The challenges of adaptation can be diametrically opposed: Boiling down a massive novel by the likes of Leo Tolstoy represents an entirely different proposition than does fashioning playable dramatic scenes peopled by real-life figures from a piece of journalism or historical biography; the first requires judicious editing and condensation, the latter imaginative re-creation and, almost inevitably, a degree of fictionalization. Fans of the literary perennials by Jack Kerouac and J.R.R. Tolkien have demanding expectations they might fear cannot be met by a film, while readers of a work as uniquely literary as David Mitchell's Cloud Atlas would have to accept going in that a literal adaptation would be impossible.

There are other issues. For instance, Tom Stoppard wrote his balanced and highly focused adaptation of Tolstoy's oft-filmed Anna Karenina before director Joe Wright decided to shoot much of it on deliberately artificial, theatrical sets; therefore, the writer can receive none of the credit -- nor the blame, depending on one's opinion -- for the film's overarching artistic approach

Meanwhile, whereas Stoppard succeeded at boiling down Anna Karenina to a two-hour miniature in which you can distinctly recognize the original, the screenwriters for The Hobbit: An Unexpected Journey set about something quite the reverse, expanding the first part of Tolkien's under-300-page novel into a film that runs nearly three hours and is merely the first of three -- heaven for fanatics, possibly too much for the general public.

If one has read Doris Kearns Goodwin's massively researched best-seller Team of Rivals: The Political Genius of Abraham Lincoln, it's clear that the book could only have been one of screenwriter Tony Kushner's many sources for his teeming Lincoln, which in all but official credit reads like an original screenplay. Similarly, the script that Lucy Alibar and Benh Zeitlin evolved into the basis for Beasts of the Southern Wild is based on just a small portion of the former's play and might most accurately be described as having been "inspired" by Alibar's play, so far does the film venture off.

When the source is a Man Booker Prize winner and has sold in the millions, the pressure on the screenwriter is greater than usual. David Magee has reflected everything that is essential about Yann Martel's novel Life of Pi and found a way to provide it all to director Ang Lee so as to make a nearly ideal representation of the novel. Most impressive is that they have retained the buoyancy of the novel's humor. Turning to another heavyweight, if Walter Salles' ambitious On the Road hits both high points and potholes, it's hard to say that Jose Rivera's adaptation doesn't do about as reasonable a job as one could imagine at condensing and paring down Kerouac's sprawling yarn.

Providing a contrast to these films based on celebrated literary sources is a tasty item that seemed to deliberately invite disrepute: The Paperboy. Director Lee Daniels and novelist Pete Dexter share screenwriting credit on the adaptation, the biggest surprise of which is how the script makes aspects of Dexter's late '60s Deep South mystery story trashier and wilder than what's in the book. Another instance of a source author and a director collaborating on a script and delivering a lot of fun is the black comedy Bernie. Working from a Texas Monthly article about the true-life murder of an old lady by her only friend and companion, Skip Hollandsworth and Richard Linklater wrung wonderfully mordant scenes from a case history.

But among the liveliest feats is David O. Russell's Silver Linings Playbook, which he adapted from Matthew Quick's novel. As if in a one-on-one basketball matchup, Russell shoots from all angles, a layup here, a hook shot there, a long three-pointer, then a dunk.

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