Back to the future
Issue: Volume: 31 Issue: 11 (Nov. 2008)

Back to the future

It isn't easy being a superdog, as the little American white shepherd dog with the black lightning bolt on his side discovers in Bolt, Disney’s latest animated film. Bolt, the dog, stars in an action-packed TV show, and the CG feature opens with an amazing chase scene. Bolt leaps through the air, stops the bad guys in their tracks with his superbark, and, most important, rescues his co-star, Penny, from the green-eyed villain. Then, it’s over. The director yells, “Cut,” the crew takes Bolt back to his trailer, and Penny goes home.

The production crew, we learn, wants little Bolt to believe he really does have superpowers; they won’t let him live a dog’s life with Penny. And, he does believe. So, when a series of mishaps put him outside the trailer where he spots the green-eyed man, he believes the villain has kidnapped Penny again. He races to her rescue, only to land in the back of a truck heading for New York City. And that’s when Bolt’s real adventure begins.

Directed by Chris Williams and Byron Howard, Bolt stars the voice talents of John Travolta as Bolt and Miley Cyrus as Penny. It’s the first film shepherded through Disney Animation Studios by John Lasseter, who arrived as chief creative officer at Disney in 2006 following the Pixar acquisition.

“Every artist in this building is operating at a level they’ve never operated at before because of John Lasseter,” says Clark Spencer, Bolt producer. “Four years ago, this was a completely different film, with a different title and different directors. This movie would not be what it is without John Lasseter’s involvement in it.”

Four hundred artists worked on the feature for 88 weeks, producing approximately four seconds of the film per week. Lasseter chose the directors: Williams directed Disney’s first 3D short film “Glago’s Guest,” wrote the story for Mulan and The Emperor’s New Groove, and received an Annie nomination for the latter; Howard was a supervising animator on Lilo & Stitch and Brother Bear, an in-between artist on Pocahontas, an animator on Mulan, and received an Annie nomination for his character animation in Brother Bear. For Bolt, Howard tended to concentrate on the animation side, while Williams focused on the story.

“John [Lasseter] loved the essence of the story we had, that a dog lives on a TV show and only knows the TV show, and is thrown into the real world and discovers [his previous life] is a lie,” Clark says. “And then he returns to the little girl to find out if she was acting.”
Bolt, the dog star of the fi lm Bolt, owes the look of the painterly CG background behind him (at left) to new technology invented at Disney Animation Studios for this project.

In the film, once Bolt is in the real world, he tangles with a street cat named Mittens. Later, a hamster named Rhino, who lives inside a glass ball, rolls into the adventure. Here’s the dynamic among the three: Bolt believes Mittens will lead him to the green-eyed villain and, thus, to Penny, so he leashes the cat to his collar. Mittens quickly realizes who Bolt is and ridicules his supposed superpowers. Rhino, on the other hand, a nerdy fanboy who has memorized every “Bolt” TV show, totally believes in his hero and encourages Bolt to display his superskills. When Bolt warns Rhino that their journey could be dangerous, the little hamster replies from inside his glass bowl, “I eat danger for breakfast.”

“Rhino is like the kid who would throw a towel around his neck like Superman and jump off a roof,” says Nathan Greno, super­vising storyboard director, who joined the crew as Lasseter and Ed Catmull took the reins at Disney Animation. Although Bolt was always a dog and Mittens always a cat, originally Rhino was a rat. “Everything was up for grabs,” Greno says. Rhino turned into a hamster during a retreat.

“We were with about 35 or 40 directors from Pixar and Disney, and someone said, ‘I always wanted to do a hamster in a ball,’” Clark says. “We all knew, at that moment, we’d have a hamster in a ball.”

Animal Truth
Disney casts animators based on their skills, and organizes the supervisors by character. Sixty-two animators worked on Bolt, led by six supervisors. Clay Kaytis led the team of animators working on Rhino.

“Of all the characters, Rhino has the most controls,” Kaytis says. “He’s the most complicated because he is fat and round, and volumes want to crash.” The animators worked in Autodesk’s Maya using rigs that allow for squash and stretch. Deformers rode on the topology to simulate what a muscle system would do, but calculated the blendshapes only on surface changes. Kaytis moved Rhino’s belly with a control button; the hamster’s whiskers, though, moved automatically.

All the animals talk, except when humans are on screen, and the animators started working on shots by listening to the dialog. “I started with the character in a set, in a layout pose,” says Kaytis. “Then I listened to the audio over and over, to understand what the throat is doing and when to take a breath. I did five frames of poses to show the director. And then I shut the door and worked for a couple days.”
Rhino is the most anthropomorphic of all the animals because he stands up inside his bubble; otherwise, all the four-legged animals stay on all fours. “John [Lasseter] has certain rules,” Kaytis says. “Well, maybe not rules, but consistencies. His mantra is truth in materials; something has to move the way it looks. So, if an animal looks like a dog, it should move like a dog.”
Rhino, the hamster in the ball, tells his hero Bolt that he’d be a big help. Mittens, the cat leashed to Bolt, isn’t convinced. About 400 artists, including 62 animators, worked for 88 weeks on the film.

