Joan Laverne Mitchell (May 24, 1947 – December 2, 2015)^[1][2] was an American computer scientist, data compression pioneer, and inventor who, as a researcher at IBM, co-invented the JPEG digital image format.^[3]

Mitchell was born on May 24, 1947, in Modesto, California. Mitchell's father was William Mitchell and her mother was Doris Mitchell. ^[2]

Mitchell was a National Merit Scholar at Stanford University, where her work included an independent study project on Brillouin scattering in bromine.^[1] In 1969, Mitchell graduated with a Bachelor of Science degree in physics from Stanford University^[1][4] with distinction^[5] and Phi Beta Kappa.^[1] She followed in the footsteps of her grandmother, Eulalia Richardson Mitchell, who also earned Stanford physics degrees in 1910 and 1912.^[1][6]

Mitchell went on to graduate study in condensed matter physics at the University of Illinois at Urbana–Champaign, and earned a master's degree in 1971 and a Ph.D. in 1974 there.^[1][3][4] As part of her Ph.D. work, she also learned computer programming, so that she could use a computer to solve the differential equations arising in her research.^[1] Her dissertation, Effect of heterovalent impurities co-diffusing with monovalent tracers in ionic crystals, was supervised by David Lazarus.^[7]

Mitchell began working at the IBM Thomas J. Watson Research Center in 1974, in the Exploratory Printing Technologies Group.^[3][4] There, her inventions included a method for ultrasonic printing, a method for thermal-transfer printing later used in some models of the IBM Selectric typewriter, data compression for fax machines, a teleconferencing system,^[3] and the Q-coder method for arithmetic coding used in JBIG image compression.^[1] From 1987 to 1994, Mitchell helped develop the JPEG standard, and she became a co-author with Bill Pennebaker of the first book on the standard.^[1][3][4] Gregory K. Wallace, another member of the group, remembers Mitchell and Pennebaker as "two of the most insightful, energetic, and prolific members" of the Joint Photographic Experts Group.^[8]

During the mid-1990s Mitchell moved from the Watson Research Center to a different IBM group in Vermont and then (after a short leave as a visiting professor at the University of Illinois) to IBM's Printing Systems Division in Colorado.^[3][4] In 2007 IBM sold their Printing Systems Division to Ricoh,^[9] and Mitchell went with them to the resulting joint venture, InfoPrint Solutions. She retired in 2009,^[10] and died on December 2, 2015.^[2]

Mitchell became an IEEE Fellow in 1999 "for contributions to the development of international image compression standards",^[11] an IBM Fellow in 2001,^[3][4] and, in 2004, a member of the National Academy of Engineering "for leadership in setting standards for the formation of photographic fax and image compression".^[1] She was the 2011 winner of the IEEE Masaru Ibuka Consumer Electronics Award,^[1][10] and is listed in the Hall of Fame of distinguished alumni of the University of Illinois at Urbana–Champaign.^[3]

Mitchell is the author of:

• JPEG: Still Image Data Compression Standard (with William B. Pennebaker, Van Nostrand Reinhold, 1992)^[12]
• MPEG Video Compression Standard (with William B. Pennebaker, Chad Fogg, and Didier J. LeGall, Chapman and Hall, 1997)^[13]
• Dr. Joan's Mentoring Book: Straight Talk about Taking Charge of Your Career (with Nancy Walker-Mitchell, 2007)^[1][10]