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www.postmagazine.com 23 POST OCTOBER 2014 Emerson says. "Everything beyond is up for grabs." Modelers working in Autodesk's Maya have physical puppets for reference and typically begin their modeling process with scans of a gray maquette. Working closely with the art, rapid-prototyping, and puppet departments, the modelers fit the CG extras into the same world as the real puppets, making sure that the CG faces look the same as those output with the 3D printers in the rapid-proto- typing department. "The scan data dictates the contours, crevices, and the surface of a digital puppet," Emerson says. "But because we don't have to worry about the same mechanics internally, the split lines, or the mechanics of the mouth bag, we can make surface textures that are uniform and perform correctly." Matching the physical puppets only goes so far. "Even though some of the final puppets might have a little thumb print, they try not to have that, so we don't add it to ours," Wachtman says. "We tried putting striation lines, like in some of the printed faces, but they looked wrong when we animated the faces frame by frame." To create crowds of Boxtrolls, the modelers built kits of parts that the animators could mix and match to create variations. The art department supplied unique labels for the boxes. "All the Boxtrolls had the same rig," Wachtman says. "And the topology of the boxes, arms, and legs was the same. But the topology of the heads was differ- ent because we had to maintain consis- tency with the RP (rapid-prototyping) department." In addition to the Boxtrolls, modelers built kits of caricatured humans — the aristocrats, workmen, and shopkeepers. "The males had consistent topology, but each female was unique," Wachtman says. Each stop-frame puppet has a met- al skeleton inside with joints that allow animators to position the puppet's body frame by frame, and the CG puppets have a similar rig. The CG rigs inside the digital puppets weren't identical to those inside the physical puppets, but they were representative. "You can do anything with a CG character," Emerson says. "But they don't have that option with the physical pup- pets. We gave our animators the tools they wanted, but we kept the digital rigs as simple as possible." The CG characters' costumes and hair, however, had to match the physical world exactly. HEMP HAIR During the production cycle, while the puppet department and art team crafted the physical puppets, the VFX team worked on the CG Boxtrolls and human characters. The human characters, which have hair and costumes, were the most complex. The puppet modelers gave the CG artists detailed descriptions of how they created the hair and how they applied it. "As they were discussing how to make the puppets, we were right there taking reference," Emerson says. "We didn't just make CG hair and lay it on our digital puppets. We worked with the hair depart- ment to see where and how they layered it, and why they made those decisions." The hair on a physical puppet is com- plicated because stop-frame animators must be able to move pieces of it and have those pieces hold that position until they move it again. "It's not hair," Wachtman says. "It's made of hemp that's spray-painted, su- per-glued, and wired. You can't put King Kong CG hair on our puppets. So, we made our own; we imitated in CG what they did." Wachtman describes the system they used: "It's similar to other hair systems and shaders," he says. "But, we couldn't use any shaders out of the box. We modeled patches for the curves. Then, we had a PRMan [Pixar's RenderMan] DSO [dynamic shared object] for [The Foundry's] Katana that let us interpo- late those curves into strips that added approximately 200 hairs; we rendered ribbons, not curves. We textured them to give the front and back sides differ- ent colors." Similarly, the physical puppets wear costumes carefully crafted to look appro- priate for the foot-tall puppets and that animators could move into position from frame to frame. The team tried projecting textures — photographs of the physical cloth — onto the CG puppets, but the result wasn't satisfactory. "The characters looked like they were in a game," Wachtman says. "They weren't believable." Instead, the CG team built a costume's shell in Maya, laying out the shell with appropriate UVs. Then, they created the cloth procedurally. "Sometimes we'd put a swatch of their cloth under a microscope to try to figure out the thread patterns," Wachtman says. "They were making fabrics, weaving a lot of crazy things. We had laser-cut fabric, tile fabrics. They'd do a basic cloth, cut a pattern, and then send it to the paint department. So, we did the same thing using co-shader layering." Wachtman explains: "We wrote a tem- plate that would take a weave pattern, the weft and warp, set the tension, and build the cloth procedurally in [Pixar's] Slim. Basically, we built a master cloth shader. Once we got the look of the cloth right, we painted on top and put that into a co-shader to get a different response. We did basic color painting, darkening, and detail in [The Foundry's] Mari." OPENING THE WORLD All told, approximately 60 artists worked in the CG department, many of whom repaired plates and touched up the pup- pets' faces to remove the lines between the mouth and brow parts, work that VFX artists have done on each of the three films. But, with this film, because the CG artists can create digital extras and environments that blend into the stop-motion world, they helped move that world into new dimensions. "We give [the directors] breathing room," Emerson says. "They get to pull the camera back and widen the shots. It comes down to telling the story they want to tell without restrictions. They have the freedom to open up the world and tell a bigger story if that's their choice. So, one of the wonderful things is that we can enable them to do more than they can practically. Beyond that, we're trying to do distinctive and differ- ent work from anything anyone has seen before. For me, that's the most exciting thing about Laika." Learn more about The Boxtrolls in the September/October issue of Computer Graphics World, Post's sister publication. All of the Boxtrolls had a common rig, which could be mixed and matched with varying parts. ANIMATION