'Crazy complexity' lies under vfx characters' 'skin'

Every breath “Up’s” Carl and Ellie take, every move “Avatar’s” Jake and Neytiri make, depends upon the animators, riggers and modelers who bend bits and bytes into believable emotional performances.

From the names of their jobs, it’s easy to picture what modelers and animators do. But riggers?

“The thing that nobody’s talking about right now is the rigging of the characters,” says “Avatar” helmer James Cameron.

CG characters look fully fleshed out, but each one is little more than a thin sheet of tiny polygons stitched into a skin that forms their shape. Riggers devise the mechanism — the rig — that animators use to move the skin and create the illusion that a character lives and breathes.

To move the body, riggers place a virtual skeleton inside the skin and attach control points to the joints like strings on a puppet. The joints move the bones, the bones move mathematical muscles, and the muscles move the skin. To create facial expressions, control points reshape the skin into smiles and frowns, ooohs and aahs. Riggers specify how these control points work — how a joint pivots, how far an eyebrow can lift.

“This is all transparent to the animators,” says Pixar’s Michael Comet, character modeling and articulation artist on “Up.” “(Animators) set a numeric value or move a control up and down, but behind the scenes is all this crazy complexity.”

Granny in the Oscar-nominated short “Granny O’Grimm’s Sleeping Beauty” looks fat because riggers caused her torso to squash and bulge when she moves, “Granny had a bit too much cake,” says character rigger Eoghan Garvey of Brown Bag Films. “She was tough to rig.”

The “District 9″ aliens’ unbending, insect-like faces posed an opposite problem. “I based the rig on natural human muscle patterns, but when an animator pulled a control, it shifted rigid plates around,” says Image Engine rigger Angela Magrath. For the bodies, motion-capture data moved the control points, with animators adding little twitches.

For the humanoid Na’vi in “Avatar,” Weta Digital gave animators a leg up by inventing a system that, once trained, automatically matched data from tracking points worn by actors to control points on the CG rig.

“Once we solved the first 10 closeups of Neytiri, the next 200 were right there,” Cameron says.

Then, to ripple muscles in the nearly naked Na’vi bodies, Weta developed a new secondary-motion rigging system. “We had to take our old system to the next level for this film,” says Weta creature supervisor Dana Peters. “Our new muscle system uses a full finite-element simulation.”

Not so for the Oscar nommed short “French Roast.” “We didn’t need to rig our characters to do everything,” says director Fabrice Joubert. “Only the actions in the story. It was very good for the budget.”

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