Issue link: https://digital.copcomm.com/i/83694
Stop-Motion Animation n n n n Mantra. For the characters, they used Pixar's RenderMan. tice, hopefully, but they are extremely impor- tant and allow animators to stay in a creative- performance mode." Big, Wide World But, the most dramatic role the visual effects crew played was in opening up the world for the filmmakers. "Ninety to 95 percent of the film has stop-motion puppets and miniature props and sets," Van't Hul says. "Things people made. But, occasionally, we remind the audience of the bigger world. Stop motion can feel claustropho- bic. Travis [Knight] gave us the task of expand- ing the world and opening the environment." Visual effects artists typically paint skies for stop-motion films. For ParaNorman, they cre- ated a volumetric storm. They also extended roads and streets in the town and populated it with digital extras. "We have a lot more CG elements in this film than in Coraline," Van't Hul says. "There was a conscious decision to open up the production value and make the world feel bigger." They did so in much the same way a vi- sual effects crew would enhance a live-action film. Despite the painstakingly slow, frame- by-frame performances, stop-motion is live action, and the visual effects crew needed to match the materials and scale of that stylized world. "We have to balance photorealism with what the directors want in style," Van't Hul says. "But the tools make it easier." As they might for a live-action film, the crew shot HDRI images of the sets to better match digital environments and characters with the practical sets and puppets. For HDRIs, they used exactly the same type of camera, a Canon 5D Mark II, that the animators and cinema- tographer used. During a chase sequence in which a blue van rockets through the town, for example, the crew extended the set with digital back- grounds and composited those backgrounds into the shot. Then, they tracked the practi- cal van in the shot, match-moved a CG ver- sion, lit and rendered the shot with the CG van. Lastly, they removed the reflections of the digital background from the CG van and ap- plied them to images of the practical van. The most dramatic environment the crew Digital Puppets In addition to the digital environments, an- other way in which the visual effects crew expanded the puppet's world was by mixing digital characters with real puppets in the school and in town. "We created digital ghosts, background adults for a mob sequence, and kids in the school," Van't Hul says. Eleven real puppets sat in the foreground of the school auditorium; the rest of the charac- ters in the background were CG. In the mob, puppets intermingled with CG characters. "The CG characters had to match the pup- created, though, was for the climax of the film in which an enormous face of a witch appears in turbulent storm clouds. "It would have been easy to have told the visual effects department that we needed a super natural storm," Butler says. "But our reference was an imperfect, handmade storm that [production designer] Nelson Lowry had come up with." To match the design, the artists created storm clouds out of tulle, material typi- cally used for ballerina costumes, animated the material clouds, and lit them. Then, the CG artists needed to match the practical element. In the sequence, volumetric CG clouds fill pets, even their skin texture," Van't Hul says. "We had multiple versions of skin. Background characters had rubber heads, which has a slight- ly different look and feel than the face-replace- ment heads. Our characters had to match each type. Our shader writers would hold a puppet and see how the light played off it." The effects artists also put a CG owl in a school play, moths in a teddy bear's mouth, and butterflies in the sky. "We really tried to use the computer to enhance the film," Van' the sky. "We used shapes and shaders and cloth simulations," Van't Hul says. The effects artists started building the sky using a series of curves in Houdini to construct the cloudscape, put hundreds of pieces of twisting cloth material based on the weave in tulle on top, and added the volumetrics. The cloth simulations gave the clouds a tactile feel, the volumetric effects added scale. A giant, greenish witch's face appears in the clouds, and as it moves through the sky, it impacts the volumes. Eventually, the witch resolves into a pup- pet that animators perform, but with CG enhancements. "They wanted her dress to be flowing and electric," Van't Hul says. "So we tracked and match-moved the puppet. We put a CG dress on her and gave her Tesla-coil-like hair. We didn't base the Tesla electricity on real electricity. We used a drawing that looked like someone had blown through a straw at ink spilled on paper. We wanted it to look like we had paid an animator to do an intricate, time- consuming thing for six months." The crew rendered the clouds in Side Effects' For the directors, the combination of CG and traditional effects is what gives the film its own identity. "We didn't want to make just another stop-frame film," Fell says. "There's no point going round the same track." Butler adds, "Years ago, CG was in danger of killing stop motion. Now the approach is to embrace the age-old technique and drag it into the next century through innovation. The scope, the set extensions, the digital back- ground characters, the face animation we can get with CG don't detract from stop motion. They add to it." By pushing the state of the art, the artists at Laika kept the tangible—real light, real textures, real photography. But with the help of computer graphics, they were able to take stop motion off the table and animate puppets with smoother, subtler performances. "I think we've got the best of both worlds," t Hul says. Fell says. n Barbara Robertson is an award-winning writer and a contributing editor for Computer Graphics World. She can a be reached at BarbaraRR@comcast.net. Use your smartphone to ac- cess a video interview with ParaNorman VFX supervisor Brian Van't Hul. August/September 2012 37