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MillimeterAnimated Performance
Nov 1, 2007 12:00 PM, By Ellen Wolff
Sony Pictures Imageworks goes for a more live-action style in motion capture.
Simultaneous facial and body capture helped produce integrated mo-cap performances for Ray Winstone, Anthony Hopkins (top) and Angelina Jolie (bottom).
If the devil is in the details, Imageworks animators and texture artists had several demons to wrangle. “Creatively, we had to reach a level of detail where we could make the world of Beowulf feel believable enough so you could watch the story,” Chen says. “We're not trying to fool people into believing this was photographed. It's a fantasy world. We thought we'd stop much earlier in terms of stylizing it. But it looked like the skin needed to be more realistic. We also got to the point where we wanted to see hair coming out of King Beowulf's ears to make him more interesting.”
Simulated hair and clothing were handled with Maya, but atmospheric effects such as dust, smoke, and snow were done with Side Effects Houdini, and this challenged Imageworks to develop a hybrid pipeline that included significant proprietary software. Nowhere were these challenges more evident than in the simulation of fire, which is plentiful throughout Beowulf. “Everything in this movie is lit by fire,” says Sony visual effects lead Vincent Serritella, who co-developed the fire simulation used on the film. “This story takes place before electricity, so we had hundreds of fire sims of candles, torches, and fire pits.”
The original development on this system had been done for Imageworks effects in Ghost Rider, which had a character made of fire. “That was supernatural fire,” Serritella says, “but we've been able to leverage 75 percent of that pipeline. For Beowulf, we wanted the natural integration of how fire transitions to a carbon, where fire lights the smoke and the smoke blows around. Now the fire sits in space when it lights the smoke. And we took our fire rendering a lot further, using a volumetric rendering approach rather than the [Pixar] RenderMan approach that we did on Ghost Rider.”
Imageworks began by importing matchmove or environment data into Houdini, and the team did what Serritella calls “field building.” The graphic artists would literally paint the places they wanted fuels for the fire, indicating which areas they wanted to burn and where they wanted collisions to happen. “If we wanted fire to wrap around a character, we'd have the character itself be a collision object. Then we'd write that data out to disk and use Maya's fluid solver engine,” Serritella says.
The Imageworks fire-simulation system uses concept of simulation boxes, each of which has parameters that a particular piece of fire is simulated within. This method gave Chen and Zemeckis the ability to specify if they wanted ambient wind affecting the fire, for example. “If they wanted wind coming from the left, everyone working with smoke, fire, and embers would have their wind direction pointed that way. We could make a wind tunnel for our boxes and add turbulence to the sim,” Serritella says.
“Each piece of fire had a voxel space around it, basically little 3D pixels,” Serritella says. “If you have a tight, conservative box, you'd clip the fire and it would stop sharply along an invisible wall. So you give enough padding to let your temperature heat up and then fade appropriately. We'd strategically get the lay of the land for a shot, map out what's going to be on fire, and, based on our boxes, set up an automated process to dice up the scene.” This helped optimize the rendering process, which was done in Svea, Imageworks' proprietary volumetric renderer.
“Beowulf pushed the scale of using a volumetric renderer. If you have a volumetric solution, it's a true 3D render of smoke. So you could rotate a camera around it, and it will look like a 3D object. If you have lighting that rakes across it, you get to feel the parallax of the light as the camera moves around it,” Serritella says. This approach gave Imageworks compositors a lot of control. “If they wanted to do a pseudo-camera-depth blur in the background, they could do that. It really was a playground of effects.”
So is Beowulf, in the end, an animated movie or an effects movie?
Jerome Chen has a simple answer. “It's all these things. Why does one have to preclude the other?”
