JPEG

JPEG (/ˈdʒeɪpɛɡ/ JAY-peg) is a commonly used method of lossy compression for digital images, particularly for those images produced by digital photography. The degree of compression can be adjusted, allowing a selectable tradeoff between storage size and image quality. JPEG typically achieves 10:1 compression with little perceptible loss in image quality. JPEG is the most widely used image compression standard on the internet. JPEG compression is used in a number of image file formats. JPEG/Exif is the most common image format used by digital cameras and other photographic image capture devices; along with JPEG/JFIF, it is the most common format for storing and transmitting photographic images on the World Wide Web. These format variations are often not distinguished, and are simply called JPEG. The term 'JPEG' is an initialism/acronym for the Joint Photographic Experts Group, which created the standard. The main basis for JPEG is the discrete cosine transform (DCT), a lossy compression method pioneered by Nasir Ahmed, T. Natarajan, K. R. Rao in 1974. The MIME media type for JPEG is image/jpeg, except in older Internet Explorer versions, which provides a MIME type of image/pjpeg when uploading JPEG images. JPEG files usually have a filename extension of .jpg or .jpeg. JPEG/JFIF supports a maximum image size of 65,535×65,535 pixels, hence up to 4 gigapixels for an aspect ratio of 1:1. The original JPEG specification published in 1992 implements processes from a number of research papers and patents cited by the CCITT and Joint Photographic Experts Group. The discrete cosine transform (DCT), the main basis for JPEG's lossy compression algorithm, was pioneered by Nasir Ahmed, T. Natarajan, and K. R. Rao in 1974. Their seminal 1974 paper is cited in the JPEG specification, along with several later research papers that did further work on DCT, including a 1977 paper by Wen-Hsiung Chen, C.H. Smith and S.C. Fralick that presented a fast DCT algorithm, as well as a 1978 paper by N.J. Narasinha and S.C. Fralick, and a 1984 paper by B.G. Lee. The specification also cites a 1984 paper by Wen-Hsiung Chen and W.K. Pratt as an influence on its quantization algorithm, and David A. Huffman's 1952 paper for its Huffman coding algorithm. The JPEG specification cites patents from several companies. The following patents provided the basis for its arithmetic coding algorithm. The JPEG specification also cites three other patents from IBM. Other companies cited as patent holders include AT&T (two patents) and Canon Inc. Absent from the list is U.S. Patent 4,698,672, filed by Compression Labs' Wen-Hsiung Chen and Daniel J. Klenke in October 1986. The patent describes a DCT-based image compression algorithm, and would later be a cause of controversy in 2002 (see Patent controversy below). However, the JPEG specification did cite two earlier research papers by Wen-Hsiung Chen, published in 1977 and 1984. 'JPEG' stands for Joint Photographic Experts Group, the name of the committee that created the JPEG standard and also other still picture coding standards. The 'Joint' stood for ISO TC97 WG8 and CCITT SGVIII. In 1987, ISO TC 97 became ISO/IEC JTC1 and, in 1992, CCITT became ITU-T. Currently on the JTC1 side, JPEG is one of two sub-groups of ISO/IEC Joint Technical Committee 1, Subcommittee 29, Working Group 1 (ISO/IEC JTC 1/SC 29/WG 1) – titled as Coding of still pictures. On the ITU-T side, ITU-T SG16 is the respective body. The original JPEG Group was organized in 1986, issuing the first JPEG standard in 1992, which was approved in September 1992 as ITU-T Recommendation T.81 and, in 1994, as ISO/IEC 10918-1.