Although Bolt looks cartoony in his TV show, when he’s outside, he’s in the real world, which meant he needed to move realistically. To help the animators understand real-world animal behavior for the dog, cat, hamster, and other critters in the film, Disney had trainers bring various animals into the studio and had Dr. Stuart Sumida, a biology and anatomy professor at California State University in San Bernardino, teach classes. In addition, Rhino animators could observe a real hamster named Doink, which joined the crew and had his own glass ball.

Sometimes, though, the filmmakers needed to fudge accuracy. For example: “We reached a point when we thought we had nailed the dog,” Kaytis says. “We had animated a couple sequences. But he wasn’t appealing. So, we looked at the dogs in Lady and the Tramp, at the shape of their brows, how their muzzles worked, their ears, and their eyes-to-face relationship. And then we remodeled Bolt’s face.” They gave him a larger brow ridge, made his eyes bigger and rounder, and changed the fur color on parts of his face.

Dogged Artists
Art director Paul Felix—who came to Bolt with credits as a production designer for Lilo & Stitch and The Emperor’s New Groove, visual development artist for Brother Bear and Mulan, location designer for Tarzan, and character designer for Mulan—also considered Lady and the Tramp when he began working on the film.

The journey that Bolt, Mittens, and Rhino take from New York City to Hollywood sends them trotting (and rolling) across the US, which meant the crew needed to design and build what Adolph Lusinsky, the film’s look and lighting director, calls “200 environments on a 30-environment budget.”

To design the environments, Felix referenced early Disney films and the Ashcan School of art. “I liked the sense of place in Disney films like Mickey and the Beanstalk, Peter Pan, and Pinocchio, and the dirty quality and looseness in American painter Edward Hopper’s architectural settings,” Felix says. Hopper’s watercolors and paintings often include Impressionist background buildings and simplified geometry, which, while accurate in detail, is nonetheless abstract. “I like the idea of simple characters as a good foil against painterly backgrounds,” Felix says.

Achieving painterly backgrounds with computer graphics, however, isn’t always easy, and the job of translating Felix’s vision fell to Lusinsky. “We worked with R&D for a year to develop tools and processes to achieve the loose brush style in the early Disney films,” Spencer says. The result: new technology; so new that Disney has filed for patents on it.

Lusinsky groups the new technology into four areas: ray painting, normal mapping, texture painting, and painterly shadows.

Loose Edges
In 1999, Disney animators sent Tarzan, a 2D character, swinging through painterly 3D jungles with the help of new technology called Deep Canvas (See “Deep Background,” July 1999). Background artists painted on 2D plots of 3D scenes. Deep Canvas then applied information about each brushstroke to positions in 3D space. But, Deep Canvas relied on a proprietary renderer, and for Bolt, the crew wanted to use Pixar’s RenderMan.

“We came up with new ideas and techniques that involved raytracing, to put the brush strokes in 3D space so we can use the brushstrokes on silhouettes in CG models,” Lusinsky explains. “We call it ‘ray painting.’”

The process starts with painters working in Adobe Photoshop or Corel Painter to create and store libraries of brushstrokes. For Bolt, to create the Edward Hopper-like backgrounds, they used a dry brush.
Bolt, who believes he really is a superdog, thinks he’s helping Penny escape from the villains, but it’s only television fakery. The Bolt look and lighting team based color curves and contrast ranges for the movie on two film stocks, one for scenes in the TV show and another for the “real world.”

“We’re only interested in the quality of the edges,” Lusinsky points out. “We want the edges to feel like brushstrokes. If we had painted on the geometry, the sides would recede in space. In contrast, our brushstrokes never recede in space; they stay on the edges because they can track with the camera and stay flat to the image.”

To make this possible, the studio’s expression-based XGen software grows virtual cards—2D planes—on the geometry in the scene. For each card, XGen associates particular brushstrokes from the reference library.

“That gives us a way to get the brushstrokes onto a piece of geometry in 3D space,” Lusinsky says. “We never render the brushstrokes. We render the final model and then send a raytrace. When the ray hits a brushstroke, it sends information back to the geometry. It says, this is what brushstroke I am, and this is how I’m going to look.”

Brushing Light
In addition to XGen, Disney’s look development tool kit includes a 3D paint program and shader expressions, all rolled into a powerful system that allows artists to create procedural expressions without having to write procedural shaders (see “Fast Forward,” April 2007, and “The Sky’s the Limit,” November 2005).

“Our Paint3D program for painting textures is powerful,” Lusinsky says. “You don’t just paint in it; it has an expression library.” Therefore, artists using the program can easily and quickly move back and forth between procedural and hand-painted textures.

