Long before Samantha Barks was awarded ragamuffin Eponine in the cinematic “Les Miserables,” she had grown up seeing the tuner numerous times, and went on to essay the part in the West End and on the star-studded 25th anniversary gala broadcast. Yet despite all her previous familiarity with the property, nabbing her movie debut sent her promptly to the Victor Hugo novel.

Kristen Stewart was first dazzled by “On the Road” as a high school freshman, and later “slapped that thing on my car dashboard, I was so into it.” For all that, getting cast as the pic’s complex, flamboyant Marylou — the love interest of both Sal Paradise and Dean Moriarty — led her right back to Jack Kerouac’s now canonical text.

They aren’t the only actresses with recent occasion to catch up on Great Books required reading. With Barks, Anne Hathaway and Amanda Seyfried passing around Hugo’s weighty tome between “Les Mis” takes, Helena Bonham Carter would have had time to switch to Dickens in anticipation of Miss Havisham in “Great Expectations.” And soon, scores of Oprah’s Book Club fans will decide whether Keira Knightley meets their image of “Anna Karenina.”

Knightley has admitted in past interviews that her perception of the Tolstoy novel changed from the first time she read it while filming “Atonement” at age 21 and found it “incredibly romantic.” Revisiting the tale in summer 2011, just before filming began, she “didn’t find it romantic at all” but instead saw it as “much darker, and the question of whether Anna Karenina is the heroine or the anti-heroine was a huge one. And that’s the definition of a classic is that it changes as you change.”

Not all adapters are eager to see thesps like Knightley leap back to the original prose works. William Nicholson, who shepherded the “Les Mis” through-sung libretto to the screen, is torn: “An actor needs all the support she can for understanding the role, so I would never say she shouldn’t read the book. On the other hand, the role we screenwriters — and in this case, the show writers — wish the actor to interpret is the one in the script, not the one in the novel.”

The necessary quality, Nicholson says, is “restraint,” bringing enough taste and judgment merely to pick up background without engendering a round of insistent questions: “Why haven’t you included this line, or this beat?”

To “Great Expectations” scribe David Nicholls, it depends on the nature of the adaptation. With a loose, freewheeling take on the tale, “it’s best to stick to the script,” but Mike Newell’s new film set out to reflect great faithfulness to Dickens. Moreover, to cut past preconceptions built up by previous Miss Havishams, Nicholls “was very happy for Helena to read the book. … She had a lot of notes on physical details, little quirks that she picked up.”

One quirk, the scribe had forgotten: Dickens’ character is “only partially dressed when she hears the news that she’s been jilted at the altar, and she has this single shoe on her foot. Helena loved that detail and incorporated it into her performance.”

Barks put her homework to good advantage as well. “Eponine is a slightly different girl in the novel, and after the read I tried to intertwine those two characters. I wanted to combine the heart we all know from the stage show, and the darkness and awkwardness of the novel, where she comes from a much more twisted world.”

Sometimes source material can plant a single, fertile seed. “There’s an image from the book, ‘a rose in misery.’ And it’s a visual that’s in my head whenever I think of her, a way of saying she’s a diamond in the rough.”

As Knightley became more immersed in Tolstoy’s massive tome, the more she became convinced that the author seemed to have a love/hate relationship with his title character. “She’s duplicitous, she’s deceptive, she’s cruel,” Knightley told a British talk show hostess, “and yet she’s also kind and loving and honest at exactly the same time.” And it’s that kind of complexity that drew her to the role.

Stewart, for her part, relied heavily on two volumes, both the Kerouac fiction and Gerald Nicosia and Anne Marie Santos’ “One and Only,” a nonfiction portrait of Neal Cassady’s real first wife, Lu Anne Henderson, leaning on extensive audiotapes (to which Stewart also had access).

To the thesp, Marylou possesses “a bottomless pit of life in her. She’s very vivid, she’s just fun. She’s got that type of personality you want to run after, you want to keep up with someone like that. And I think that’s sort of what ‘On the Road’ is all about, it’s finding those people and letting them push you, and seeing if you can push back.”

Stewart reminds us of literature’s power to influence not just an artistic endeavor, but a life. The novel, she says, “made me a little nostalgic for a world I never lived in. This is something everybody probably says, but it’s just so true: I loved how big the country felt. I felt like I could have it. And the roads may have changed, but what they’re talking about is still what life is all about. I lived there. And it blew my mind.”

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