Animating Atmosphere

The wispy fog that drifts through so many Hammer horror movies was one of the trickiest elements to create for The Curse of the Were-Rabbit, and according to visual-effects supervisor Paddy Eason of The Moving Picture Co. (MPC), the filmmakers “did it pretty well every way we could.”

The challenge was to create swirling mist that would not look like plate work. “We were unsure of what was possible in post when we began prepping the film,” recalls Were-Rabbit co-director of photography Dave Alex Riddett, “so we experimented with various stop-frame techniques to produce a believable fog effect.” After ruling out fog filters, Riddett and co-director of photography Tristan Oliver “did many tests using gobos to project cloud shapes onto swatches of background gauze, and that produced a random, varied fog pattern that was controllable frame by frame,” says Riddett. “However, these only worked as distant effects — in fact, a vestige of this animatable fog can be seen in a distant track in to the medieval church early in the picture. Achieving close-up fog effects seemed possible by passing a glass plate with various levels of spray-on diffusion — typically hairspray or just greasy fingerprints — in front of the lens. But when we were shown what MPC could add to our footage, we were happy to give them free rein to create their own magic.”

Eason’s relationship with Aardman began during his tenure at the Computer Film Company, where he was the digital-effects supervisor on Chicken Run, and he immediately understood that Were-Rabbit’s fog effects should achieve a slightly stylized realism. “The look of everything in the Wallace & Gromit films is really quite tactile, with an emphasis on realistic lighting,” he observes.

The filmmakers determined that combining animation plates with fog plates filmed at live-action speed would be their best bet. The next task was determining what would look like mist at model scale. “We first experimented with dry ice, which looked ridiculous,” says Tom Barnes, Aardman’s technical director. “Then we began testing smoke machines, and we finally hit on one that chilled the smoke as it came out. Until we found that, the smoke would just disappear off into the top of the studio, and it had so much movement that it looked completely wrong in scale.”

“Smoke has a mind of its own,” notes Oliver, “so in order to get continuity from shot to shot, you’re looking for a density that works and a degree of movement. You need several takes to get it right because it’s such a random thing; if it’s hot outside, all the smoke is heading to the ceiling; if there’s the slightest draft in the studio, the smoke will be on the move. Trying to hit a point at which the smoke is the right density and has some movement but not a lot of movement means you do take after take after take.”

The technique for creating most misty scenes was to load the camera with Fuji Super F-125T 8532 and film the animation on a clean set (or against greenscreen), then shut the set down and fill it with smoke, switch to Fuji Super F-500T 8572, and film the smoke at 24 fps, match-moving the shots using motion control. “On the fog pass, the smoke hung in the air nicely as the camera moved through it,” says Eason. “Our task in those instances was to get a matte for the animated character and insert the character into the foggy scene; the matte was pulled from the greenscreen if they gave us a greenscreen pass, or it might just be rotoscoped.

“But that approach wasn’t always possible because they didn’t always shoot fog plates. In some cases, we created our own fog using generic fog elements that the cinematographers had shot against a black backdrop, along with various live-action effects elements we’ve gathered over the years like smoke and dry-ice mist. We’d layer those into the scene to make it appear as though the set was full of fog.” He adds that it didn’t matter how the live-action smoke was lit because it was almost transparent. “Fog is a strange, abstract thing, and it doesn’t really reveal lighting in any particular way when you’re shooting it as an element against black. As long as the backdrop remains unlit, it doesn’t matter whether the smoke is lit from the front, back or side.”

Given that the camera is often on the move in Were-Rabbit, layering in fog elements was only part of the compositing job, which was supervised by Stuart Lashley. “We had to give some thought to the three-dimensionality of it all,” notes Eason. “When there was an extensive camera move, we’d do a full 3-D track of the scene in Boujou and then add successive planes of fog elements that the camera could move through. That created a nice illusion of 3-D depth, even though we were using basic compositing techniques.”

When the were-rabbit had to race into the mist and leave a small vortex in its wake, the compositors gave the CG fog a nifty twist. “For most of those shots, we simply took successive planes of fog and applied little twirling distortions to the elements, doing offsets of a few frames each time,” explains Eason. “Even though it’s a 2-D technique, it feels like a 3-D effect. We did actually create fully 3-D fog for one shot and played around with fluid dynamics in Maya to create the swirling effect.”

The filmmakers couldn’t have been happier with the results. “We lived with the shots uncomposed for months and months — just a piece of animation shot against greenscreen with rigs in, and a series of plates of fog,” says Oliver. “Finally MPC would get their mitts on it, the greenscreen would come out, the rigs would come out, and suddenly the characters were in that environment, and it looked fantastic. It proves you can put CG into stop-frame and vice versa, and it’s quite seamless.”

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© 2005 American Cinematographer.