N. Ahmed

Nasir Ahmed (born 1940) is an American electrical engineer and computer scientist. He is Professor Emeritus of Electrical and Computer Engineering at University of New Mexico (UNM). He is best known for inventing the discrete cosine transform (DCT) in the early 1970s. The DCT is the most widely used data compression transformation, the basis for most digital media standards (image, video and audio) and commonly used in digital signal processing. He also described the discrete sine transform (DST), which is related to the DCT.

Discrete cosine transform (DCT)

The discrete cosine transform (DCT) is a lossy compression algorithm that was first conceived by Ahmed while working at the Kansas State University, and he proposed the technique to the National Science Foundation in 1972. He originally intended the DCT for image compression. It described what is now called the type-II DCT (DCT-II), as well as its inverse, the type-III DCT (a.k.a. IDCT). Discrete Cosine Transform (with T. Natarajan and K. R. Rao), since its publication. The basic research work and events that led to the development of the DCT were summarized in a later publication by Ahmed entitled "How I came up with the Discrete Cosine Transform". It is a core component of the 1992 JPEG image compression technology developed by the JPEG Experts Group working group and standardized jointly by the ITU, ISO and IEC. A tutorial discussion of how it is used to achieve digital video compression in various international standards defined by ITU and MPEG (Moving Picture Experts Group) is available in a paper by K. R. Rao and J. J. Hwang which was published in 1996, and an overview was presented in two 2006 publications by Yao Wang. The image and video compression properties of the DCT resulted in its being an integral component of the following widely used international standard technologies:

Standard Technologies JPEG Storage and transmission of photographic images on the World Wide Web (JPEG/JFIF); and widely used in digital cameras and other photographic image capture devices (JPEG/Exif). MPEG-1 Video Video distribution on CD or via the World Wide Web. MPEG-2 Video (or H.262) Storage and handling of digital images in broadcast applications: digital TV, HDTV, cable, satellite, high speed internet; video distribution on DVD. H.261 First of a family of video coding standards (1988). Used primarily in older video conferencing and video telephone products. H.263 Videotelephony and videoconferencing

The form of DCT used in signal compression applications is sometimes referred to as DCT-2 in the context of a family of discrete cosine transforms, or as DCT-II.

More recent standards have used integer-based transforms that have similar properties to the DCT but are explicitly based on integer processing rather than being defined by trigonometric functions. As a result of these transforms having similar symmetry properties to the DCT and being, to some degree, approximations of the DCT, they have sometimes been called "integer DCT" transforms. Such transforms are used for video compression in the following technologies pertaining to more recent standards. The "integer DCT" designs are conceptually similar to the conventional DCT but are simplified to provide exactly specified decoding with reduced computational complexity.

Standard Technologies VC-1 Windows media video 9, SMPTE 421. H.264/MPEG-4 AVC The most commonly used format for recording, compression and distribution of high definition video; streaming internet video; Blu-ray Discs; HDTV broadcasts (terrestrial, cable and satellite). H.265/HEVC Successor to the H.264/MPEG-4 AVC standard having substantially improved compression capability. H.266/VVC Successor to HEVC having substantially improved compression capability. WebP Images A graphic format that supports the lossy compression of digital images. Developed by Google. WebM Video A multimedia open source format intended to be used with HTML5. Developed by Google.

A DCT variant, the modified discrete cosine transform (MDCT), is used in modern audio compression formats such as MP3, Advanced Audio Coding (AAC), and Vorbis (OGG).

The discrete sine transform (DST) is derived from the DCT, by replacing the Neumann condition at x=0 with a Dirichlet condition.

Background Alumnus of the Bishop Cotton Boys' School; received his B.S. degree in electrical engineering from the University of Visvesvaraya College of Engineering, Bangalore in 1961; Received his M.S. and Ph.D. degrees in electrical and computer engineering from the University of New Mexico in 1963 and 1966, respectively. His doctoral dissertation adviser was Shlomo Karni; Principal research engineer, Honeywell, St. Paul, Minnesota, from 1966 to 1968; Professor, Electrical and Computer Engineering Department, Kansas State University, 1968–83; 1983-2001: University of New Mexico—Presidential Professor of Electrical and Computer Engineering, 1983–89; chair, Department of Electrical and Computer Engineering, 1989–94; dean of engineering, 1994–96; associate provost for research and dean of graduate studies, 1996–2001; Consultant, Sandia National Laboratories, Albuquerque, New Mexico, 1976–90. Married to Esther Parente-Ahmed. Son, Michael Ahmed Parente.

Books

Popular culture

In season 5, episode 8 of NBC's This Is Us, Ahmed's story was told to highlight the importance of image and video transmission over the Internet in modern society, particularly during the COVID-19 pandemic. The episode ends with a picture of Ahmed and his wife, along with captions explaining the importance of his work, and that producers spoke to the couple over video chat to understand their story and incorporate it into the episode.