The fact that the Fifty Shades trilogy became such a phenomenal success is something of a miracle in itself – who could have imagined that 70 million people would pay top whack (ahem) for sadomasochistic erotica? And the miracles continue, with growing talk that the film adaptation mightn't be half-bad.
EL James's novels are infamously dreadful as literature, with clunky characterisation, ridiculous plotting and laughable dialogue. But with decent actors Charlie Hunnam and Dakota Johnson playing the lead roles, and respected director Sam Taylor-Wood at the helm, there's talk abroad that Fifty Shades could be worth watching; one critic predicted that the movie would be "serious, art-house and gritty".
It's happened before, of course, where a production has transmuted its base origins into cinematic gold. And the reverse is true – probably more often, in fact – with great novels rendered dull and inert by their transition to the screen.
Sean Rocks, the presenter of arts show Arena on RTÉ Radio 1 which has regular book and film slots is well-qualified to look at this issue from the perspective of both mediums.
He says: "I think the task of transferring book to film becomes problematic when the filmmaker tries to be totally faithful to the novel. Sometimes what reads brilliantly can't be transferred directly to the screen; the filmmaker needs to find a visual conceit to match the literary one, or simply accept that a certain scene in the book may not work in the movie.
"There's also an issue round having read the book first. A film will simply never match what you've done in your own imagination, no matter how extraordinary the adaptation or how brilliant the filmmaker."
On the flipside, poor novels can often make for cracking films.
Critic Laura Miller, of culture website Salon, suggests that filmmakers may feel more free and agile when working with less revered source material. She also reckons that "we're more willing to forgive a film for the faults that damn a book".
Here we've picked five of each type: bad to good, and back again.
Bad books to good movies
* The Godfather
The original novel actually wasn't too bad, but this must make the cut purely because The Godfather (left) is, many agree, the greatest movie ever made, perhaps matched only by its sequel. Both films more-or-less tell the one extended story, culled from Mario Puzo's potboiler.
* The Twilight series
Fifty Shades, of course, was inspired by Stephenie Meyer's vampire romance, and Twilight was equally dissed by critics. But the films, at least up until the misjudged Breaking Dawn two-parter, were excellent: poignant, wistful meditations on life, love and the pains and thrills of growing up.
* There Will be Blood
The film that won Daniel Day-Lewis (right) the second of three Oscars was based on a book called Oil! by one Upton Sinclair. His novel is never going to trouble those "Greatest Ever" listings, but Paul Thomas Anderson reworked it as a grandiose, almost Homeric epic about America's history and self-mythology.
* A History of Violence
The graphic novel on which David Cronenberg based his film, like many comic books, was brutal, shocking (not in a good way), ridiculous and quite childish. The movie (left), on the other hand, was an absolutely riveting exploration of conscience, identity and great philosophical questions about change and redemption. Plus, the action scenes really rocked.
* The Bridges of Madison County
Robert James Waller's 1992 romance, much like EL James's work, sold tens of millions of copies, but was excoriated by anyone with a critical faculty in their head. Under the astute direction of Clint Eastwood, though, the original story became thoughtful and very moving. The film even made Clint into a heartthrob (sort of).
Good books to bad movies
* The Great Gatsby
The defining characteristic of F Scott Fitzgerald's iconic novel, for most readers, is its subtlety. Its power is all the greater for being so understated. Too often, though, moviemakers misread the work as a brash, shining encapsulation of the Jazz Age. So there have been several film takes on The Great Gatsby, all of them poor, and none worse than last year's from Baz Luhrmann.
* The Bonfire Of The Vanities
Tom Wolfe's late 1980s satire of corporate greed and New York high-society was a rollicking read, full of smart observations and laugh-out-loud scenes. Brian de Palma's adaptation was as enjoyable as a needle in the ear.
One of the greatest novels of the 20th Century, Vladimir Nabokov's classic was artistically courageous and beautifully expressed. Stanley Kubrick tried an adaptation in the 1960s which was okay, but only that. And the 1997 version starring Jeremy Irons was awful, bordering on laughable.
* The Scarlet Letter
Demi Moore isn't without some qualities as an actress, but The Scarlet Letter wasn't the right vehicle to showcase them. The novel, by Nathaniel Hawthorne, is a gloomy tale of guilt and sin in colonial times. The filmmakers took total liberties with the original, and even gave it a daft Hollywood ending.
* The Hitchhikers' Guide to the Galaxy
They did the seemingly impossible: made Douglas Adams boring. His spoof sci-fi novels were fast, funny and crazy, sizzling with invention. The film version was as dull as the dressing-gown Martin Freeman wears for much of it.