Computer Graphics World

August 2009 20 n n n n CG Characters•Stereo things. at gives it more impact, humor, and fun. Even though the film's target is kids, we wanted it to have a sophisticated action-film look and feel. We wanted to use as much realism as we could to make kids feel like they could have their own Transformers or Terminator." But, guinea pigs are never real in the film. Imageworks painted out any of the furry critters used on set, and replaced them with CG counterparts that could stretch beyond the real animals' physical limitations. "We wanted the guinea pigs to feel real, visceral, and tangible, but to tell our story, we needed to have them do some things the real animals couldn't do," Stockdyk says. Covert Critters Modelers and animators worked in Auto- desk's Maya to create guinea pigs that differed from the real animals slightly in their looks and sometimes more wildly in their actions. "We angled their eyes a little forward because otherwise we could look at only one eye at a time, and we changed their fur patterns subtly," explains Saliba, who led a crew that ex- panded to include 68 animators at the peak of the film's production. e fur stylists used Imageworks' in- house hair system. "One of the biggest issues was in getting the hair and fur to interact with all the gadgets," says Seth Maury, digital effects supervisor. "For that, JJ Blumenkranz, the CG supervisor, and hair lead Dustin Wicke came up with a magnet system." Rendering happened primarily through Pixar's RenderMan for the characters, and primarily through the studio's Arnold software for the backgrounds. Composi- tors, meanwhile, used Imageworks' own Katana system. "ere was a tendency by the executives and producers to want the guinea pigs more human, with big muscles and big arms and small heads, but Hoyt [Yeatman] dug his heels in," Saliba says. "He was adamant that they play like photoreal guinea pigs. But, in a single shot, they could go from acting like people to skittering across the floor like little rodents, and when they're around real animals in the pet shop, they have to act like real guinea pigs. So, we had to walk a fine line." at meant the team needed to create photoreal guinea pigs they could stylize without drawing attention to the carica- ture, and that could change from quad- ruped to biped within a single shot. Al- though modelers based the characters on real guinea pigs, because their physique couldn't cope with the extreme poses called for by the G-Force, modelers changed the bone structure of their legs and hands. For example, their hands could handle equip- ment and stunts, yet still perform in a guinea pig way. "eir hands needed the same function- ality as their feet because they run on all fours," Saliba says, "and their feet rig needed to allow them to roll from heel to toe eas- ily. Also, they have amorphous bodies that change quite a bit depending on whether they're climbing, stretching, bunched in a ball, sitting, or lying down." Shaper tools that worked within the Maya rig helped with the shape-shifting bodies. And rigs populated with precise controls allowed the animators to quickly switch from, for example, a forward- kinematics mode for their hands when the guinea pigs stood up, to an inverse-kine- matics mode when their hands become feet on the ground. e animals can talk via a translator gizmo invented by the scientist who orga- nized the G-Force team, which converts their squeaks into human speech—an idea also used by Pixar for the dogs in Up (see "e Shape of Animation," July 2009). at gave the animators freedom to con- centrate on the CG stars' physical perfor- mance without always having to lip-sync dialog, something the Pixar animators also used to their advantage. Guinea Pig's Eye View To help envision the shots, the Image- works' animators would often videotape themselves acting to the dialog or perform- ing stunts. "ey import the video into a Maya scene and use that as reference," Saliba says. For additional guinea pig refer- ence, they found 20,000 videos of the pop- ular pets posted to YouTube, and observed some office pets. A search on YouTube to find reference footage for Speckles, the star-nosed mole, The pint-sized G-Force team must stop an 80-foot CG robot made from an assortment of con- stantly-moving mechanical parts.

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