"We also had to pay close attention to the clavicle and shoulders, especially with these cats because they have to be quadruped. Kitty always talks about the Call of the Wild and raises her arms. Her armpits caused problems and we asked a lot of the model and rigging guys to have her get down on all fours and raise her arms over her head."

Meanwhile, Imageworks concentrated on the two lead dogs, Diggs (James Marsden) and Butch (Nick Nolte), as well as the feline Catherine (Christine Applegate). Imageworks also shared assets for Catherine and the pigeon Seamus (Katt Williams). Overall, Imageworks created about 500 shots, evenly split between CG characters and face replacements of real animals.

"The twist was that we were building the full CG character and then extracting a facial pipeline for the face replacement of the same character," explains Rich Hoover, visual effects supervisor at Imageworks. "All the R&D happened to make the character match the real animal, and then we wrote some special tools to ensure really accurate tracking for facial capture on the real animal. This made our facial expressions really successful.

Like Tippett, Imageworks played to its existing animation strengths. "I found Catherine to be the most difficult because of how hard it is to capture the skin surface and skeletal placement accurately due to the fur," Hoover suggests. "We did our usual extensive acquisition of the character with multiple still cameras, almost a 360-degree view at the same instant. But it's difficult to accurately see where their skin is. We measured the hair dab in several places in the body and accomplished what we needed.

Imageworks also had two notable action sequences: Butch chases Seamus over San Francisco with Diggs on his back and a CG James Bond-like apparatus strapped to him, and the climax in an amusement park, which features a CG apparatus that unfolds and becomes Kitty's secret weapon and contains CG animals climbing all over it and chasing each other.

"We built a 2.5D, 360-degree environment of the theme park so that Brad could direct any kind of camera move he wanted as that action occurred," Hoover adds.

Hoover says "the biggest challenge in this kind of movie always is the requirements of the character: How much actual departure from a real character is there? And is that the kind of movie the filmmakers want to make? In this case, we folded back and forth between quadruped dogs and cats and anthropomorphizing them to do things that an animal wouldn't do. And then the normal requirement to make a CG character that can cut back and forth with a real animal."

Bill Desowitz is senior editor of AWN & VFXWorld.