Computer Graphics World

November 2008 23 CG Animation n n n n 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. e 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 technol- ogy called Deep Canvas (See "Deep Back- ground," 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 tech- niques 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.' " e 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. "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 expres- sion-based XGen software grows virtual cards—2D planes—on the geometry in the scene. For each card, XGen associates partic- ular brushstrokes from the reference library. "at gives us a way to get the brush- strokes 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 go- ing to look." Brushing Light In addition to XGen, Disney's look de- velopment tool kit includes a 3D paint program and shader expressions, all rolled into a powerful system that allows artists to create procedural expressions without hav- ing to write procedural shaders (see "Fast Forward," April 2007, and "e 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." erefore, artists using the pro- gram 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." e new "normal mapping" technology allowed artists working on Bolt to give the surfaces of the painted geometry a brush- stroke quality by working with surface normals—the imaginary lines tangent to the surface of geometry that renderers use to calculate specular reflections. "We re- mapped the normals to brushstrokes so the surface appears to be made of many brush- strokes," 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. en, they painted individual grout lines between the bricks to create and save a more detailed layer. e painters created these two types 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."

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