Computer Graphics World

August 2009 16 ■ ■ ■ ■ Visual Effects the Quidditch competitors performing a library of expressions. Before the crew started the capture, though, they had each actor do a minute and a half warm-up. "We had done the test with Rupert Grint, who plays Ron Weasley," Aithadi explains. "And, we asked him to do an ex- treme movement. When we got the data back, we could see blood moving inside his face in a specifi c way. I had never thought of that before. So the warm-up helped get the blood fl owing in the actors' faces." After shooting each actor, the artists at MPC used camera projection to apply the moving images on a CG model of the ac- tor's head, and then stitched the edges and The fastest way for a wizard to transport is by apparating: He or she thinks of a destination and magically teleports there. But, it's dangerous, so wizards cannot receive a license to legally apparate until they turn 17, Harry's age now. The question for the fi lmmakers was, what does ap- parating look like? To answer that question, artists at The Moving Picture Company (MPC) created drawings to visualize VFX supervi- sor Tim Burke's idea of something like chewing gum that causes Harry and Dumbledore's bodies to pull and deform, and blend into each other. "That was our biggest mistake," says Nicolas Aithadi, MPC's visual effects supervisor. "Tim loved our ideas. And [director] David Yates loved them. But we didn't have a clue about how to do them. I'd explain the ideas to our modelers and animators, and they'd look at me with empty eyes. The shot is eight seconds long, and it's the most complex we had to do, completely abstract from start to fi nish." In the fi nal shot, Dumbledore and Harry are standing in a train station. Dumbledore says, "Take my hand, Harry," and they apparate. The world spins around them and sucks them inside. They collide, their bodies distort and twist, and their clothing and skin blend together until you can't tell one from the other. For Dumbledore, it's magic as usual. For the nov- ice Harry, it's painful. Then, they pop out into a village. The team spent the fi rst two or three months tossing ideas like hot potatoes back and forth between the animation and modeling departments. Finally, they decided to start with models based on fi ve images that represented the stages Harry and Dumbledore go through as they transport. Meanwhile, the matchmove department rotoscoped Harry and Dumbledore—that is, actors Daniel Radcliffe and Mi- chael Gambon—from footage shot at the train station and in the village. And, the character development team designed a rig that allowed animators to stretch low-res models of the characters in abnormal ways. In addition, one modeler cre- ated a train station in CG and then, without changing the topology, turned the train station into a village. Hand modeling also helped transform the characters. "We didn't have time to do R&D," Aithadi says. "We made high- resolution characters for the rest poses, and then every fi ve frames for eight seconds, a modeler remodeled the blend- shapes with the same topology. When the bodies over- lapped, we created blends as if they were the same object. We had 10 or 15 modelers die during the project," he adds with a chuckle. Once modeled, animators used special rig- ging to drive the way the blendshapes worked. To control the skin and cloth textures, the team rendered 15 versions of the animated characters, including one with everything made of skin, another with everything made of velvet, and a variety of lighting passes. But, they also ended up blending the textures in 2D. "I know I should have taken this artwork and thought about it before loving it so much," Aithadi says. "And I did love it. It is so beautiful. But, that's why we like to work on Potter. The effect is very different—a bit of something new." –BR The digital stadium for the Quidditch tryouts is not yet draped with large pieces of cloth, so MPC needed to build every post and beam that you can see behind Harry Potter and Ginny Weasley. Apparating Sucks

• Cover