FROM a distance "The Polar Express" might look like just another holiday movie. Adapted from a much-loved 1985 children's book by Chris Van Allsburg, it is the story of a nameless boy living in a 1950's American suburb whose crumbling belief in Santa Claus is bolstered when, one snowy Christmas Eve, a phantom steam train pulls up in front of his house and a kindly conductor invites him to take a ride to the North Pole.

With Tom Hanks again starring under the direction of Robert Zemeckis - as he did in "Forrest Gump" and "Cast Away" - "The Polar Express" sounds as safe as safe can be, guaranteed to warm hearts and sell tickets.

But there is a revolution hiding inside this seemingly innocuous family film, to be released by Warner Brothers on Nov. 10. The first star-driven film to cross completely over to the digital domain, it might change the way movies are made and seen. Whatever critics and audiences make of this movie, from a technical perspective it could mark a turning point in the gradual transition from an analog to a digital cinema. And though the transition may not be as dramatic as the shift from silent to sound prompted by "The Jazz Singer" in 1927, it may have equally significant consequences.

Neither a traditional live-action film nor a computer animation of the kind Pixar has perfected with "Finding Nemo" and "The Incredibles," "The Polar Express" is something in between, a film that brings a true human presence into a virtual world by digitizing flesh-and-blood actors as well as the environments they inhabit. In the process it does away with many of the most basic elements of filmmaking: there are no expensive sets to be built, no elaborate lighting to be rigged, no bulky camera to be painstakingly hauled into place. In fact, there is no film. "The Polar Express" will touch celluloid only at the final stage of production, when the completed feature is transferred, by laser printer, from computer hard drive to film stock.

"To everyone's credit at Warner Brothers, they were taking a giant leap of faith on this," Mr. Zemeckis said during a recent trip to New York. "It's really tough for anybody to get their head wrapped around it."

For one thing, Mr. Hanks plays five roles, ranging from a 7-year-old boy to Santa Claus. Not all of these characters look like Mr. Hanks, but they all contain the spark of his individuality. The world of the film is manifestly the world of Mr. Van Allsburg's beautiful oil and pastel illustrations, a nocturnal landscape punctuated by soft forms and warm lights. But Mr. Hanks, along with the other members of the "Polar" cast (including Michael Jeter, Peter Scolari and Nona Gaye), has not been simply superimposed on a painted background. He has been absorbed into the lushly detailed images, almost as if his DNA had been digitized along with the landscapes. It is a cliché to say that a film looks like a painting come to life, but applied to "The Polar Express" that old phrase contains a new truth.

Whether the audience can wrap its collective head around this approach to filmmaking is only one of the many questions posed by a new technology that turns the director into the god of his own virtual universe. Will the new techniques finally make it possible for directors to be the sole authors of their films, in the way painters control their paintings or novelists their novels? Or will the unprecedented control eliminate the creative turmoil of what has often been called the most collaborative of art forms? Will the revolution serve the goals of storytelling and personal expression, or will it lead to an obsession with trivial detail and pointless perfectionism? Will actors embrace the challenge of playing against themselves in multiple roles, as Mr. Hanks does in "Polar," or will they become digital puppets, manipulated by unseen others? Will the new powers liberate visionary filmmakers, or will they make movies even more vulnerable to the whims of studio executives, who will be able to endlessly second-guess directors?

Long a pioneer in special-effects technology (in films like "Back to the Future," "Who Framed Roger Rabbit" and "Death Becomes Her"), Mr. Zemeckis sees promise and danger.

"It was wonderfully freeing," Mr. Zemeckis said. "This was like, well, I think we'll have the train come off the tracks and skid across a frozen lake. All right, great. Let's write that."

But, he emphasized, the technology must take the back seat. "It's still about story, as wild as it can be, or as simple as it can be," he said.

"To write a screenplay under these conditions takes some getting used to," added William Broyles Jr., who wrote the adaptation with Mr. Zemeckis. "Usually, as the time for filming approaches, you adjust your screenplay to what is possible. But with this, as the time approached, it became clear than anything was possible. At first, there was an incredible exhilaration, but then that was followed by the realization that anything you imagine has to be in the service of the story."

To watch "The Polar Express" in process and onscreen is to begin to understand the promise of the new technology and its potential drawbacks.

There was little that resembled a traditional shoot at a warehouse in Culver City, Calif., where the film was being made in April. In place of a soundstage, there was a domelike structure built of scaffolding that surrounded a playing area roughly 10 feet square. Attached to the scaffolding were several dozen infrared sensors, which could pick up and digitally record the light bounced back by the dozens of small reflectors on Mr. Hanks's black bodysuit, as well as by the 150 smaller reflectors attached to his facial muscles. With his face dotted by the tiny jewels, as the crew called the reflectors, Mr. Hanks looked like the pincushion man from the "Hellraiser" series. But after a few days of working with the reflectors attached, he said, he no longer noticed them.

"All I really miss are the costumes," he said. "I have to remember to touch the brim of a hat that isn't there."

When Mr. Hanks entered the playing space - "the volume," as Mr. Zemeckis likes to call it - his movements were recorded by a computer as points of light floating in a dark three-dimensional space. Even in this raw form, the connect-the-dots figure moving on the computer monitor was recognizably Mr. Hanks. It walked like him, gestured like him and, most important, crinkled and smiled and frowned like him.

Filmmakers have been able to capture full-body motion for some years using a process called mo-cap, in which a computer scans sensors attached to a performer's limbs and records the broad outlines of movements. "It's been around a long time from video games," Mr. Zemeckis explained. "They put sensors on the athletes for sports games and things like that."

