When the film based on Chris Van Allsburg’s delicate and haunting children’s book “The Polar Express” plays in its own backyard, it has the purity of virgin, new-fallen snow. And most parents and children will be enthralled and enchanted by the positive themes it promotes.

But since the narrative-spare 32-page picture book’s journey is an interior one, found in the hearts of its readers, a cinematic story line was invented that often feels discordant, derivative and contrary to the tale’s simple pleasures.

Call it “The Polarizing Express.” This film about a young boy’s Christmas Eve train ride to the North Pole must travel down twin tracks.

One track is fidelity to source material whose through-line is a belief in the unseen, and which has become a holiday perennial for countless families. The other track is the digital technology called “performance capture” that helps imagine this journey.

When these two elements work together in the early scenes, everything feels comfortable and right.

Director Robert Zemeckis, who co-wrote the film with his “Cast Away” screenwriter William Broyles Jr., finds fresh perspectives on what already exists: a moonlit silhouette of falling snow, a hissing radiator, a lock of a mother’s hair falling in her face as she bends to kiss a child, light through a keyhole, marbles falling from the torn pocket of a child’s robe.

And what he invents, like a boy sliding across the ice in Roy Rogers slippers or a snowman wearing oven mitt gloves that move in the breeze as if to wave goodbye, are the sorts of intangible and almost imperceptible details of which the illustrator Van Allsburg might surely approve.

But once the boy is invited onto the train by the conductor – a digital Tom Hanks, who appears as five characters, including the boy and Santa – the film starts down a slippery slope into blandly familiar territory.

There are three songs – an over-the-top production number, a cloying ballad and a rocking greeting card from an elf that looks and sounds like Steven Tyler; superfluous characters, including a hobo and a Mutt and Jeff pair of engineers; and various emergencies that add a sense of urgency to originally contemplative material.

Santa is introduced with pomp and circumstance and urges his reindeer on with a neon whip.

Just imagine the outrage from readers if scenes, characters and devices were created out of whole cloth and inserted into films based on the similarly beloved “Harry Potter” books.

Throughout, the traditional digital animation – if that’s not an oxymoron – adds a liquid dimension thick as hot chocolate to Van Allsburg’s original images. And even devices created for the film, such as a train ticket floating through the countryside or the engine stopping inches from the nose of a caribou, have a poetry that fans of the book will recognize as being faithful to it in spirit, at least.

Although Zemeckis is best known for live-action films, he has experimented with animation and special effects throughout his career, in “Forrest Gump,” “Back to the Future,” “Death Becomes Her” and “Who Framed Roger Rabbit.”

But this is his first purely animated feature, and it is crafted with care and skill.

3 stars

Cast: Tom Hanks, Michael Jeter, Peter Scolari, Nona Gaye, Eddie Deezen, Charles Fleischer

Behind the scenes: Produced by Steve Starkey, Robert Zemeckis, Gary Goetzman and William Teitler. Written by Robert Zemeckis and William Broyles Jr. Directed by Robert Zemeckis.

Rated: G; jeopardy, mildly intense scenes.

Approximate running time: 100 minutes

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(c) 2004, Milwaukee Journal Sentinel.

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AP-NY-11-09-04 1716EST