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See Inside July 2011

Light at the End of the Racetrack: How Pixar Explored the Physics of Light for Cars 2




Courtesy of Disney/Pixar

Although the stories told by Pixar Animation Studios take place in richly realized fantasy realms, the science and technology required to create those worlds have distinctly real-world origins.

For Cars 2, set for release in late June, the minds behind such films as Toy Story, Up and WALL-E had to study the complex ways in which light reflects off cars. The movie leaves behind the sleepy desert town setting of the original and takes place in the world of in­ternational racing, which meant having to depict many cars moving through varied tracks and racing surfaces. Producers quickly realized that Pixar’s existing 3-D lighting system would need significant upgrading.

“Cars are designed and painted to have a unique relationship to color and light,” says Pixar lighting team member Sudeep Rangaswamy. “So we needed to explore how light plays off of fast-moving vehicles—and how their movement and reflective qualities play off of the surrounding environment.”

A research team at Pixar studied the light-absorbing qualities of auto paint, carbon fiber and chrome, as well as the darkness-penetrating intensity and reach of standard and LCD headlights. The results were programmed into algorithms that calculate and render in real time the frequency and temperature of light and color on reflective,
absorbing and distorting materials.

That research was then integrated into a new lighting engine—software that allows animators to create scenes that appear to be illuminated from any angle, just the kind of effect a real-world director of photography would aim for. The lighting engine integrates with a virtual camera system, which allowed director John Lasseter to create scenes from any camera perspective. “The new engine allows lights from the scene to interact correctly with the characters the animators place within it,” Ranga­swamy says. “For example, we re-created downtown Tokyo for the film with all its neon lights. The engine created those lights with its [artificial intelligence] and maintained them—automatically, creating the correct lighting relationships.”

Thus, as Lightning McQueen races, the track lights and neon signs reflect off of his red paint, and that red glow can now reflect in a puddle as he passes, which alters the color of the car next to him—­all without the animators needing to render these effects “by hand” from scene to scene. The new lighting technology will remain in Pixar’s proprietary software toolbox for future films long after Cars 2 rolls over the horizon.

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