Issue link: https://digital.copcomm.com/i/119349
CG Characters the ground, and Crawe runs. Bryan [Singer] wanted the giant to look at Crawe as if he were an ant running away. He waits. One, two, three beats. Then smacks him to the ground. Because it is the introduction to the giants, the camera goes from far away right up into his face and focuses on an eye. It's raining. He has wet hair. And water runs off his skin surface. We had to push our texture maps to 32k on close-ups and shift back dynamically so we could see pore detail and detail in the eye. We added hairs on the skin to add subtle details. And had water dripping off." It was one of many shots in which the camera moves close to a giant's face. "Their faces are 40 feet across," Rosenbaum says. "We had to be diligent about how we handled the skin shading and eye development." tech papers written over the last several years on skin shading," he says. "We developed a new approach that handles multiple layers of translucent materials." Rosenbaum explains that usually subsurface scattering utilizes a single-layer approach. Light hits the surfaces, diffuses uniformly, and produces a homogenous look on the skin surface. "That's why skin often looks like silicon or honey or milk," he says. "But skin is more complex. It has multiple layers. Dermis, epidermis, fat, muscle. All that affects light differently, so you need to build multiple layers of the scattering algorithm to account for the photoreal look." For rendering, the crew settled on Arnold (Solid Angle) in combination with Katana (The Foundry) rather than RenderMan (Pixar). The only live-action element in this scene is the actor, barely visible, inside the cage. Digital Domain artists created the CG giants and the digital environment. The conceit was that an evil king had formed the giants from earthen materials. In early designs, the giants looked like mud men. In later designs, they became more humanoid, but with dirt, straw, bits of grass, and other earthly materials embedded in their skin. "One thing that made the show difficult was that each of the principal giants had a unique look," Rosenbaum said. "We couldn't steal or borrow from other characters. We could start with a base-level skin shader, but beyond that, we had to start each character from scratch. They had different textures and different earthen materials embedded in their skin. And, they're 24 feet tall, so they had a lot of surface area. We had to get the shading on their skin and eyes right." Realizing the team would need to develop a new technique, Rosenbaum plunged into a research project. "I pulled out a bunch of the "RenderMan 16 wasn't out yet," Rosenbaum says. "The big advantage with Arnold was that it was a true global illumination solution with a real raytracer, so we could get precise lighting representations on the characters, including the eyes. The eyes were really key on this movie because they were four times the size of a human's eye and often close up. Previously, we had to cheat the shape for shading purposes, but we didn't have to cheat now. We reconfigured the eye to be anatomically correct." There were disadvantages, though, too. "The disadvantage is that raytracers are slow," Rosenbaum says. "We had fewer iterations, but each render took longer. The other drawback was with displacement. There were quite a few instances where we needed to displace the surface, so we had to come up with a clever approach. In RenderMan, we would have gotten micropolygon displacement for free." On location, HDRIs and light probes helped the team match the light when the giants were in live-action scenes. "Most of the big scenes, though, were digitally created environments," Rosenbaum says. "So we would take the HDRI from the previous scene, adjust it slightly for the time-of-day shift, and use that." Digital Effects Supervisor Paul Lambert spent time before principal photography making sure the HDRIs captured on set matched the Red Epic camera. "It was one of the first shows to use that camera," Lambert says. "Everything was brand new at the time. So, we would shoot with the Epic camera and with our Canon 1Ds, which we use with the HDRIs, to make sure everything calibrated." Lambert also discovered a way to make sure that when the camera moved into the sun, they had the correct values. "When you go to all the trouble of getting a physically correct renderer, you want the correct values," he says. "Up to now, when we captured an outside HDRI, the camera couldn't go far enough to capture the exposure of the sun, so we knew it would be clipped and we would compensate for it. Paul Debevec came up with a technique to put a filter in the back of the lens to capture the sun, but on set we don't have time to change lenses." So, the Digital Domain on-set crew used two cameras. One captured environment HDRIs. Another was a 150mm camera that was stopped down with a massive filter. "We would point it at the sun, get the exposure, take it into [the Foundry's] Nuke to correct for characteristics we had worked out, and then put the sun value into the HDRI," Lambert says. "It meant we had to move to 32-bit EXR – in a lot of shots, the sun value was 80,000 and 16-bit EXR only goes to 65,000 – so we had bigger files." To determine those characteristics, Lambert spent time on a rooftop with the filtered camera. "I took a picture of the sun every hour," he says. "I got a good amount of data and a sunburn." But, it was worth it: "Knowing we had the correct values meant we could tune shaders knowing they would be correct. You wipe out a lot of cycles of trying to interpret." And the Beanstalk In several shots, Digital Domain's giants interact with a giant beanstalk created at MPC. The giants' weight affected the beanstalk, and the movement of the beanstalk affected their performance. "It took a tight collaboration," Rosenbaum says. "What made it work was the relationship with Greg Butler [visual March/April 2013 CGW0313-Jackpfin.indd 27 n n n n 27 3/14/13 12:15 PM