The great leap of "The Polar Express" came in the ability to capture facial expressions: "When we did the first tests," Mr. Zemeckis said, "we had Tom do the body acting, and then we put him into a space where he sat in a chair and had to re-act everything from the neck up. I said, 'You can't do a movie like this.' So they went back and were able to figure out how to get both sets of sensors working at the same time. And once we started the movie, the technology kept getting better."

Steve Starkey, a producer of the film, calls the process "performance capture," because it records more than simple movement. There is individuality and emotion in that blur of swirling dots, and it becomes the job of the computer animators - in this case, people at Sony Pictures Imageworks, led by Mr. Zemeckis's longtime visual-effects supervisor, Ken Ralston - to retain that individuality while shaping the clouds of dots into the Boy, the Conductor, and the other characters.

The process falters, however, when it comes to the characters' eyes. Because of the impossibility of attaching sensors to the actors' pupils, eye movements must be animated independently, and they aren't always as convincing as one would like. The greatest commercial risk of "The Polar Express" lies in betting a reported $160 million budget that audiences will still be able to make an emotional connection through these somewhat glassy orbs, windows to the soul that seem slightly veiled.

The raw human figures - so bulky and balloon-like before they are refined that the animators call them Michelin Men - are dropped into 3-D spaces that have also been created in the computer by groups of designers and programmers. Mr. Zemeckis relied on longtime members of his team, including the production designer Rick Carter ("Forrest Gump") and the costume designer Joanna Johnston ("Who Framed Roger Rabbit") to do their usual work, though this time, instead of being built or sewn, their designs were constructed in the virtual environment.

"For example, for the big square at Santa's village, the art department designed it, and they did it just like they do a movie, except it goes one step further," Mr. Zemeckis said. "They conceptualize it, they draw blueprints, they build models, and then, once we sign off on it, they go and they build it virtually in the computer, just like architects do now for previews and that sort of thing."

Now, the real fun begins. With his 3-D characters inside a 3-D environment, the filmmaker has a literally infinite choice of camera angles. He can place his virtual camera at any point in the 3-D space, much as players of video games, like the newly released "Sims 2," can do, though the games have a a restricted range of positions and much less detail. He can move the virtual camera in any direction, simulating pans and tracking shots, and even a jittery, hand-held effect. He can simulate the look of any known lens (as well as some unknown ones, as the extraordinary deep-focus effects in "Polar" attest). He can alter the lighting at will, dropping in shadows and highlights that would take hours to reset on a traditional shoot. Instead of having actors sitting in their trailers, waiting for the crews to set up the next shot, they can stay on stage and in character and go straight from one scene to the next. And as Mr. Zemeckis pointed out, he also eliminated the risk and bother of working with child actors, substituting the skill of one consummate professional who has the only acting credit in the film's advertisements.

The process also promises a new level of exhibition. In a first for a major studio feature, "The Polar Express" will open both in conventional theaters and in a 3-D Imax format in some cities, including New York. "And all we had to do was run it through the computer again, just flip a switch and put the parallax in," Mr. Zemeckis said. "It's all 3-D already, so boom, it's just there."

All of these wonders come, inevitably, at a price - and not just the financial cost, which at the moment exceeds even the $1 million-a-minute average of Pixar-style animation. "In the next couple of years," Mr. Zemeckis said, "part of every film's process is going to be to adjust the images. And it'll be to change the color of an actor's tie or change the little smirky thing he's doing with his mouth. Or you can put in more clouds or move the tree a little bit. And that will be part of your normal film finishing process, where your image will be perfected."

Sometimes, though, it is the imperfections that make a movie come alive. Back in the 1910's, when movies were beginning to be filmed in studios rather than in streets and parks, D. W. Griffith famously worried about losing "the wind in the trees" - the sense of the aleatory that makes film seem spontaneous and real. Is faultlessness really a goal?

Mr. Zemeckis said that he believed that the technology's promise outweighed the risks of any early excesses. It is so radical that it has actually solved problems that came with the last breakthroughs in digital magic, he said.

"I found in my big effects movies where I had to do a lot of major blue-screen work, like in 'Contact' and in 'Forrest Gump,' it's really hard to keep the energy from flattening out, because the first thing that happens is the actor now becomes a prop if you're not careful," he said. "It takes a lot of discipline for the director and the actor to rise above the tedium of doing this blue-screen work, but there's none of that here. Performance capture is different because it's all about the acting. Without the tyranny of hitting marks and leading the lights and worrying about the boom shadow and your makeup and your wig and the line on your wig and all that horrendous stuff that stifles an actor's performance. Or when they do the greatest take ever and they miss the focus.''

"You could actually hire a director just to go out and work with the actors,'' he speculated, "and then you'd take the raw material back. But if he didn't do it exactly the way you wanted it, you could change it. And you could get it the way you wanted without actually having to stand there in front of the actor and convince him to do it your way.''

But that digital dream could also have a nightmarish underside. Imagine a movie without any physical reality, without any human presence or warmth. Imagine, in effect, even less personal versions of the coldly corporate digital-effects blockbusters that now dominate the summer.

Mr. Zemeckis acknowledged that danger but argued that he had already learned to overcome it: "What we did with 'Polar Express' was what we do now in music without anyone ever thinking about it. We have sophisticated digital sound equipment that can create any sound, and you can manipulate a note, sustain it, shorten it, change it.

"And we haven't replaced any musicians,, because the musician comes in and puts the emotional warmth into the performance. He sits at a keyboard and he just basically plays, but he puts that human emotional warmth in there. Then that goes into the booth and it's expanded and layered and all those textures are put on it. But basically what's there is there."

Mr. Zemeckis concluded: "So now what we're doing is the same thing, but for visual performance. The actor lays it down and then you just add things onto it or take away from it - whatever fits the story. That's how I look at it in a positive way."