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n n n n Motion Capture card that we put in the set." The lighters would choose the number of rays to bounce inside the set based on the ma- terials in each robot, optimizing the lighting and rendering based on, particularly, glossiness. "The glossier the material, the fewer rays that we needed," Palop says. "If you have a mirror, you only need one to have a perfect reflection. When you have more diffuse surfaces, you want to sample more to reduce your noise." The crew rendered each robot separately Camera operators on location could see CG robots in their viewfinder overlaid on the live-action stream in order to accurately frame close-ups, such as the one at top, and medium shots, such as the one at bottom. Digital Domain created the robots in these final images. each sequence and each robot. We could par- tially automate the way we could switch on levels of damage through a sequence." To create the robot surfaces, the artists de- signed more than 30 different materials, some based on photographs of real objects, some imaginary. "For the black robot Zeus, we wanted something that looked slick and cool, but couldn't find photographic reference," Palop says. "So, we created a few layers of clear coat and carbon fiber, and put a bumpy sur- face beneath with a specular component. It was really cool, but not necessarily anything that's really out there." The effects department added the fluids and sparks using Side Effects Software's Houdini for hydraulics and other fluids, and Maya fluids to create dust and dirt. "We baked out geometry for some of the effects," Palop says. "We would render fluids out of Maya using [Mental Images'] Mental Ray, but if we had geometry—say, Noisy Boy's arm—we'd use Houdini and V-Ray." V-Ray, however, did the lion's share of the rendering. "We set up a test between [Pixar's] RenderMan and V-Ray, and ended up going 24 October/November 2011 with V-Ray," Palop says. "It was giving us a better look for the robot. We probably could have gotten there with RenderMan, but it would have taken more time, and we had an- other show going on that needed the Render- Man TD support more than we did. So V-Ray made sense, and it turned out to be a great ex- perience. The crew on Tron had done a lot of the work for us. We basically grabbed the best features of the Tron lighting pipeline and used those on our show." The survey crew that had been on location brought back photographs and HDR probes that gave the lighting crew information about every main source of light on set that they needed to match. "We had geometry based on the survey data of the set, and we could pro- ject photographs taken on set onto the geom- etry to have an accurate representation of the set," Palop says. "We gave that to the lighters. They'd bring the robots into this virtual envi- ronment and have V-Ray start rendering. We had photographed every light source using a fish-eye lens with dynamic range. We knew its location and how intense it was. Then we put the HDR onto cards; each light source was a to have absolute control over the rendering. When two robots fought, they'd render the two together to have accurate reflections and shadows from one onto the other, but with only one visible at a time. "One of my favorite memories involved our lighting and surfacing teams, which were re- ally special," Nash says. "We were in Detroit. I think it was in August, about nine weeks after shooting our first robot sequence. The team at Digital Domain sent me a shot, a first pass out of lighting that blew me away. I looked at the shot and said to Swen [Gillberg], 'What do you mean first pass? I don't have any notes.' Then I walked up to Shawn [Levy]. He smiled. He could tell I had something to show. When he saw the robots, he went bananas. He showed the shot to everyone on set, and it was a boost for the whole crew. We had the practi- cal robots Legacy had built. And, we had the guys in green spandex with tracking markers. But for the most part, we had Simulcam with nothing to look at. So it was good for the crew to see what the robots would look like. We fi- naled some of our early shots while we were still in Detroit." Despite his excitement and pride in the look of the robots, though, Nash believes the coolest thing about this show was the process. "The whole process worked beautifully," he says. "Because we were involved from the be- ginning, we had ownership and full member- ship in the main unit team. It was an incred- ibly smooth production, a very tight ship, and hugely collaborative." These teams from Digital Domain, Giant, and Video Hawk moved the Avatar process out of Pandora and into the real world. By in- serting CG creatures into the middle of a live- action shoot, the director and camera operators could work as if the CG creatures were there on location outdoors and indoors. And that means visual effects had taken one more step out of postproduction and into production. n Barbara Robertson is an award-winning writer and a contributing editor for be reached at BarbaraRR@comcast.net. . She can Computer Graphics W orld

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