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Back to Web Providers... SOME DEFINITIONS

GIF. Graphics Interchange Format. A very widely used raster image format developed by Compuserve in 1987 and enhanced in 1989. It uses an indexed color palette limited to 256 colors and supports transparent images and simple animation.

JPEG. Joint Photographic Experts Group. A very widely used raster image format that supports several levels of data compression. All JPEG compression is lossy – some image details are lost and the more the image is compressed, the more details are lost. (Strictly speaking JPEG is just the compression algorithms. The file format is formally JFIF – JPEG File Interchange Format – but JPEG is generally used to refer the file format as well.)

LZW. A lossless compression scheme used in GIF images, some TIFF images (TIFF supports other compression methods as well), and other file formats. It was devised by Terry Welch, based in part on work by A. Lempel and J. Ziv. It was patented in 1985 (U.S. patent 4,558,302) and the patent ended up held by Unisys. The U.S. patent expired 20 June 2003.

PDF. Portable Document Format. A file format created by Adobe Systems Inc. and supported by their free Acrobat Reader. It is widely used to represent print documents on the web.

PNG. Portable Network Graphics. A raster image format designed for web applications and supported by newer web browsers. It provides a variety of compression schemes and other features. See http://www.w3.org/Graphics/PNG/.

SVG. Scalable Vector Graphics. A language for describing two-dimensional graphics in XML designed to support web applications. Support is becoming more widespread. See http://www.w3.org/Graphics/SVG/.

TIFF. Tag Image File Format. A raster image format that includes several color depths, compression methods, and other features. There are a number of specialized variants. It was first published by Aldus Corporation in 1986 and most recently by Adobe Systems Inc.


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