Issue link: https://digital.copcomm.com/i/18322
n n n n CG Characters Tale of Two Kittys At times, Kitty Galore acts like a cat, while other times she exhibits human-like be- havior. Thus, for Cats & Dogs 2: The Revenge of Kitty Galore, the team at Tippett had to use what amounted to a two-rig system to animate the film’s vengeful cat. For the most part, the animators used a low-resolution rig—which did not have The Maya kitty model has a detailed muscle system. The realistic wrinkling of her skin required a number of new techniques. the artists had to duplicate the vector displace- ment and the mixing of the various maps, all within the studio’s new fur system. “Hairless cats have patches of long fur on their tail, head, and legs, as well as a full sheen of peach fuzz that is important to the look,” Farnsworth notes. “Te hairs must displace along with the surface or they would get swal- lowed by the wrinkles, or, conversely, float above in space. Synchronizing the displace- ments between the fur and the shading system took some vigilance.” As Liedtka notes, Tippett’s new fur system was especially important because the fur had to sync with the displacement shader for her wrinkles. “Te new fur system was node-based, so R&D just wrote a node to mirror what RenderMan was doing in order to create the displacement in the shader, and the fur would then track to the displaced skin,” he explains. Lastly, the artists used a two-pass subsurface scattering technique on Kitty’s skin, which also took advantage of the wrinkle data to colorize the stretched skin. Insofar as Kitty Galore’s skin goes, the team used a lot of reference and painted a lot of maps to match the character’s look. “We had some reference where she had dark spots on her nose that almost looked like dirt. It was tricky balancing that detail because it was hard to get it to look natural,” says Liedtka. For the skin, the artists procedurally added a bit of blushing when her body was compressed and lightened it more when she was stretched out. “On some shots, it was a bit too much, but on most shots, it was another small ingredient used to build up her complexity to make her feel a bit more real,” he adds. Te task of putting Kitty together fell on Aharon Borland, technical art director/look de- veloper, who branched off the studio’s standard shaders to create special shaders for the surface and displacement. “It was a long process to get a natural-looking result from the shaders,” notes Liedtka. For the lighting, the group used image- 36 October 2010 any of the muscle/skin plug-ins and could be moved around in Autodesk’s Maya in real time—to work on the shots. Once the shot reached a certain point, a rigger then added the animation to the muscle/skin rig, integrating the proper amount of jiggle, flexing, and sliding for the muscles and skin. Once this was complete, the result was cached out and sent to the TDs for rendering. “One of the big challenges was creating an anatomically correct cat that could per- form the movements of a human actor,” says Eric Jeffery, lead character rigger. “Cats and people have a very different range of motion. Keeping our Kitty rig looking like a cat while giving it the expanded movements of a human was difficult. In a way, it was almost like making two rigs. We would get the puppet looking great in shots of Kitty performing like a real cat, and all of a sudden she’d switch to a more human style of acting, and we’d have to go back and tweak things so she didn’t break.” According to Jeffery, the team added a number of cheats to make the model work in both worlds. For example, there are significant differences between the arm of a cat and a human, and in the film, Kitty spends a lot of time gesturing with her arms. This meant wrist twisting that is not possible for a real cat to per- form. “By getting nice skin sliding and muscle flexing on Kitty’s arms, however, it appears to be a more natural type of movement,” notes Jeffery. Another significant challenge was getting Kitty’s face to wrinkle up properly as she delivered her performance. To achieve the best result possible, the crew set up controls on the surface of the model that looked at how much skin was moving in a certain direction, and when it reached a certain point, a specific wrinkle map was fired. This method gave the animators a more natural look, as opposed to linking wrinkle maps to a specific blendshape. Several of the cat’s blendshapes would move the skin on parts of the face in a similar fashion. Because of this, link- ing to specific blendshapes would have created a lot of redundancies. “Instead, our rig looked at how the skin was moving around on several pre- defined areas of the cat’s face,” Jeffery explains. “For example, if the skin on the brow moved back toward the top of the skull, regardless of what facial expression was causing it, our system was smart enough to fire the proper wrinkle map.” In the film, the CG Kitty Galore interacts with her CG pet mouse. In fact, in most of the Kitty shots, the digital feline was far more talk than action. As a result, many of her shots were close-ups, requiring the animators to come up with some signature tricks and moves for her. Just like in the Bond films, she has a white, fluffy pet that she strokes, but she takes it too far. “For us, that meant a lot of interaction between two CG characters because she carries, pets, throws, jabs, and hugs her little pet Scrumptious,” notes co-visual effects supervisor Scott Liedtka. I guess you could say that this behavior led to a cat-and-mouse game of sorts for the crew at Tippet. –Karen Moltenbrey based lighting from HDR images captured on set. Nevertheless, Kitty was still tricky to fit into the plate because she had so much scatter. “Her fuzz had to inherit the lighting of the skin, and its scatter, too. She worked best when a simple lighting setup could be used,” says Liedt- ka. “Once things started to get too fussy, though, it was hard to make her feel all put together; she started to feel like a lot of little pieces.” Just like the Sphynx breed which she was modeled after, the hairless Kitty Galore was certainly atypical. She challenged the artists at Tippett—who are by no means inexperienced when it comes to creating realistic digital ani- mals—with her unique look and style. “All in all, the individual ideas we used [to create her] were not revolutionary. But the combination of techniques on such a large scale made for a complicated character, and finding the right technique took some time,” notes Farnsworth. n Karen Moltenbrey is the chief editor for Computer Graphics World.