he star TV talk-show hostess Oprah Winfrey has been involved over the years in three significant movies based on celebrated novels by black authors. In 1985, she appeared as a natural rebel alongside Whoopi Goldberg in Steven Spielberg's skilful, soft-centred adaptation of Alice Walker's The Color Purple about the oppression of black women in the Deep South, the need for sisterhood and the romance of Africa.

In 1998, she produced and starred in Jonathan Demme's film of Toni Morrison's Beloved. In this ambitious failure, Winfrey played the runaway slave who kills her baby rather than see her recaptured by white pursuers and, a decade after the Civil War, is haunted by the child's ghost. Now she is the ­co-producer of Lee Daniels's Precious, adapted by Geoffrey Fletcher from Push, the bestselling 1996 novel by Ramona Lofton, the writer and performance poet who styles herself "Sapphire".

Made on a much smaller budget, Precious is a simpler, tougher work than the two preceding films and altogether more effective. The setting is Harlem in 1987, the central character the obese 16-year-old black girl Claireece Jones, known as "Precious", unforgettably played in her first professional role by the vast, imposing Gabourey Sidibe, daughter of a New York gospel singer and a Senegalese father. Precious is illiterate, aggressive, constantly tormented by fellow high-school pupils and abused, both physically and verbally by her alcoholic mother and father. She has a daughter with Down's syndrome by her father, who constantly rapes her with the mother's connivance and is pregnant again by him. Later, it's revealed that the father has died of Aids.

You might well ask who is in the market for such a film and one thinks of Eliot's smug statement: "Humankind cannot bear much reality" and those newsreaders who preface horrendous reports from Haiti with the warning: "There are scenes some viewers may find disturbing." But over the years there have been a number of highly acclaimed pictures of this kind. Just after the Second World War, for instance, there was a widely shown Danish picture called Ditte, Child of Man, about the unremittingly miserable life of an illegitimate, working-class girl with a drunken mother, a brutal stepfather who was raised in poverty, seduced and abandoned.