LOTR in SPAAAACE

LOS ANGELES, Jan. 8 — James Cameron, the director whose “Titanic” set a record for ticket sales around the world, will join 20th Century Fox in tackling a similarly ambitious and costly film, “Avatar,” which will test new technologies on a scale unseen before in Hollywood, the studio and the filmmaker said on Monday.

The film, with a budget of about $200 million, is an original science fiction story that will be shown in 3D even in conventional theaters. The plot pits a human army against an alien army on a distant planet, bringing live actors and digital technology together to make a large cast of virtual creatures who convey emotion as authentically as humans.

Earlier movies like “The Lord of the Rings” series did this on a limited scale, as in the digitally designed character Gollum, whose performance came from the actor Andy Serkis, while others like “The Polar Express” have used live actors to drive animated images — so-called motion capture technology.

But none has gone as far as “Avatar” to create an entirely photorealistic world, complete with virtual characters, on the expected scale of the new film, Mr. Cameron said in a telephone interview.

“This film is a true hybrid — a full live-action shoot, with CG characters in CG and live environments,” said Mr. Cameron, referring to computer-generated imagery. “Ideally, at the end of the of day, the audience has no idea which they’re looking at.”

For its aliens, “Avatar” will present characters designed on the computer, but played by human actors. Their bodies will be filmed using the latest evolution of motion-capture technology — markers placed on the actor and tracked by a camera — while the facial expressions will be tracked by tiny cameras on headsets that will record their performances to insert them into a virtual world.

The most important innovation thus far has been a camera, designed by Mr. Cameron and his computer experts, that allows the director to observe the performances of the actors-as-aliens, in the film’s virtual environment, as it happens.

“It’s like a big, powerful game engine,” he explained. “If I want to fly through space, or change my perspective, I can. I can turn the whole scene into a living miniature and go through it on a 50 to 1 scale. It’s pretty exciting.”

Sam Worthington, a young Australian actor, has been named to play the lead, a paralyzed former marine 150 years in the future, who undergoes an experiment to exist as an avatar, another version of himself. The avatar is not paralyzed, but is an alien: 10 feet tall, and blue. Zoe Saldana, another relative unknown, has been chosen as the love interest.

The live-action shoot with actors will begin in April, with major effects being done by Weta, the filmmaker Peter Jackson’s New Zealand-based effects company, which created the effects for his “Lord of the Rings.” The film is scheduled for release in summer 2009.