“All aboard!” goes the conductor’s cry in “The Polar Express,” and sure enough, after the holiday kidpic earned $60.3 million of its $297.5 million global take on Imax 3-D, more films have been quick to follow in its tracks.

“When you realize that you can do double-figure millions of dollars on a movie that’s already been out in theatrical exhibition with no ads, that’s a big deal,” says “Polar” producer Gary Goetzman.

Four of the seven titles on Warner’s Imax slate this year are 3-D pics, including two new CG-animated movies, “The Ant Bully” and “Happy Feet,” that originally went into production as traditional 2-D projects.

Sony will also release its first animated pic, “Open Season,” day-and-date in Imax 3-D.

“After ‘Polar Express,’ the studio came to me and asked if I’d be interested in doing the movie in

3-D,” says director John A. Davis.

” ‘Ant Bully’ is really perfect for Imax: the idea that the audience gets shrunk down to the size of ants, gets eaten by frogs, fights giant wasps.”

As for “Happy Feet,” the pic serendipitously features a cast of animated emperor penguins — the same animals made popular in last year’s Oscar-winning docu “March of the Penguins.” The film tells the story of Mumbles, voiced by Elijah Wood, who doesn’t fit in because he can’t sing, but makes up for it by dancing.

“I predict it will be a record-breaking Imax DMR release,” says Imax prexy Greg Foster.

But the real proof of the format will be the first time Imax demonstrates 3-D on a live-action feature.

“We used to go to people and say, ‘Don’t shoot your movies in 35 mm, shoot them with our

really bulky, expensive, high-quality cameras. You’ll be happier for it,’ ” Foster says.

Of course, Imax found filmmakers were reluctant to deal with the added cost and hassle of using its equipment. So the strategy changed. “We’re a technology company,” Foster explains. “Let them do what they do: They make movies. Let us do what we do: We have technology.”

The new philosophy led Imax to develop not only its patented DMR technology, which remasters Hollywood features shot on 35 mm so they can be shown on Imax screens, but also a new 2-D-to-3-D conversion process.

Imax prepared a test reel with scenes from “Spider-Man 2” and “Harry Potter and the Goblet of Fire” in which the superhero swings between buildings and the boy wizard flies a hippogriff into the aud.

“It’s very effective and helps make the film even more of an event,” says “Harry Potter” producer David Heyman. “Initially, we had conversations on ‘Potter 4’ about isolating a few sequences (in 3-D), but we didn’t have the time to do it.”

“The first time that we do 2-D to 3-D will be revolutionary,” Foster says. “I think 2007 will be the year.”

Meanwhile, the technology is far enough along that Imax seamlessly applied it to a few scenes of its nature doc “Deep Sea 3-D” that had been shot in 2-D.

But Imax isn’t without competition in the 3-D field. George Lucas has partnered with In-Three to convert all six “Star Wars” films into 3-D, and Disney embraced Real D technology to screen “Chicken Little 3-D” in theaters with digital projectors last fall.

James Cameron says his next feature, a sci-fi pic called “Project 880” due out in summer ’08, will feature a 3-D mix of live-action and motion-capture effects. It will be shot with thecustom stereoscopic camera system he developed while filming underwater Imax docus “Ghosts of the Abyss” and “Aliens of the Deep.”

“I personally am over Imax,” says Cameron, who favors the lower print cost and higher screen count digital offers. “What I would hope to do with my films is (play) the Imax venues in addition to the digital venues if the cost analysis supports it.”

Like Cameron, “Polar Express” director Robert Zemeckis has committed to releasing his next motion-capture pic, “Beowulf,” in 3-D. However, producer Steve Starkey says it’s too early to say whether it will open in Imax or on digital screens, the way Sony plans to release “Monster House” this fall.

Still, Foster believes Imax’s 3-D format offers the same advantages over the megaplex experience as its 2-D product — bigger screens, greater detail, enhanced sound. “What’s good for 3-D is good for Imax because we are the premium 3-D experience,” he says with confidence.