Bede Liu, pioneer in digital signal processing and beloved mentor, dies at age 91

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Bede Liu, pioneer in digital signal processing and beloved mentor, dies at age 91

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By

Molly Sharlach, Office of Engineering Communications

on<br>June 24, 2026, 3:49 p.m.

Bede Liu, an emeritus professor of electrical engineering and a pioneer in digital signal processing, died on May 7. He was 91.<br>Liu’s pathbreaking research aided the transition from analog to digital processing of sound, images and video. Along with the 53 Ph.D. students he mentored, he developed methods of filtering and compressing digital signals to mitigate errors and dramatically reduce the computation needed for signal processing. These techniques have led to now-ubiquitous technologies for storing and streaming media.

Bede Liu

Photo by<br>David Kelly Crow for the Office of Engineering Communications

“He was a highly impactful scholar and teacher — always thinking ahead of future needs and changing technologies,” said colleague Peter Ramadge, the Gordon Y.S. Wu Professor of Engineering, Emeritus.<br>In the 1990s, Liu turned his attention to media integrity and copyright issues. He created techniques for digital watermarking — hidden signals that could identify a genuine copy of a song, image or video and prevent unauthorized distribution or tampering.<br>Lessons learned from Liu's work have guided industries in identifying suitable settings and applications for watermarking. For example, each copy of a Hollywood film given to a critic or theater now carries a unique forensic watermark to prevent unauthorized redistribution, said Min Wu, a 2001 Ph.D. alumna who worked on digital watermarking with Liu.<br>Former students and colleagues remembered Liu for his humility, humor and generosity. For Ken Steiglitz, the Eugene Higgins Professor of Computer Science, Emeritus, “cheer” is the word that first comes to mind when thinking of Liu. He was “always ready with a positive remark, a quick smile, or, maybe, some tips on the right way to cook a duck.”<br>Liu loved to organize dinners with colleagues and students at Chinese restaurants — both in the Princeton area and when traveling for conferences, said H. Vincent Poor, the Michael Henry Strater University Professor of Electrical and Computer Engineering.<br>“He would go in advance and talk to the chef about what to serve us — it wouldn’t be what was on the menu. Rather, it would be some kind of fabulous dishes that he knew of,” said Poor. “It was always fantastic to go out to dinner with him.”<br>Liu’s Ph.D. students went on to become leading figures in academia and industry. Among them are many professors at major universities, two deans of engineering, and several executives at companies such as IBM and Google.<br>Liu’s first Ph.D. student at Princeton, co-advised with professor John Thomas, was Robert Kahn. While working at the U.S. Defense Advanced Research Projects Agency (DARPA), Kahn created an early computer networking protocol that paved the way for the internet. Princeton honored him with the James Madison Medal in 2022. With his colleague Vinton Cerf, in 1997 Kahn was awarded the National Medal of Technology from President Bill Clinton.<br>“[Liu’s] former students were very successful, and I think that’s a testament to his skill as a mentor. But he also mentored the younger faculty,” said Poor, who earned his Ph.D. in electrical engineering at Princeton in 1977 (mentored by Thomas) and in 1990 became Liu’s colleague when he joined the Princeton faculty. Liu modeled the importance of continuing to support his students well beyond their graduation, said Poor.<br>Fred Mintzer, a self-described “working-class kid,” left his job at a phone company to pursue a Ph.D. with Liu in the 1970s. Liu enabled him to become “a successful researcher … with ambitions to do more than just behind-the-scenes work,” said Mintzer. His research with Liu “gave me a lot of confidence and encouraged me to follow my dreams,” said Mintzer, who retired from IBM after 35 years as a research manager and director.<br>An inspirational spirit of adventure<br>Liu inspired students and colleagues with his “spirit of adventure,” said Mintzer. At IBM, this spirit led Mintzer to take on ambitious, unconventional projects to digitize collections for the Vatican Library, the U.S. National Gallery of Art and Russia’s Hermitage Museum.<br>Mintzer is among 25 of Liu’s former Ph.D. students to be named fellows of the Institute of Electrical and Electronics Engineers (IEEE) — a high honor bestowed by colleagues in the field. Mintzer and other former students have also led the IEEE’s Signal Processing Society and contributed to the IEEE in myriad ways. Liu instilled in students a sense of responsibility and service to the community, said Mintzer.<br>Liu joined Princeton in 1962, an early occupant of the newly completed Engineering Quadrangle, and served on...