Nasir Ahmed  

Born  1940 
Nationality  
Education  
Known for 

Spouse  Esther ParenteAhmed 
Children  Michael Ahmed Parente 
Awards 

Scientific career  
Fields  
Thesis  
Doctoral advisor  Shlomo Karni 
Nasir Ahmed (born 1940) is an IndianAmerican 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.^{[1]}
Further information: Discrete cosine transform 
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.^{[2]}^{[3]} Ahmed developed a working DCT algorithm with his PhD student T. Natarajan and friend K. R. Rao in 1973,^{[2]} and they presented their results in a January 1974 paper.^{[4]}^{[5]}^{[6]} It described what is now called the typeII DCT (DCTII),^{[7]}^{: 51 } as well as its inverse, the typeIII DCT (a.k.a. IDCT).^{[4]}
Ahmed was the leading author of the benchmark publication,^{[8]}^{[9]} Discrete Cosine Transform (with T. Natarajan and K. R. Rao),^{[4]} which has been cited as a fundamental development in many works^{[10]} 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".^{[2]}
The DCT is widely used for digital image compression.^{[11]}^{[12]}^{[13]} It is a core component of the 1992 JPEG image compression technology developed by the JPEG Experts Group^{[14]} working group and standardized jointly by the ITU,^{[15]} 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^{[16]}^{: JPEG: Chapter 8; H.261: Chapter 9; MPEG1: Chapter 10; MPEG2: Chapter 11 } which was published in 1996, and an overview was presented in two 2006 publications by Yao Wang.^{[17]}^{[18]} 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). 
MPEG1 Video  Video distribution on CD or via the World Wide Web. 
MPEG2 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 DCT2 in the context of a family of discrete cosine transforms,^{[19]} or as DCTII.
More recent standards have used integerbased transforms that have similar properties to the DCT but are explicitly based on integer processing rather than being defined by trigonometric functions.^{[20]} 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 

VC1  Windows media video 9, SMPTE 421. 
H.264/MPEG4 AVC  The most commonly used format for recording, compression and distribution of high definition video; streaming internet video; Bluray Discs; HDTV broadcasts (terrestrial, cable and satellite). 
H.265/HEVC  Successor to the H.264/MPEG4 AVC standard having substantially improved compression capability. 
H.266/VVC  Successor to HEVC having substantially improved compression capability. 
WebP Images  A graphic format that support 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,^{[21]} 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.^{[7]}^{: 35 } The DST was described in the 1974 paper by Ahmed, Natarajan and Rao.^{[4]}
Ahmed later was involved in the development a DCT lossless compression algorithm with Giridhar Mandyam and Neeraj Magotra at the University of New Mexico in 1995. This allows the DCT technique to be used for lossless compression of images. It is a modification of the original DCT algorithm, and incorporates elements of inverse DCT and delta modulation. It is a more effective lossless compression algorithm than entropy coding.^{[22]}
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 COVID19 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.^{[23]}