With their third feature film, Laika has quickstepped stop-frame animation into heady new worlds. Cheesebridge, the film's location, is a Victorian-era town with quirky buildings, cobblestone streets, a town square, and a castle-like Guild Hall where snooty, rich, cheese-obsessed aristocrats and the Cheese Guild's "White Hats" meet.
One would-be White Hat, the red-hat wearing Archibald Snatcher (voiced by Ben Kingsley), has convinced the citizens of Cheesebridge and the White Hats that Boxtrolls steal their cheese and snatch their children. His chief evidence, such as it is, is a baby's disappearance. His goal: to become a White Hat.
The Boxtrolls, harmless dumpster divers and mechanical tinkerers, are strange little creatures that live in the sewers and wear cardboard boxes around their middles. Their names are the labels on their boxes: Fish, Shoe, Oil Can, Fragile, Specs. They didn't steal the baby, they rescued him; the baby grows up wearing a box labeled "Eggs."
When Eggs meets Winnie, the ruling White Hat's daughter, the two become determined to set the story straight. The result is a madcap action/adventure story with Snatcher chasing Eggs and the Boxtrolls over rooftops, through the streets, and into the sewers. Boxtrolls has more action, more characters, and a larger environment than usually seen in a stop-motion film.
"We're taking a hard look at this magical medium and trying to do different, exciting things," says Steve Emerson, visual effects supervisor. "A big part of that has been embracing CG technology. Our philosophy is moving forward while looking backward. We respect the craft for what it is and then take a supplementary role. They make their magic on the stages, and we fill in the gaps."
Emerson notes that Laika shot Coraline, the studio's first stop-frame film, almost entirely in camera. With ParaNorman, the studio's second film, CG artists helped the directors open up the stop-motion world. The Boxtrolls takes the notion further.
(top) animators combine face parts printed with a 3D printer to create characters’ expressions. (bottom) VFX artists remove the seam lines for final shots.
"We did a lot more on this film than in the past," says Eric Wachtman, look development lead. "We have more backgrounds and set extensions, and the complexity is greater. On ParaNorman, we had a handful of [CG] buildings and houses. On this film, we had 20 or 30 rendered at character level with displacement, paint, roof tiles. And the complexities of the characters' costumes went far beyond what we did for ParaNorman."
As with ParaNorman and, to a lesser extent, Coraline, the hero puppets' faces are printed from CG models using a rapid-prototyping system based on 3D Systems' printers. Animators create expressions by combining printed mouth and brow parts (see "Face Forward," August/September 2012). In addition, the stop-frame department heads rely on artists in the visual effects department to extend their world.
During the course of a stop-frame production, animators typically position the puppets on 50 active stages, but it isn't enough. To determine what Boxtrolls needed, Emerson sat with the department heads early in the process as the group broke down the script.
"I sat back and stayed quiet to see what they could pull off on the stages, in the model shop, and the puppet department," Emerson says. "When they ran out of resources, everyone in the room turned to me."
The hero characters are always real - there are no digital doubles for the live-action puppets that star in the film. And the focus of a shot is real. But, the sequences often called for more characters than the puppet department could handle.
"For crowds, we typically build the first and second rows physically," 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-prototyping department.
Animators performed CG crowds that matched the stop-frame motion of the hero characters in the foreground.
"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 different because we had to maintain consistency 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 metal 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 puppets. 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.
During the production cycle, while the puppet department and art team crafted the physical puppets, the visual effects 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 department to see where and how they layered it, and why they made those decisions."
The hair on a physical puppet is complicated because stop-frame animators must be able to move pieces of it and have those pieces hold that position until they move it again.
The CG department created hair and cloth for the CG extras that matched the puppets’ hemp hair and laser-cut fabric.
"It's not hair," Wachtman says. "It's made of hemp that's spray-painted, super-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 [Pixar] PRMan DSO (dynamic shared object) for [The Foundry's] Katana that let us interpolate those curves into strips that added approximately 200 hairs; we rendered ribbons, not curves. We textured them to give the front and back sides different colors."
