BEFORE BOB FOSSE’S hellzapoppin’ movie and the heelzatappin’ Broadway production of Cabaret, there was I Am A Camera, a modest monochrome 1955 film of the 1940s play of the 1930s novel Goodbye to Berlin, by Christopher Isherwood.

In it, the struggling young writer-narrator complains that the unhappy characters in his first novel have no faces. But of course the actor Laurence Harvey has just given a face to the author, “Herr Issyvoo”, who is faceless in the novel that will become the play that will become the film of the novel that will become a bestseller . . .

There are readers and there are viewers: readers have read or will read the novel before watching the film; viewers will buy the novel after they have seen the film. It is an important difference. Readers will watch the film with literal (not to say literary) expectations; viewers will read only with filmic preconceptions about the stars and director. Is this film right for Tom Cruise? (The author Anne Rice originally thought him wrongly cast as the vampire Lestat in the film of Interview with the Vampire; viewers rated him box office gold).

Who can now read Gone With the Wind without a mental picture of Clark Gable and Vivien Leigh; A Streetcar Named Desire without seeing Marlon Brando as Stanley Kowalski; War and Peace without a vision of Audrey Hepburn as Natasha; or Breakfast at Tiffany’s without seeing her as Holly Golightly. And for how long will the face of Colin Firth be identified as Mr Darcy in Pride and Prejudice? Actors define characters, just as directors and cinemaphotographers can impose a “look” on the film of the novel — E. M. Forster and Henry James both owe a lot in terms of continuing sales to Merchant Ivory.

How important is the novel, really? It is culturally acceptable to watch a movie of the novel; less so to read a novelisation of a movie. K. W. Jeter has written a series of books based on the Bladerunner movie, itself adapted from Do Androids Dream of Electric Sheep?, a novella, by Philip K. Dick who, in Hollywood terms, did not write enough. Only a short story? Where's the percentage in that?

The novelisation of the novel — a whole new postmodernist concept. I am waiting for the Jane Austen novelisation, Pride and Extreme Prejudice: Dirty Harry meets Elizabeth Bennet.

A dead author cannot complain when a director takes cinematic licence with a novel. P. L. Travers unsuccessfully tried to wrest control of her Mary Poppins character from Walt Disney; and Patricia Highsmith had just cause to complain about the comeuppance given to her adored, amoral character, Tom Ripley, when, in the first adaptation, Purple Noon, starring Alain Delon, the police closed in to arrest him for his murderous fraud. Ripley gets away with it in the book to resurface in a series of novels — he was too good a character to lose. At least the film was true to Highsmith’s character. In 1955, “Herr Issyvoo” could only subliminally, subtly be presented as homosexual (Laurence Harvey is allowed to say only that he is “a confirmed bachelor”) whereas for Isherwood, “Berlin meant boys”. Michael York, who played Brian Roberts (Isherwood's alter ego in Cabaret) is a gay man who has an affair with Sally Bowles, the nightclub chanteuse played by Liza Minelli, who gives him up as wholly gay rather than apparently bisexual. Isherwood approved of York both as a blond beauty and as an actor prepared to play the role as the novelist preferred.

“Herr Issyvoo” or “Brian Roberts” is simply a foil for the spectacularly dizzy Sally Bowles, played in I Am A Camera, by Julie Harris (looking and sounding startlingly like Felicity Kendal). Cabaret, directed and choreographed by Fosse, was surely conceived as a star vehicle for Minnelli, whose Sally is now definitive. Her performances at the Kit-Kat Club would now make any low dive the hottest ticket in town. But don’t dismiss Harris — don't tell me Truman Capote did not take some cues from Sally for Holly Golightly, and from Herr Issyvoo for the unnamed narrator in Breakfast at Tiffany’s, published in 1958, three years after I Am a Camera. Sometimes a novel eats a movie that is eaten by a novel . . .

Small pages, big screen

CABARET Goodbye to Berlin by Christopher Isherwood, play by John van Druten

THE GRIFTERS novel by Jim Thompson

THE TALENTED MR RIPLEY novel by Patricia Highsmith

BLADERUNNER short story, Do Androids Dream of Electric Sheep?, by Philip K. Dick

DEATH IN VENICE novella by Thomas Mann

THE WIZARD OF OZ novel by Frank L. Baum

APOCALYPSE NOW Heart of Darkness, by Joseph Conrad

SATURDAY NIGHT FEVER magazine article by Nik Cohn

THE GODFATHER novel by Mario Puzo

ON THE WATERFRONT investigative journalism by Malcolm Johnson and Budd Schulberg

Explore Books

• Book Extracts

• Book Reviews

• Books Group

• Audio Books

Times Recommends

• The 100 Best Books of the Decade
• The Times picks the 50 best paperbacks of 2009
• The conversation: James Ellroy