World Wide Web gained popularity, GIF became one of the two image formats commonly used on Web sites, the other being the black and white XBM. JPEG came later with the mosaic browser and truecolor displays.

Related Topics:
XBM - JPEG

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The GIF89a feature of storing multiple images in one file, accompanied by control data, is used extensively on the web to produce simple 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.

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GIF images are limited to 256 colours, though it is possible to hack around this limitation, under certain circumstances, using the animation feature (see colour).

Related Topics:
Hack - Colour

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