GIF, the Graphics Interchange Format, was introduced by CompuServe in 1987 as a compact, hardware-independent way to transmit and store raster images across its online service. The format was revised in 1989 to the version known as GIF89a, whose specification is preserved at w3.org. The specification document identifies itself as “GRAPHICS INTERCHANGE FORMAT(sm) Version 89a” copyright CompuServe Incorporated of Columbus, Ohio, dated July 31, 1990, and describes itself as the programming reference defining the protocol for transmitting and storing raster graphic data in a hardware-independent manner.
A GIF image is palette-indexed: rather than storing a color value for every pixel, the file defines a color table of up to 256 entries and stores an index into that table for each pixel. This makes GIF excellent for graphics with limited color palettes, such as logos, icons, and line art, but poorly suited to photographs, where 256 colors cannot capture continuous tone. GIF89a added two features that defined its later cultural role: transparency, allowing one palette entry to be designated as see-through, and the ability to store multiple images in one file along with timing and looping control, which is the basis of the animated GIF.
The pixel data is compressed with LZW (Lempel-Ziv-Welch), a dictionary-based lossless algorithm. LZW was covered by US Patent 4,558,302, “High speed data compression and decompression apparatus and method,” invented by Terry A. Welch, granted December 10, 1985, and assigned originally to Sperry Corporation and later to Unisys. The patent describes an adaptive dictionary scheme that parses the input into strings and emits code signals for the longest stored matches, building on the earlier Lempel-Ziv work.
For years the patent attracted little attention from software developers using GIF, but in late 1994 Unisys and CompuServe announced licensing terms requiring royalties from developers of software that wrote GIF files. The announcement caused widespread anger across the early web and free-software communities, where GIF had become ubiquitous, and it directly motivated the creation of PNG as a patent-free replacement. The relevant LZW patents eventually expired around 2003 and 2004 in the United States and other jurisdictions, removing the legal cloud but only after PNG had established itself.
Despite its technical limitations and the patent saga, GIF proved remarkably durable. Its animation capability, present since GIF89a, found a second life as a core medium of internet culture, with short looping clips becoming a standard form of online expression long after the format’s compression and color limits had been surpassed by JPEG for photographs and PNG for graphics. GIF remains one of the longest-lived image formats on the web, a status owed less to its engineering than to the expressive niche its animation feature happened to fill.