Similarly, the physical puppets wear costumes carefully crafted to look appropriate 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 template 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, separate control masks. The shader read that in. We built up the layers that way. We could plug in a color and tell it what kind of fabric, and the system would figure out how to make the cloth."
Dancing with Puppets
Some of the most complex work by the CG animators and visual effects artists centered on a ballroom scene during which elaborately dressed and coifed aristocrat caricatures danced with and around similarly elaborately dressed and coiffed CG extras.
"When we saw the animatics, we knew the amount of animation, choreography, and resources would be daunting," Emerson says. "We had to be sure that by the time the animators were ready to animate, we knew where every pixel was supposed to be."
In the film, Eggs, Winnie, Snatcher, the White Hats, and the aristocrats dance among a crowd of dancing CG extras. To help the CG and stop-motion animators, Laika brought in professional dancers to work out the choreography and camera moves for the sequence.
"The live-action shoot with real dancers was a first for Laika," Emerson says.
CG extras and set extensions helped make the town of Cheesebridge seem larger and more densely populated.
But, the real choreography helped the team manage the complex interaction of real puppets and CG extras. "They'd all be dancing together in the scene," Emerson says, "crossing forward and behind one another. So, we made sure that if a practical puppet changed partners, it danced with another puppet. And when Snatcher runs across the floor pulling up the bottoms of dresses, we made sure that was physical."
Animators worked from motion-captured data taken from the professional dancers. They altered the performances to match the motion of stop-frame characters and adjusted each dancer's position to make the poses work with caricatured aristocrats who are not professional dancers. Thus, they started with real motion that they tweaked to match real stop-frame motion.
"It all starts with the practical," Emerson says. "The CG extras, the effects, the environments, all the work we do always starts with the practical."
Many live-action films have CG atmospheric and natural effects - smoke, fog, dust, debris, fire, and so forth - to amp up the action, and often those CG effects are enhanced with practical elements layered in during compositing.
The visual effects team on The Boxtrolls did something similar, adding fog, steam, dust, debris, and fire to plates shot on the physical stages. The difference is that their natural phenomena needed to match those in a caricature of the real world. The practical elements the CG artists layer into particle simulations are photographs taken in the stop-motion art department.
"The geniuses in the modeling and rigging departments across the street build effects, like water with glass and lighting," Emerson says. "We do literal interpretations of what they do on stage and then work to enhance and make those effects more effective. The thing with particle effects, though, is that they are difficult to animate one frame at a time."
When Winnie runs outside to retrieve a hat she's dropped from a window, the fog in the streets plays an important role.
"We worked with the art department to define what the fog would look like, and with the camera team to learn how they would approach fog practically," Emerson says. "If you look hard at our fog, you'll see little pieces of hand-woven cheesecloth. The camera team photographed elements for us - the cheesecloth - that we took into Nuke's 3D system and distorted, and animated the elements until they felt integrated. The cheesecloth gave the fog that handmade feel."
The process fits into that philosophy Emerson calls "looking forward by looking backward."
"We can make amazing CG fog systems in Houdini, but we also look backward," Emerson says. "We bring in the photographed, handmade elements. If we had only shot real fog, it may have helped tell the story, but we wouldn't have had that extra level of attention to detail."
CG artists extended practical sets shot on stop-motion greenscreen stages.
To create clouds, the CG artists worked in Side Effects Software's Houdini or with matte paintings. In either case, they would combine the resulting images in Nuke with photographs of practical clouds created on set in the art department with various materials.
"On the physical set, they would set up sky units, animate the clouds, shoot them as tests, and we could use those to build the CG clouds," Emerson says. "In-house matte painters also created a lot of the skies and clouds in CG. But, they were all painted by hand first."
Smoke, which the artists largely generated in Houdini, became a character in its own right. "The Red Hats and Snatcher have their own, inky black smoke," Emerson says. "So we went through a whole development cycle for the smoke."
