Over the past 20 years, Pixar Animation Studios has pushed the limits of computer-animation to exciting new heights and continued to harness the medium to showcase their stories and characters in exciting new ways. From their earliest Oscar®-winning and nominated short films to the industry’s first full-length CG feature, “Toy Story,” Pixar has never been content to rest on their laurels. Each film has challenged them in new ways whether it was the blades of grass and crowd scenes in “A Bug’s Life,” the caricatured-but-realistic humans in “Toy Story 2,” the hairy characters and simulated clothing of “Monsters, Inc.,” the vibrant underwater world of “Finding Nemo,” or the action-packed environments and human characters in “The Incredibles.” Their latest undertaking, CARS, posed some of the greatest challenges to date.
Under the supervision of associate producer Tom Porter, supervising technical director Eben Ostby, and Pixar’s resident group of technical wizards, CARS got off to a fast start and scored some impressive achievements along the way.
Perhaps the biggest challenge for the CARS technical team was creating the metallic and painted surfaces of the car characters, and the reflections that those surfaces generate. An algorithmic rendering technique known as “ray tracing” was used for the first time at Pixar to give the filmmakers the look and effect that they wanted.
Ostby explains, “Given that the stars of our film are made of metal, John had a real desire to see realistic reflections and more beautiful lighting than we’ve seen in any of our previous films. In the past, we’ve mostly used environment maps and other matte-based technology to cheat reflections, but for CARS we added a ray-tracing capability to our existing Renderman program to raise the bar for Pixar.”
Ray tracing has been around for many years, but it was up to Pixar’s rendering team to introduce it into nearly every shot in CARS. Rendering lead Jessica McMackin was responsible for rendering the film’s final images, while rendering optimization lead Tony Apodaca had to figure out how to minimize the rendering time.
McMackin notes, “In addition to creating accurate reflections, we used ray tracing to achieve other effects. We were able to use this approach to create accurate shadows, like when there are multiple light sources and you want to get a feathering of shadows at the edges. Or occlusion, which is the absence of ambient light between two surfaces, like a crease in a shirt. A fourth use is irradiance. An example of this would be if you had a piece of red paper and held it up to a white wall, the light would be colored by the paper and cast a red glow on the wall.”
“Our computers are now a thousand times faster than they were on ‘Toy Story,’” adds Apodaca, “but even though they’re faster, our appetites have gotten bigger and we challenge ourselves more. Because of ray tracing and all the reflections, the average time to render a single frame of film on CARS was seventeen hours. Some frames took as much as a week. On this film, we’ve made larger and more beautiful images with more subtle lighting and ray tracing.”
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