Four years back, Tom Hanks and Robert Zemeckis took a bungee jump with ''Cast Away,'' gambling that audiences would line up to watch Hanks talk on and on to a volleyball. The happy result: $234 million in domestic grosses and Hanks' fifth Oscar nomination. Now the star and director are again leaping into the unknown -- abetted by ''Cast Away'' screenwriter William Broyles Jr. -- with an all-CG version of Chris Van Allsburg's 1985 storybook about a boy whisked away by train to Santa's native land on Christmas Eve. ''You couldn't do this live-action,'' says Zemeckis. ''I mean, you could, but it would be the most expensive film of all time, and it still wouldn't look right.''
Looking ''right,'' for Zemeckis, meant meticulously emulating Van Allsburg's somber, painterly illustrations, which have helped the book sell more than 5 million copies. To find the cinematic equivalent of their slightly eerie vibe, Zemeckis turned to a still-evolving branch of CG technology called ''performance capture'' and pushed it in new directions on a reported budget of $165 million. ''It's not animation. It's real,'' says Zemeckis of the result. The actors were filmed on bare soundstages with their faces and bodies covered in reflective dots. Cameras picked up the dots as points in space, then transposed the actors' movements directly into CG figures (which should look all the more vivid in a 3-D IMAX version scheduled to open the same day as regular prints).
Hanks' old ''Bosom Buddies'' costar, Peter Scolari, plays a kid called ''lonely boy,'' while Hanks became a computer-age Peter Sellers by acting out multiple virtual roles. He's immediately recognizable as the mustachioed train conductor. But he's incognito doing the movements for the doubting little boy, the boy's father, a spooky, broken-nosed hobo (a role the producers initially considered pitching to the late Marlon Brando), and Santa Claus himself. Says Hanks of his five-role tour of duty: ''The only thing that threw me is there's no costumes to play off of. You wear them one day so they can digitize them and laser-scan them -- but that's it. You gotta pretend.''
WHAT'S AT STAKE Hanks' chance to chug into holiday-blockbuster territory à la Jim Carrey in ''How the Grinch Stole Christmas.'' But is he as appealing in newfangled CG as he might be in old-fashioned makeup?