The Jacobs School of Engineering assistant professor and two former colleagues -- Stanford University professor Pat Hanrahan and Cornell University assistant professor Stephen Marschner -- will be recognized for "their pioneering research in simulating subsurface scattering of light in translucent materials." The Academy, which rarely honors academics outside the movie industry, cited the professors' joint 2001 paper that laid out a "Practical Model for Subsurface Light Transport." That paper, on which Jensen was the principal author, provided a model for rendering the effect of light on translucent surfaces, such as skin or marble.
Even before the paper was published in 2001, Jensen was invited to speak at major visual-effects companies such as Industrial Light & Magic (ILM) and Pixar, which subsequently incorporated the technology into their visual-effects software. "It has been heartening to see how quickly Hollywood adopted this technology," said Jensen. "Almost all big-budget films with extensive visual effects now incorporate at least some elements of our model, and the industry is on its way to being able to create computer-animated human characters that truly look real."
Jensen has grappled with ways to replicate the appearance of natural phenomena and materials since the mid 1990s, when he developed a method called 'photon mapping' to replicate the look of light on a scene from one or more sources. That process is widely used in the computer-graphics industry, but the researcher recognized that it fell short when rendering translucent materials such as milk, marble, and snow -- or skin, eyes and teeth.
Previous visual-effects technology assumed that light on any surface reflects from the same point where it hits, as it does on a metal surface. The result: images that appear hard -- like rock or plastic. "That is why the early successes in digital animation, such as Jurassic Park and Toy Story, featured primarily non-human characters," explained the Danish academic, who is co-director of a new Graphics and Vision group within UCSD's Computer Science and Engineering department.
Drawing insight from a medical text, Jensen realized that existing effects did not take into account a phenomenon known as 'subsurface scattering.' On translucent materials, light penetrates the surface and scatters, and the photons then reflect out from various points away from where they entered, at varying angles. "This scattering effect below the surface was understood as a medical phenomenon, but wasn't incorporated into computer graphics until our model, which mathematically accounts for the way those photons scatter," said Jensen.
According to the Academy citation, "This mathematical model contributed substantially to the development and implementation of practical techniques for simulating subsurface scattering of light in translucent materials for computer-generated images in motion pictures."
Indeed, the Academy is bestowing a separate Technical Achievement Award to the visual-effects artists responsible for first implementing Jensen's model in the movie industry. ILM's Christophe Hery (Harry Potter and the Chamber of Secrets and Terminator 3), as well as Ken McGaugh and Joe Letteri (who supervised visual-effects on the second and third installments of the Lord of the Rings trilogy) were cited for developing those techniques to "create realistic-looking skin on digitally created characters," noted the Academy. "The character of Gollum in the Lord of the Rings trilogy and Dobby in Harry Potter will remain landmarks, because for the first time they gave movie-goers the sense that they were watching flesh-and-bone characters," said Jensen. "We are entering an era when skin can be rendered true to life, allowing audiences to forget that the character is synthetic rather than real. This is a disruptive technology that is changing the way people talk about perception of simulation."
Jensen also believes it is only a matter of time before the verisimilitude of characters such as Gollum and Dobby makes its way into videogames. "The accurate rendering of light under a translucent surface using our model requires much more computing power than is currently available," said Jensen. "But that will change as new game consoles such as PlayStation 3 reach the market and allow game designers to create characters and objects that absorb and reflect light just as they do in reality." (Sony's PlayStation 3 and other next-generation consoles are expected to be released starting in 2006.)
Related Links:
Jensen's Home Page http://graphics.ucsd.edu/~henrik/
'A Practical Model for Subsurface Light Transport' SIGGRAPH 2001 Proceedings http://graphics.ucsd.edu/~henrik/papers/bssrdf/