Ken Torrance’s accomplishments

Ken Torrance, 69, passed away unexpectedly February 15. His last name should be familiar to many of you: Torrance-Sparrow and Cook-Torrance are two reflection models that bear it.

He was a professor in the mechanical and aerospace engineering department at Cornell. Don Greenberg, head of the Program of Computer Graphics at Cornell, was his long-time collaborator and was one person who spoke today at a gathering in remembrance of Ken. He talked about how Dr. Torrance was not a man who blew his own horn, how he was humble about his contributions. The main thing for Ken was that he loved to teach. Some early accomplishments Don noted (with my own additions):

  • Published in 1967, Torrance-Sparrow was based on his PhD work (Sparrow was his advisor). It is a reflection model that was based on experimental data combined with theory. Microfacet theory had been around since the 1920’s, but had problems, such as going to infinity at an incidence angle of 90 degrees. Torrance-Sparrow describes off-specular peaks, i.e., the phenomenon where the brightest reflection off of roughened metal is not in the reflection direction. It’s worth noting that Blinn’s reflection model is directly derived from this work, putting it into vector form.
  • Cook-Torrance, in 1981, should be more familiar to computer graphics people, coalescing ideas about microfacet distribution and Fresnel reflectance and bringing in the idea of wavelength dependence. Rob Cook is currently the VP of Software Engineering at Pixar.
  • The idea of using heat transfer theory in computer graphics is Torrance’s idea, along with Greenberg; another great example of how cross-pollination between fields can yield fantastic results. The paper by Goral et al. (including Ken) in 1984 describes computing diffuse-diffuse interaction. It introduced two concepts to the field that have become key elements of global illumination theory and practice: form factors and radiosity. What’s interesting to me in this paper is that it includes something somewhat rare in our field, an explanation of an experimental setup to compare computer-generated results with reality. It’s the paper where the Cornell Cube was first used (empty! It made visibility computations ignorable). If you want to try a form of this experiment, look here.
  • I could go on and on, the themes being simulating light transport and materials along with physically measuring BRDFs and illumination spectral distributions—theory and experiment. You can see some other papers listed here. Here’s the measurements lab in 1995. SIGGRAPH recognized his accomplishments in 1994, giving him the Computer Graphics Achievement Award that year.

I had a passing acquaintance with Professor Torrance over the years. I was working on ray-traced shadows, not radiosity, during my time at the Cornell PCG lab from 1983-85. I recall seeing a photo on a monitor in the lab one night and asking Cindy Goral about it, why it was scanned in. She told me it was an image she had generated with radiosity techniques, which was utterly flabbergasting to me. Dr. Torrance was a smart guy and a nice person, but I didn’t know him much beyond that. All I knew was that he was helping Cindy, and in his life many other students, make astounding images.

If you have a personal memory of Ken, you may wish to leave a note in the family’s guestbook.

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