Web Graphics

GIF (Graphics Interchange Format) is an 8-bit-per-pixel bitmap image format using a palette of up to 256 distinct colors from the 24-bit RGB color space. more...

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The format was introduced by CompuServe in 1987 and has since come into widespread usage on the World Wide Web due to its wide support and portability. It also supports animations and even allows a separate palette of 256 colors for each frame.

A GIF image employs lossless data compression so that the file size of an image may be reduced without degrading the visual quality, provided the image can be rendered with only 256 colours. (However, there is a hack that can overcome this limitation under certain circumstances; see true colour.) This limitation makes the GIF format unsuitable for color photographs (which are more commonly seen in the JPEG format) and other images with continuous color, but well-suited for more simple images such as graphics or logos with solid areas of color. Monochrome photographs can be represented well as GIFs but still suffer from file size bloat due to the inappropriate compression technique.

Many software developers were surprised when it was revealed that the compression algorithm used by GIF had been patented by Unisys, and that they would have to pay royalties for writing programs that generated 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.

The Software Freedom Law Center had stated that since 1 October 2006, there are no significant patent claims interfering with employment of the GIF format.

Although the original GIF and related patents have expired, PNG is still touted as a technically superior alternative, and has become the third most common image format on the 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.

The original version of GIF was called 87a. In 1989, CompuServe devised an enhanced version, called 89a, 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.

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.

Read more at Wikipedia.org