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Behind the blue screen

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Like a magician’s top hat, this summer’s movies have yielded a dazzling array of spectacular trick effects, allowing moviegoers to vicariously share such thrills as a stroll along the red vistas of Mars (Total Recall) and the sight of a Wild West locomotive that flies (Back to the Future Part III). Two of the season’s blockbusters feature two of the most talked-about spectacles. In Die Hard 2, a terrified Bruce Willis skyrockets out of an exploding plane, and in Ghost, Patrick Swayze stands eerily and calmly still as a train speeds through him.

Both those scenes were done via the blue-screen process, a technique that involves filming an object in front of a solid blue screen — the color that’s easiest to remove later — and then combining it with various baakgrounds to create a composite.

Special-effects supervisors Micheal McAlister and Bruce Nicholson from Industrial Light and Magic, the post-production facility responsible for both scenes, illustrate, step by step, how Bruce emerged unsinged from a ball of fire and how Swayze firmly stood his ground.

In Die Hard 2, Bruce Willis, as try-harder cop John McClane, finds himself in the worst fix of his perilous career: trapped in the cockpit of a grounded plane while hand grenades fall all around him like lethal hailstones. Thinking fast, Willis sees an ejector seat, straps himself in, and blasts off, rocket-like, seconds before the aircraft blows. Here’s how it was done.

ILM’s McAlister and a 40-person live-action crew assembled in Southern California’s Simi Valley to blow up a one-fourth-scale model of the aircraft with liberal amounts of jet fuel and gunpowder. ”We did it perfectly in a one-shot deal, but it takes a lot of figuring beforehand,” explains McAlister, who needed five hours to set up the entire explosion scene. To capture the upward motion of the plane’s fireball, he rigged safety-shielded cameras atop a large construction crane for both close-up and wide shots.

Six weeks earlier, Willis — secured in an ejector seat taken out of a plane and rigged to a motorized contraption — had been filmed in front of a blue screen at the ILM studio in Marin County, as he turned slowly head-over-heels and rotated as if on a turntable. Willis was a ”real trooper,” says McAlister. ”After shooting all night in Lake Tahoe, he drove straight here and worked all day with us.” The biggest challenge of the ejector seat shot was to have Willis first appear very small, then come right up to the camera, larger than life. This was achieved by having the camera travel down a 100-foot-long dolly track and by speeding up the film to make his topsy-turvy spinning ascent look faster.

After one month of intense work with optical printers, this composite image, merging the exploding plane and the blue-screen shot, was completed. First the optical printers removed all traces of the blue background, leaving Willis dangling alone. Then a Willis-shaped silhouette — called a matte — was made and superimposed onto the explosion footage, to block out the part that Willis would occupy. Finally, the two sequences were assembled like a high-tech sandwich.

In the romantic thriller Ghost, Patrick Swayze is Sam Wheat, a novice dead person desperate to communicate with his earth-bound girlfriend. To do that, he must track down a surly specter (Vincent Schiavelli) who stalks the subways and can help him master his new and still puzzling spiritual skills.

In this scene, Swayze stands on a subway platform and leans his head into an oncoming train, scanning the inside of the cars as they appear to roar straight through his face.

”To the audience Sam looks like a normal human being, but in fact he’s an apparition,” says ILM’s Nicholson, who spent seven and a half months working on 50 of these ”pass-through” shots for the film. ”In order to show that, we make this solid character move through solid surfaces.”

On the blue-screen shot of Swayze, the actor’s physical talents were an asset. ”Having a dance background, Swayze has a really good sense of where to put his body in space and how to put it in a position necessary for the camera,” Nicholson says. ”It was pretty remarkable.”

In New York City, two months earlier, Nicholson and his three-person crew assembled footage of a speeding subway car and a stand- in leaning into the open door of a stopped train. That created the position to be filled by Swayze’s blue-screen shot. Intricate measurements of the camera position were also taken at that time so that the correct perspective could be duplicated exactly when photographing Swayze.

To create a realistic effect, the crew had to solve the problem of the train’s windows. There had to be a now-you-see-his-face-now-you-don’t effect, as the transparent surfaces and solid doors passed alternately through him — a difficulty that ”we didn’t get into until we started to composite and saw that something was wrong,” says Nicholson. This first matte, created by blocking out the blue background, will indicate Swayze looking through a window while the subway rushes by. The second matte indicates Swayze minus the part of his face that would be obscured when he passed through solid metal. ”We developed the strategy so that it would be dropped or used depending on what was passing him,” explains Nicholson.

On the completed composite, Nicholson says, the alternating surfaces were ”an additional enhancement to make the entire effect a bit more believable. It’s sort of a subliminal thing that when somebody sees the film they don’t say, ‘Hey, that’s neat.’ It just kind of works psychologically to make it a more convincing shot, so someone won’t say, ‘Oh, that’s fake.”’

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