|Animal experts will tell you that, despite the age-old adage that cats and dogs do not get along, a positive relationship between the two is indeed possible, depending on the animals’ personalities. That said, it’s clear why the sourpuss Kitty Galore is at war with, well, just about everyone—dogs, humans, and even fellow felines—in the live-action feature film Cats & Dogs 2: The Revenge of Kitty Galore. What’s this rogue agent’s beef? She lost her beautiful coat at the paws of a dog, and soon after became ridiculed by her cat comrades and kicked out of her human home.
Kitty Galore’s baldness is at the root of her vindictive behavior. It also became a challenge of sorts for the artists at Tippett Studio who created Kitty Galore as well as approximately 10 other CG animals for the film. These computer-generated characters act alongside humans and animal actors, some of which have digital face replacements. “We had all the Kitty Galore shots, and she was a main character for us in about 100 shots,” says Scott Liedtka, Tippett’s co-VFX supervisor on the film.
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The Tippett group used the studio’s brand-new hair system, Furator, to create the computer-generated animals’ coats (see “Here Kitty, Kitty in the Web Exclusives section on www.cgw.com). That even holds true for the “hairless” Kitty Galore, who does not have a thick pelt but is covered in a fine layer of peach fuzz. “We had a few big challenges [on the film], but the one that you see on the screen is Kitty Galore herself,” says Liedtka. “Trying to match a hairless Sphynx cat with all those creepy wrinkles and no fur to hide her skin and muscles was a big job. We tried many techniques and ended up mixing a few to get her to work.”
The tale of Kitty Galore’s accident is recalled in a flashback with just a couple of shots, so luckily Tippett didn’t have to create a fully furred Kitty, too. Nevertheless, she still has some longish hair strands on her face, ears, feet, and tail that was a bit thick in some areas, while over the rest of her body, she has a short coat of peach fuzz that made her skin look velvety. The group initially tested a faux fur shader on her, but Liedtka did not believe it would have held up well in the close-ups. In the end, Kitty ended up with a couple million hairs.
Hairy Situation Crafting realistic animal fur is quite challenging, but creating this so-called hairless cat was even more difficult. “The wrinkles, muscles, and skin shading all had to be pretty sophisticated to be convincing,” says Liedtka. “As hard as fur is, it also can simplify things. As long as the fur looks good, the character looks good.”
Creating furry CG animals can be tricky, but creating one that is hairlessproved to be even more challenging, as the artists at Tippett discoveredwhile creating the evil character Kitty Galore for Cats & Dogs 2.
To make Kitty Galore look good required the team to improve on a number of techniques that Tippett had been developing over a number of shows: tangent space vector displacement, pose space data to drive the displacement shader, pose space corrective blendshapes, shallow and deep subsurface scattering using blocking objects for skin shading, Tippett’s own so-called “eyemagic” technique to help compositors fine-tune the eyes with more shadow and depth. “The individual ideas that were developed for Kitty Galore were not especially difficult, but the combination of all the techniques ended up being a hard task to accomplish,” he says.
To create Kitty Galore, the Tippett crew watched countless videos of Sphynx cats, a rare breed known for its lack of a coat. Compositor Shelley Campbell, who owns such a pet, brought it into the studio so the team could see up close how much muscle shape and movement was visible at the skin’s surface, and how the skin wrinkled. “Having reference like this was priceless,” says Eric Jeffery, lead character rigger.
The CG Kitty Galore was built in Autodesk’s Maya. For the musculature, the puppet department created a detailed muscle system using Maya Muscle for simulating muscle bunching and jiggling. The artists also used the muscle system to simulate bones—such as the scapula—moving under the skin.
According to Jeffery, due to the countless variables at play in a cat’s anatomy, a Sphynx cat’s wrinkles rarely appear the same way. “Because we were able to spend time watching our reference cat, we were able to isolate the most commonly occurring wrinkle patterns and re-create them onto our digital Kitty puppet,” he says.
Tale of Two Kittys At times, Kitty Galore acts like a cat, while other times she exhibits human-like behavior. 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 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 perform 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 perform. “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, linking to specific blendshapes would have created a lot of redundancies.
“Instead, our rig looked at how the skin was moving around on several predefined 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.
To achieve the realistic wrinkling, the group had to develop a technique that used tangent space vector displacement driven by a combination of strain from the mesh and a pose space system for problem areas that needed specific sculpts. In addition, Kitty required fur system development, skin-shading improvements, and a beefy muscle system—in addition to the studio’s facial animation system and animation rig to support her over-the-top acting. “All the departments were pushed pretty hard to get her to work,” Liedtka says.
Specifically what made Kitty Galore so difficult to create, according to Mike Farnsworth, graphics software engineer, was the fact that she had so many wrinkles and that her muscular definition changed as she moved, making it too difficult to track those variations manually. Alternatively for her skin wrinkles, the modelers created a form of vector displacement for use in Pixar’s RenderMan that followed her animation and enabled them to mix as many as 75 displacement maps based on her movement and dialog. The data for mixing the wrinkle and muscle sculpts was generated with custom Maya plug-ins that analyzed her skin stretching and facial poses. The sculpts themselves, which were the basis of the maps, were created in Pixologic’s ZBrush and Autodesk’s Mudbox as high-resolution meshes distilled down to fairly large EXR images with a custom tool that operated on the GPU.
“Our incarnation of vector displacement is encoded in tangent space, with some special handling for texture seams. It works fairly well on subdivision surfaces, our primary mesh type,” says Farnsworth. “The pose plug-in within Maya handled natural transitioning between sculpt mixes. We don’t know of anybody using that same flavor of solver that we used on Kitty.”
The final displacement shader was somewhat complicated, says Farnsworth, as it took into account all the mixing data and all the displacement maps. “It had to be optimized to minimize the number of displacement maps used, or else the texture-caching system would have slowed to a crawl,” he adds.
It was important that the shader synchronize with Tippett’s fur system so that the fur on Kitty’s body tracked with the wrinkles. Thus, the artists had to duplicate the vector displacement and the mixing of the various maps, all within the studio’s new fur system.
The CG Kitty Galoreinteracts with the CGmouse, Scrumptious.
“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. “The hairs must displace along with the surface or they would get swallowed by the wrinkles, or, conversely, float above in space. Synchronizing the displacements 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. “The new fur system was node-based, so the developers in 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 now 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.
The Maya kitty model has a detailed musclesystem. The realistic wrinkling of her skinrequired a number of new techniques.
The task of putting Kitty together fell on Aharon Borland, technical art director/look developer, who branched off the studio’s standard shaders to create special Kitty 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-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 peach 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 Liedtka. “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 to 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 animals—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.