The filmmaking process may not always be an art, but it is never a science. Too many intangibles militate against predictability. This year, contrasts dominate — with certain pics in given genres taking the long road to the screen and others achieving multiplex presence in near-record time.

Two films based on bestselling, critically acclaimed novels illustrates just how differently such projects can fare, even when top talent is involved. “Love in the Time of Cholera,” based on the Gabriel Garcia Marquez novel, failed to generate much enthusiasm despite a cast led by Javier Bardem, a screenplay by Oscar winner Ronald Harwood and helming by Mike Newell. Conversely, “Atonement,” based on Ian McEwan’s book, elicited some great reviews and received seven Golden Globe noms.

Though “Cholera’s” long gestation may not be responsible for its lackluster performance — the book dates from 1985 — “Atonement’s” appearance onscreen a mere five years after first arriving in bookstores might have spurred its success. Yet “Atonement’s” journey from page to screen was neither as smooth nor as predictable as such brevity suggests.

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Before falling into helmer Joe Wright’s reverent hands, “Atonement” was attached to director Richard Eyre and producer Robert Fox, who brought it to Working Title. “I can claim no credit for their initial work,” says Paul Webster, who ultimately produced the film, along with Working Title’s Eric Fellner and Tim Bevan.

In fact, Webster produced this project only because Eyre left to direct “Notes on a Scandal” and Fox also departed. After Wright was offered the director’s chair, Webster seemed a natural for producer since they had recently worked on “Pride & Prejudice,” another successful literary adaptation that, like “Atonement,” stars Keira Knightley.

Though Wright and Webster retained scribe Christopher Hampton from the original team, the screenplay was completely rewritten. “It had gone far from the novel,” says Webster, “and Joe wanted to return to that. He wanted to examine both the tragic love story and illustrate the creative process and the impact it can have. The challenge was to try to make the literary approach accessible.

It is an immensely satisfying book, but it does break

book, but it does break all the rules, as does the film.”

In some cases, a project’s duration is a question of perspective. Or so it seems looking at “Into the Wild” and “Charlie Wilson’s War,” two films inspired by nonfiction material.

On one level, “Into the Wild,” based on John Krakauer’s 1996 bestseller, reps producer-writer-director Sean Penn’s determined struggle to bring a pet project to the screen. But the full story is more complicated.

“Sean got interested about 12 years ago, when the book first came out,” says Art Linson, who produced the pic with Penn and William Pohlad. But because the family of the book’s protagonist, Christopher McCandless, was reluctant to see his story immortalized on the bigscreen, years of gentle prodding were required for Penn to get the go-ahead.

Once that happened, though, things progressed quickly. “From the time Sean and I bought the book to the making of the movie was just four or five months,” Linson says. “He wrote the script in weeks. Then he made a couple of revisions, the others joined, and the movie was off and running.”

The relatively quick screen transfer of George Crile’s “Charlie Wilson’s War,” first published in 2003, is practically ironic, for producers Tom Hanks and Gary Goetzman of Playtone are known for their deliberateness. “We’re the slowest production company in town, and proud of it,” says Goetzman.

Though he acknowledges this project’s relative swiftness, Goetzman maintains that speed was never an end in itself. “Our goal is to get it right,” he says. “However long it takes for the popcorn to pop, that’s OK with us.”

Of course, sometimes the popcorn doesn’t pop — or, put another way, attend the tale of “Sweeney Todd,” the pic based on Stephen Sondheim’s 1979 musical. Producers Neil Meron and Craig Zadan had hoped to bring this Grand Guignol property to the screen as a Tim Burton film, but though it is now in theaters with the helmer they envisioned, they are not the film’s producers — Richard Zanuck, Laurie MacDonald and Walter Parkes are.

“We’re the ones who interested Tim in it” says Zadan. “And we had a signed deal with Warner Bros. It was supposed to follow ‘Mars Attacks.’ But Tim sort of lost interest. What’s personally painfully is that he has come back a decade later, and we’re not involved.”

Yet Meron and Zadan are singing and dancing just the same — having produced “Hairspray” with John Travolta in drag. And while it took “Sweeney” a quarter century to land on the bigscreen, “Hairspray” made it just five years after opening on Broadway. Indeed, the musical is still running on the Rialto, its B.O. pumped up thanks to the movie’s branding of the title.

And that fast track might have been even faster had Travolta been more decisive. “He took 14 months to give us an answer,” says Zadan. “We thought it was the dress, but it was a question of getting the voice and the look right. The studio said, it’s been over a year; we should move on. But we said, he hasn’t said no, so we’re taking that as a yes. And we were right.”