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This fall, “Frankenstein” will come to life in more ways than one.

Just as director Kenneth Branagh’s take on the Mary Shelley classic hits movie theaters in November, bookstores will be flooded with two versions of the story: the 1818 original and a new paperback edition based on the screenplay, known in the trade as a novelization.

Call it what you want, it’s still big business.

With novelizations, “you tap into a market of book buyers who are maybe not reading The New York Times Book Review but are readers and are looking for something they’re familiar with,” says Peter Borland, head of the film and TV division at Signet Books. “Usually they have seen the movie. The other market we tap into are merchandise-driven movies like `Batman,’ where the book becomes almost a collectible.”

Leonore Fleischer, who has written the “Frankenstein” novelization and more than 50 others, says people buy them “to extend their experience, and because they’re readers. It fleshes out the characters, it’s a favorite movie, and they want to know more. Why do people buy soundtrack albums?”

But there’s a big difference between soundtracks and novelizations: The books, which have been around for more than 20 years, have long been considered literary bottom-feeders, little more than cheap merchandising ploys. Though publishing houses now try to get experienced genre writers for these projects, quality is still hit-or-miss.

“Certain novelists can bring an added depth and freshness to a story based on a film,” says Irwyn Applebaum, president of Bantam Books. “Others just do a bare-bones fleshing-out.”

When it comes to selling books, however, literary excellence is a secondary concern; box-office gross is all-important. “If the movie does not do well, it’s very unlikely your book will do well,” says Borland, who adds he is “pleased” with sales of more than 100,000 copies of any title.

A monster success like “Dracula,” released in both classic and novelized versions, sold 800,000 copies (the tie-in did better than the Bram Stoker original). And Fleischer says her novelizations of “Rain Man” and “Benji” have had worldwide sales of 1 million and 3 million copies, respectively.

Not that Fleischer, or any other writer, is becoming rich off these knockoffs. Authors are paid a fee of $5,000 to $20,000 and earn no royalties. They also work under extreme pressure.

Because novelizations are based on screenplays, writing cannot begin until final script approval, which often occurs shortly before a film goes into production. Authors are hired by studios or publishing houses, then given from two to three months to write the book.

Sometimes, it’s less than that. Fleischer says she pounded out the tie-in for “Junior,” an Arnold Schwarzenegger film due out in November, in two weeks. “Benji” was written in a 48-hour marathon.

Fleisher says novelizers enjoy the challenge of turning a skeletal framework into a fleshed-out story. “A film has closeups or music to tell you (it’s) suspenseful or romantic,” she says. “A novelizer has words, and you don’t want to say only `He smiled,’ `He frowned.’ You have to establish a mood in words, a feeling and response in words without closeup or montage.”

What’s in it for the writers?

“There’s both exposure and the opportunity to stretch yourself,” Applebaum says. “It’s the challenge of working with another group of characters, to bring more information and background to” the story.

Applebaum’s company, Bantam, has spearheaded a new novelization trend: It published a hardcover version of “Philadelphia” that had respectable sales of more than 40,000 copies. This stab at upgrading the tie-in’s image will be given a boost by Hyperion’s November release of “The Crossing Guard,” based on a Jack Nicholson movie. The tie-in was penned by Tony Award-winning playwright David Rabe (“Streamers”).

But publishers are not convinced that the Rabe work will improve the genre’s reputation.

“They’re not review-driven books, they’re not considered literature,” Borland says. “They have a more merchandiser-product air about them.”