LOS ANGELES -- Tom Hanks used experimental technology to morph into a little boy, a train conductor, a hobo and Santa Claus for the new Christmas adventure "The Polar Express."

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Video On Demand: Bob Shaw Talks With Tom Hanks About 'Polar Express'

This is how he was able to co-star with himself: The two-time Oscar-winner climbed into something like a black wetsuit lined with neon-blue streaks and a tight cap, and had hundreds of glistening white specks on his face. Computers recorded his movements and expressions, which were then transposed onto his various characters.

With just a few more technological evolutions, "The Polar Express" may change the way people consider performance -- actors no longer would be constrained by their own bodies.

Harrison Ford could be 80 and still playing a young "Indiana Jones." Sean Connery could play himself circa "Dr. No" in a new James Bond movie. Jack Nicholson could star as a 16-year-old, and Haley Joel Osment could play a geriatric.

Actors could swap and trade digital bodies: Tom Cruise could perform as Humphrey Bogart; Julia Roberts could try Rita Hayworth. Or Eddie Murphy could easily play every character in a film -- old, young, heavy, skinny, white, black, male, female -- without any makeup or prosthetics.

"The Polar Express" director Robert Zemeckis, renowned for using state-of-the-art effects in his films, including the "Back to the Future" trilogy, "Who Framed Roger Rabbit" and "Cast Away," said the breakthrough came about four years ago when Hanks sent him a copy of the slim, beloved 1985 children's book by illustrator Chris Van Allsburg.

The actor wanted to see if it could be made into a film.

"I looked at these beautiful paintings and said, 'It's great but how are we going to do a movie like this?"' Zemeckis said. "We thought about it, and thought about it and realized the emotion of the book was in the paintings. The story was really interesting but the paintings are what made that book so popular.

"We never thought it was appropriate for 'The Polar Express' to be an animated cartoon," Zemeckis added. "And to do it live action would not be absolutely true to the emotion of the book. So we came up with this process that we called performance capture. It's digitally rendered, but there's no animation."

By that method, he said, they were able to create the soft pastel imagery of Van Allsburg's book through computer technology but the characters were not manipulated by animators to coincide with the actors' voices, as in such films as "The Incredibles" and "Shrek."

Hanks was familiar with that kind of work from playing Woody the cowboy in the "Toy Story" movies: he recorded lines, then left the body to animators.

"This is not one of those movies," Hanks said. "Everything you see (in 'The Polar Express') performed by a human being was performed by a human being on a soundstage."

The sensors on Hanks' suit and face were recorded as he moved around a mostly vacant room, and those gestures and expressions were layered with a digital skin that moved in relation to the actor.

"There's no reason to do a movie like 'Mystic River' this way," Zemeckis said, referring to last year's effects-free, gritty drama that won Oscars for Sean Penn and Tim Robbins. "But there is the chance now to let imagination run wild."

Motion capture computerization became familiar to most moviegoers when actor Andy Serkis controlled the movements of Gollum in "The Lord of the Rings," and it's a common technique used on sports figures like Tiger Woods to animate their own moves in video games.

But the subtleties of human expression are so delicate that most eye, mouth and face movement traditionally have been left to animators, who frequently work from tapes of the actors.

"The Polar Express" pushed the technology into a new dimension by mapping the areas of Hanks' face with 152 sensors, so his instinctual movements control the faces of his characters.

"Believe it or not, the information would extend to a computer so you could tell the difference between a frown and a smile, eyes wide open, essentially every nuance that the human face can go through," Hanks said.

Occasionally one of the BB-sized sensors would fall off, Hanks said, which the computers rendered as if Santa's cheek or eyebrow suddenly stretching down to touch the floor.

Computer animators did come into the scene, however, to "take what we did and turn it into a little boy outside with snow falling down," Hanks said

Three other adults play children in the movie -- Hanks' "Bosom Buddies" co-star Peter Scolari, "The Matrix Reloaded" actress Nona Gaye and Eddie Deezen, the nerdy character actor who was Eugene in "Grease."

"It was ridiculous amounts of fun," Hanks said. "You just kind of have to forget an awful lot of stuff that you know as an adult and take part, literally, in the recess atmosphere."

Some movie critics have complained that the human characters in "The Polar Express" continue to have a plastic, lifeless quality compared to actual flesh and blood performance -- which suggests filmmakers still have a ways to go before pure imagination acting becomes practical.

One sticking point in the process that couldn't be fixed in "The Polar Express" was Hanks' voice.

While Deezen and Gaye supply their young characters' voices, Hanks and Scolari are dubbed by child actors. Zemeckis said he tried digitally altering the pitch and tone of Hanks' voice to play the boy, but couldn't make him sound like a believable child.

It's Hanks' movements and expressions, but Daryl Sabara -- the curly haired star of "Spy Kids" -- supplied the voice.

"The visual aspect of movies is beyond imagination," hanks said, "but the sound is pretty much the same as in (Al) Jolson's time. "