Computer Graphics World

August 2009 22 n n n n CG Characters•Stereo the camera crew creates the stereo cameras and puts renders in front of me, the light- ers reproduce the other eye for all the CG objects and creates the stereo render of the plate, and the painters clean up the prob- lems. e thing that's different is that we have to fill holes if anything has been cut out of the plate." As they would with any visual effects pipeline, the stereo 3D artists started with the matchmove of the plate that the "flat- film" team had generated, which gave them a virtual world—rough geometry representing what was filmed on location as seen from the point of view of the cam- era used on the set—with the CG animals positioned in that virtual world. "en, we added more detail to the matchmove model that the 2D team didn't have to think about," Engle notes. "Some- times the 2D team only matchmoves a 2D surface, like a table, so if a guinea pig is on the table, we'd add other objects. And, we had to fill any holes." Once they had filled the holes, which often happened on a per-shot basis, they created a stereo pair of virtual cameras in the computer and rendered images for each eye. "For CG objects, it was easy," Engle says. "We'd just render the other eye to create the stereo pair. To make the plate itself 3D, though, the easiest way to describe it is that we projected the plate photography onto the geometry in the virtual world and took a picture from the other point of view." New Stereo Techniques When the camera was at guinea pig level, the artists tuned the stereo depth to what a guinea pig might see. "Guinea pigs' eyes are on the order of a couple centimeters apart," Engle says. "Humans' eyes are six to six and a half. So, we tended to keep the cameras close together, especially when [the guinea pigs are] in a terrarium, to make the environments feel real." e artists also developed new ways of working with the stereo image to heighten the experience. "e 2D release is a wide- screen, 2.40 format," Engle says. "But the studio also wanted a 1.77 format for high- definition home video. So we decided to take advantage of the extra information for the 3D version. e theaters are projecting the film as if it's 2.35, but we're delivering 1.85 with letterboxing on the top and bot- tom, so it looks square-ish. But, every once in a while, we allow objects to extend into the letterboxed region." To the audience watching with 3D glasses, it looks like the objects are coming out of the top and bot- tom of the screen. "One of the shots in the film is of a snake trying to attack a guinea pig," Engle says. "e point of view is from the guinea pig behind a sheet of glass. e snake rears up, coils, strikes, and hits the glass with its jaws wide open. It's a great 3D moment. We let the jaw go over the top and bottom of the 2.35 picture so it literally feels like the snake is in the audience's space. Breaking the mask this way allowed us to have an overt way of saying, 'is is in your space,' without bringing objects out into the space and having the audience's eyes cross." In 2008, the film Journey to the Center of the Earth broke new ground by becoming the first to incorporate CG visual effects in a live-action film shot with stereo 3D cameras. G-Force breaks a second barrier. "Rather than shooting the film in 3D, we added the stereo in postproduction," says Engle. "is is the first time that a live-ac- tion film integrated with CG visual effects has been converted to 3D." By using visual effects techniques to create the stereo version of the film, Imageworks discovered new ways in which directors and cinematographers might want to create deeper worlds: Rather than using stereo 3D cameras to film the action, they can contin- ue working with the less-limiting and more- familiar systems. Whether or not they have superagent CG guinea pigs as stars. "I think the way we ended up doing the conversion gives filmmakers a lot of flexibility," Stockdyk says. "If they have a new movie coming to the table and they're thinking about stereo and live action, I think they have to consider the extremely efficient way we did it." n Barbara Robertson is an award-winning writer and a contributing editor for Computer Graphics World. She can be reached at BarbaraRR@comcast.net. When the guinea pigs meet Hurley (above) in a pet shop, the animators performed them as if they were real animals, not secret agents. A snake attack, one of the most interesting stereo 3D effects in the film, takes place in the pet shop.

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