For example: “You can bring different properties of the geometry into Paint3D,” Lusinsky says. “If you pull the normals in as images and paint on those images, they’ll remap to the geometry, so the geometry thinks it has a new normal.”

The new “normal mapping” technology allowed artists working on Bolt to give the surfaces of the painted geometry a brushstroke quality by working with surface normals—the imaginary lines tangent to the surface of geometry that renderers use to calculate specular reflections. “We remapped the normals to brushstrokes so the surface appears to be made of many brushstrokes,” Lusinsky explains. “As the specular light falls across the surface, it gets broken up and takes on a brushstroke quality.”

Impressionist Painting
To further help the artists create painterly backgrounds in Edward Hopper’s style, the technical crew devised technology they call “Look A, Look B” for texture painting.  Lusinsky uses a brick wall to explain how the new tools worked in practice. First, the artists painted and saved an Impressionistic layer in which, for example, one brushstroke might represent 20 bricks at a time. Then, they painted individual grout lines between the bricks to create and save a more detailed layer. The painters created these two types of layers for each material in Bolt.

“When we rendered the materials, we could decide whether we wanted a looser, abstract interpretation, or more detailed look,” Lusinsky says. Sometimes, the artists made the decisions arbitrarily; other times, they set up the system to make procedural decisions based on depth cues for example, to render less detail when a material is some distance away from the camera, or, similarly, to render looser details in shadows.

Lastly, to create painterly shadows, the technical team developed new technology that works within RenderMan to fringe the shadow edges. “We developed tools and techniques that give the edges a different color than the interior,” Lusinsky notes. To do that, the shaders referenced libraries of painted brushstrokes.
Animators gave Bolt cartoony superpowers when the dog starred in his TV show. When Bolt travels through the real world, though, the animators followed John Lasseter’s maxim of “truth to materials,” and made sure the little dog behaved as a real dog would.

For the deep shadows in the characters’ hair, though, the crew leveraged the capabilities of technology already within XGen. “XGen keeps track of where each groom (guide) hair grows, how many hairs are associated with it, how far away it is from the camera, how big, and so forth,” Lusinsky says. “Because it is open-ended and anyone can write expressions or plug any kind of code into it, we used XGen to shade the hair in a more art-directable way. Rather than being dependent on volumetric shaders, we derived volumes of hair using information from XGen, which helped speed up hair renders quite a bit.”

Believable Light
For cinematography, Felix turned away from animated films and toward live-action movies of the early ’70s. In particular, he liked Vilmos Zsigmond’s cinematography in Heaven’s Gate and the “soft sensibility of light” in Ridley Scott’s McCabe & Mrs. Miller. Scott’s photography in the “traveling picture” Thelma & Louise also inspired him.

On the technical side, Lusinsky’s team studied film stocks, particularly older ones. “We developed film curves that all the renders used on our show,” he says. “That gave us a painterly textural world that seems photographic because the light is photographic.”

One film stock provided the color curves and contrast range for the sequences in which Bolt stars in the TV show; the other provided correct exposures for the rest of the movie, when Bolt rumbles through the real world. To accurately light Bolt’s journey across the country, Lusinsky and others traveled his route themselves.

“We wanted to have a naturalistic feel for the lighting, so we spent a lot of time studying light across the country,” Lusinsky says. “We wanted to capture the quality of the light in each area and pull color palettes from each area.”

To light shots in the garment district of New York City, for example, they developed a desaturated color palette that mimicked humid afternoons when the sun is soft and muted. In Ohio, they discovered that the humidity in the air tended to cast the sky a turquoise color. For Los Angeles, they rendered the sun hot and hard.

“We really tried to capture the subtleties that make each place different,” Lusinsky says. “The light, the architecture, the foliage. We wanted to be true to the locations so you felt like Bolt was in the real world. We thought if we made it too stylized, people wouldn’t believe he’s in a real world; it would feel like fantasy. We wanted it to be believable. And, John Lasseter is really big on details in the environments.”

When Lasseter and Catmull arrived at Disney Animation, they tore down walls, literally and figuratively. Formerly walled-off offices became an open conversation pit with a jukebox, magazines, and a cereal bar. Layers of management peeled away, too, which invigorated the studio with new, creative energy.
“Before John [Lasseter] and Ed [Catmull] arrived, I kept saying how great it would be if we had a boss like John,” Howard says. “He’s like a big kid who loves animation, and that enthusiasm filters through the crew.”

Williams adds, “John brought so much energy and excitement. He raised the quality bar. He gave us a real creative surge.”

Bolt was the first lightning rod for that renewed energy, and it could hardly be more fitting. In the film, the star learns that he doesn’t have superpowers. In making the film, the animation studio remembers it does.

Barbara Robertson is an award-winning writer and a contributing editor for Computer Graphics World. She can be reached at