Paul Van Campen Hough

Paul Van Campen Hough, originator of the key idea now known as the Hough transform, died on 11 January 2021 in Port Jefferson, New York, at age 95. The Hough transform is a method of line-element recognition that is one of the most widely used procedures in computer vision. He was a professor of physics at the University of Michigan, 1950–61, and senior physicist and senior biophysicist at Brookhaven National Laboratory, 1961–97.

Hough was born on 21 May 1925 in Ellwood City, Pennsylvania. He graduated from Swarthmore College after three and a half years in February 1945, as World War II raged. Paul went immediately to Los Alamos to join his physics professor, John Elmore, as an assistant on the Manhattan Project. Elmore developed the electronics used to measure the strength (multiplication constant) of the first atomic bomb in the Trinity test at Alamogordo, New Mexico. A photo from the Los Alamos National Laboratory archives shows Paul at the Trinity site with screwdriver in hand. Hough was a junior scientist but carried the special white badge—he kept it safe all these years—that admitted him to research discussions by Project luminaries Enrico Fermi, Hans Bethe, Richard Feynman, Robert Wilson, and many others. Memories of his six months at Los Alamos remained breathtakingly vivid.

Hough earned his PhD in 1949 at Cornell University, where many top physicists had returned or relocated at the conclusion of the Manhattan Project. His thesis advisor was Wilson. Hough joined the faculty at Michigan in 1950 as an experimental particle physicist, cyclotron manager, and popular course lecturer on nuclear structure, quantum mechanics, and classical electricity and magnetism. Donald Glaser, another professor at Michigan, had invented the bubble chamber in 1952, a tremendous advance for subatomic particle detection. New particles were captured as complex ionized tracks on photographic film that required painstaking analysis by human scanners. But existing data analysis was unable to keep up with the torrent of bubble chamber films being produced in the early 1960s. Hough responded to these needs with the Hough transform and the Hough–Powell device.

In 1962 Hough obtained a US patent titled “Method and Means for Recognizing Complex Patterns.” Its object was “to provide a method and means for the recognition of complex patterns in a picture.” Hough stated in his patent that bubble chamber charged particle tracks on film were among the complex patterns that could be analyzed with his method. Complex patterns were divided into sufficiently small straight-line segments. Each segment was transformed into slope and intercept data. In the plane transform, if points on the segments lie on a straight line, the corresponding lines in the plane transform will intersect in a point or knot. Not doubting his insight, Hough perceived this as an exact theorem. In the past 60 years, the Hough transform, as his method came to be known, has been widely adopted and, with added development by many users, has found increasing applications in image processing, graphics, computer vision, and in artificial intelligence for face recognition, autonomous vehicle navigation systems, and more.

In 1960 Hough took a sabbatical leave to CERN as a Guggenheim Fellow. Along with Brian W. Powell, a young CERN physicist, he envisioned a technique for the automatic exploration of photographs using computers. They produced what became known as the Hough-Powell device, an automated machine to measure bubble chamber tracks with novel use of a mechanical flying spot that “mechanized” film scanning. Development work continued into 1961 at Rutherford, Berkeley, CERN, IBM, and Brookhaven, where Hough had accepted a position as a physicist. Ten large-scale Hough-Powell devices were built in Europe and the US, as well as 16 smaller installations worldwide. Between 1964 and 1970, he continued research in particle physics using the device, discovering the g-minus meson and pi-meson/proton excited states in the 1–2 Gev resonance region. In 1963 the American Physical Society named Hough a fellow, an honor of which he was very proud.

In 1973 Hough took sabbatical leave from Brookhaven, again as a Guggenheim Fellow, at Cold Spring Harbor Laboratory, known for cutting-edge molecular biology. Its director, James Watson, had co-discovered the double-stranded helical structure of DNA, opening a new golden age of molecular biology. Hough was mesmerized, changed course, and headed into molecular biology. Recognizing his physics contributions, the Brookhaven director granted Hough tenure as senior biophysicist in the biology department in 1975. Hough developed a data analysis system for Brookhaven’s scanning transmission electron microscope, which made possible the discovery with collaborators of a double hexamer protein central to DNA replication in a mammalian virus (published in Nature, 1989). Thirty years later, John F. X. Diffley’s group also identified a double hexamer structure central to higher-organism DNA replication initiation (Nature, 2019) using the higher-resolution cryoelectron microscope.

Hough retired from Brookhaven in 1997. He continued development of a new atomic force microscope for the life sciences at the Stony Brook University High Technology Incubator and at the university’s Center for Structural Biology with Steven O. Smith. Hough received patents in 2004 and 2006 for a “single-touch” version of the microscope, called the sensing mode atomic force microscope, an improvement from existing continuous touch versions.

Paul Hough enjoyed the worlds of both particle physics and biological structure immensely. When asked though, he did admit with a smile, “You can take the boy out of physics, but not physics out of the boy.”