A new painting tool in Adobe Photoshop, a medical program, and the upcoming Disney movie, ‘Tangled’, are three results of the research of Columbia professor Eitan Grinspun and his graduate students.
Grinspun, an associate professor of computer science and director of the Columbia Computer Graphics Group (C2G2 ), and some of his graduate students have spent the last four years studying computer programming techniques that are seeing life far beyond the labs of Schapiro Hall.
Grinspun’s involvement in animation began when a friend and research scientist at Disney called the computer science department to consult with him on a problem that was frustrating the studio’s animators. In ‘Tangled’, which opens Thanksgiving weekend, the heroine’s multi-layered dress proved a “nightmare” to configure on the computer.
“Computers on their own don’t know anything about the fact that layers of clothing shouldn’t go through each other,” Grinspun said.
Animators either have to go through the time-consuming process of programming every combination of layers not to collide, or settle for allowing all the layers of the dress to move rigidly, as one entity.
At the time, Grinspun, Etienne Vouga (a Columbia Ph.D. candidate), and David Harmon, Ph.D. ’10, had already been working on animating collisions.
Although their initial aim was to solve more ambitious problems, “[they] noticed that a part of what [they] had done … could be used to improve how existing methods handle situations where tightly-bunched cloth is rubbing against itself and other objects,” Vouga said in an email from Berlin.
This solution, which the team called “inelastic projections,” simulates objects interacting with one another as they would in real life, no matter what forces, such as gravity or other objects, may act upon them.
Another technology the team developed, called RODS, has led to a better system of modeling graphic textures for hair that Weta Digital, the visual effects company behind Avatar and The Lord of the Rings, uses. That same technology was used to create a paintbrush tool in Photoshop CS5, the latest version of Adobe’s software. When painting in the revamped Photoshop, you can now watch the bristles move as though actually painting with a brush.
The team’s work is considered so cutting-edge in the field that “the studios know us and they invite us to visit and get in touch with us with problems,” Grinspun said.
“We would talk to them [Disney, Weta, Adobe] about our projects,” Harmon said. “We’d get an industry take on the things we were working on. Some people do research with blinders on and don’t really look at the big picture all the time and how relevant the stuff you’re doing is to people.”
Grinspun, Vouga, and Miklos Bergou, Ph.D. ’10, along with Basile Audoly, of UPMC University Paris 06, and Max Wardetzky, of the Universität Göttingen in Germany, had “decided to study the problem of simulating elastic rods … by looking at the geometry behind the physical system,” Bergou said in an email from San Jose, California, where he now works for Adobe. The project would simulate the behavior of hairs and “thin threads of fluid faster than [do] existing methods,” Vouga said.
“It had more of an academic interest for us in the beginning,” Bergou said, but when Weta approached the team, they realized the practical value of their research as a simulation for hair.
And when Adobe told Grinspun they wanted to develop a new tool to model a paintbrush, “we already had this simulation for a single bristle in effect,” Grinspun said. “The bristles on a paintbrush are nothing more than hairs.”
To the researchers’ surprise, the RODS project proved itself useful to another industry: medicine.
Doctors from Johns Hopkins “are using it to figure out how long needles move through the body,” Grinspun said.
The tips of needles are beveled, so as they go into flesh, they become directed. By twisting the needle, you can “steer through the body,” he explained.
Grinspun said that doctors, after a study by engineers at UC Berkeley, “are using a computer to predict how these needles will move through the body and avoid obstacles. This needle is nothing more than a stiff hair.”
Grinspun values a blend between science and artistry, a value evident in the flagship course he teaches at Columbia, Physically Based Computer Animation. His assignments require students to submit a computer program as well as a creative piece incorporating their program.
This philosophy was what ignited his interest in pursuing the career he has built for himself.
“I always liked geometry—shapes and stuff,” he said.
It was in college that he realized “how much geometry is related to physics. And I got excited by that, because I liked art and animation. And I saw this space for this nice connection between all these things.”
“The physics and the math are not going to make a good movie. You need an amazing story to make a good movie,” Grinspun said. “But the physics and the math can make the movie tell that story better. It can reinforce what’s happening in the story.”
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