And where there's smoke, there's fire, which was a more volatile problem. It's difficult to make practical fire that looks real enough to be believable in a scene. Yet, fire was important in the climax of the film.
"Fire is a tough thing here," Emerson says. "For Coraline, we hand-animated the fire and took it into compositing -[Apple's] Shake back then. For Boxtrolls, we had a mixed bag. We wanted to make sure the fire hit the mark in terms of style and vision, but if it was too stylized, it didn't immediately read as fire. It needed to tell the story, to feel tactile, and look cool and feel threatening. But, it couldn't be distracting."
The effects team ran simulations in Houdini and photographed real fire. They grounded the style with 2D animation drawn one frame at a time, and used that to mask off and create shapes. Then, they worked with the elements in Nuke and integrated their fire into the live-action plates shot with the puppets on the stages.
"It's all about the shapes and the artistic language of the film," Emerson says. "If you're working on a traditional film with visual effects, you want to make things photoreal, and there are many tools that make it possible to do photoreal effects. Animated films, on the other hand are stylized and not necessarily photoreal. The biggest challenge for us is that we're both."
As do visual effects artists working with plates filmed on sets for live-action features, the CG artists on The Boxtrolls needed to add photoreal effects to plates filmed on live-action sets. But, the photographed real worlds the Boxtrolls artists had to match were as stylized as the digital worlds in an animated film.
In a stop-motion film, all the locations are miniatures, designed to scale for the approximately foot-tall puppets. To expand the puppets' world beyond the stages, the visual effects team extended the sets using CG buildings, streets, and props.
"We build to the same scale," Wachtman says. "It's a little weird to get used to. You have to retrain your brain to not build life-sized things. But once you start working on the buildings in context, it works itself out in your brain. At the end of the day, we try to make everything feel like it's the same-world scale."
As with the characters, CG modelers working on environments "fill in the gaps" in the scenes.
"We build the next layer back, the horizon, and the sky," Emerson says. "It's the same as everything else. If we can get something in camera, we will. If they have the resources to build the sets, they will. But, when they run out of set, we step in."
Here, a stage set is enhanced with CG props, extensions, and atmosphere.
When sets built in the art department are ready for the stage, the crew photographs the environments on turntables to keep as reference. The CG modelers use those photographs as reference for the digital set extensions.
In one sequence, for example, the Red Hats chase after Eggs, who leaps off a wall, lands on the red-tiled rooftops, and rides the rooftops down like a roller-coaster. "In a scene like that, we look at how much we can build digitally," Emerson says. "We start with anything the puppets touch and anything in the immediate environment. Beyond that, it's up for grabs. The rooftops where the tiles get knocked off are physical buildings, but beyond that first layer, it's a CG world."
CG buildings and props also expanded the market square, particularly in the climax when a giant, complex, and fantastical machine - a "mechadrill" - stars.
"We built lots of barrels and boxes," Wachtman says. "Random stuff. We'd scan the practical props on the sets, clean up the scans, and use that data. We didn't have to do much hand modeling. But, we built a digital mechadrill, and couldn't use scans for that. It was a beast with a lot of moving parts. We shot a ton of reference in controlled lighting. Then we built and textured it piece by piece."
Modelers and texture artists create hero buildings to enlarge the stop-motion world. Matte painters add sky and animated clouds.
And, the CG extras were put to work for the climax, as well.
"We have a lot of Boxtrolls and puppet extras in the market square," Emerson says, "more CG buildings, as well. A lot of CG work. Hopefully, people can't tell."
Opening the World
All told, approximately 60 artists worked in the CG department, many of whom repaired plates and touched up the puppets' faces to remove the lines between the mouth and brow parts, work that visual effects 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 different work from anything anyone has seen before. For me, that's the most exciting thing about Laika."
Barbara Robertson is an award-winning writer and a contributing editor for CGW. She can be reached at