Computer Graphics World

September 2009 18 n n n n CG I•Stereo movies, we needed to dial in shadow bi- ases. And when we transferred our lighting rigs from one scene to another, the results were more predictable." e trick was in knowing when to stop. "If we turned the knobs too high and in- creased the sampling too much, it was easy to turn a four-hour render into a 16-hour render without any appreciable increase in quality," Bredow points out. Because Arnold renders entire scenes each time it renders, to give the lighting team the ability to work interactively, the Arnold crew created a system in which they rendered a first pass at low resolution with low anti-aliasing. "is gave the lighters a way to quickly show me the lights blocked in," says Kramer, who spent much of his time during production sitting in a dark room and giving comments on lighting ef- fects, cloth, and hair. "e artists had eight-core machines," Kramer says. "So, we could load in all the geometry and move lights in near real time. e next level was 1k resolution with better anti-aliasing. en, if we liked that, we'd go to full resolution and full quality." One of the problems the group ran into, however, was in rendering hair. When the s trands of hair became too fine, the ray- tracer had sampling problems. "We'd get lots of chattering," Kramer says. "So Rob [Bredow] came up with a control so the hairs would never be smaller than the size of pixel." Once the characters moved away Senior CG supervisor Grant Madden Anderson, who had last worked on Beowulf, took on the role of stereoscopic supervisor for Cloudy with a Chance of Meatballs. While some stereo films these days are using depth subtly, this film provided the perfect settings for stereo gags. "This is a fun movie, so we could bring objects into the audience," Anderson says. "You don't want to do too much of that, but audiences seem to like it, and it can be fun. We had food falling, being thrown, exploding. It's the very nature of this film, and also a personal preference, to have things coming out into the audience. It was like being in a food fight. It was a blast." The first scenes in the film, before Flint invents a way to turn water into food, are flat, and then as the film progresses, the scenes get deeper. "We have a shot at the end where Flint is holding onto the machine for dear life while it's shoot- ing food out the bottom," Anderson explains. "We pull his legs way out into the audience, and you wonder whether he'll make it or he'll fall. It added to the sense of peril." Working with Anderson was a small team of assistant technical directors and camera artists who helped manipu- late the left-eye and right-eye cameras to give the scenes depth and the characters roundness. "Basically, we create two 3D cameras and dial two pa- rameters: convergence and interocular," Anderson details. Convergence, which describes how cameras are angled, determines the depth. If you angle the cameras in, objects push back. If you angle them out, objects push forward. In- terocular, the distance between the cameras, stretches ele- ments within a scene and, thereby, makes characters look rounder, especially ones close to the cameras. The stereo operators usually start with an interocular distance of 2.4 inches, the average space between human eyes. "Generally, we'd dial in the interocular to get the round- ness we wanted, and if that moved objects too close, we'd tweak the convergence to shove them back," Anderson says. "If objects are too close, it's painful. You can have only so much depth, close or far away, before it becomes too deep, so we tried to maximize that stereo budget to use it to our best advantage for every scene and still have the scenes cut together well. At the very end of the movie, we did an overall tweak of the convergence to make the scenes fit to- gether better." As is the case for most stereo postproductions, the Cloudy Animators used a flexible rigging system to create background characters from generic models. The studio's version of Arnold rendered the colorful, highly saturated scenes. Fun with Stereo

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