'Harry Potter' actor Timothy Spall depicts painter J.M.W. Turner in Mike Leigh's 'Mr. Turner' at the Toronto Film Festival.

Mr. Turner, the portrait of the great British painter J.M.W. Turner which won Timothy Spall the Best Actor prize at Cannes in May, is not a conventional biopic. Director Mike Leigh, who as is his custom built the movie's script out of improvisations with his cast, is resolutely — one might fairly say stubbornly — resistant to the conventions of filmed biography, resisting easy (and often any) explanations for what drove him. Spall's magnificently gruff performance, full of guttural grunts and groans, is invested more in process — he learned to paint for the role, half-seriously boasting he has become as good a painter as "Turner when he was nine" — than in psychology. His Turner, who decorates his canvases with globs of spit and carves lines into the paint with his fingernails, is as much animal as man, resembling nothing so much as the hog's head his father brings home along with a fresh batch of pigment in Mr. Turner's early minutes.

Mr. Turner is, of course, populated with a wealth of historical figures: painters, patrons, critics, even Queen Victoria and Prince Albert, who pronounced one of Turner's less representational later works an unglaüblich disaster. But the most powerful actor in the movie, which covers, roughly speaking, the last few decades before Turner's death in 1851, is technology. It's a pleasing curiosity when science writer and "natural philosopher" Mary Somerville calls on Turner to show him the wonders of the optical prism, or when Turner marvels at a decades-old gunship being towed into port by a modern steam tug to be sold for scrap — the subject of his painting, "The Fighting Temeraire tugged to her last berth to be broken up, 1838." But when the daguerréotype, invented the following year, begins to make its influence felt, Turner prophesies that painters will soon go about with "boxes" instead of brushes: a clear, if not overly heavy-handed, reference to the recently imposed transition from celluloid to digital cinema.

In other words, Mr. Turner is not a biography of Turner so much as it is a partial history of his art form. Noted figures float through, but as living shorthand: the painter Benjamin Haydon (Martin Savage) begs Turner for money to pay off his debts and screams at a gaggle of sneering peers, "Stretch me no longer on this rough world!" a phrase that in actuality he would reserve for his suicide note; the influential art critic John Ruskin (Joshua Maguire) appears as a preening dandy with a speech impediment (Leigh is not known to be fond of critics). Given equal prominence is the first camera Turner encounters. ("Not 'camerah'?" he asks, preferring the Latin.) Like the gun in Akira Kurosawa's Ran, its appearance changes the world for good; when Turner gazes upon the paintings of his colleagues, he sees a proliferation flat, unimaginative realism, trying to beat the apparatus at its own game. Instead, Turner heads in the opposite direction, rendering locomotives as blurs of black steel ripping through the landscape.

Although it's only a piece of his artistic career, his progression throughout the period covered by Mr. Turner is profound, which may be why he rejected offers to buy individual canvasses in favor of donating the lot to "the British nation," a bequest which sadly is now honored only in the breach. Taken as a whole, they tell a larger story, not only of an artist's development but of the world's, a movement from the subjectivity of painting to the objective delineations of photography. The entirely purposeful irony is that Mr. Turner is also Leigh's first digital film, not only shot on the new medium but taking advantage of its capability for special effects — removing modern houses from a period-dressed frame, plopping a rowboat into a digitally created Thames, and so forth. As shot by master cinematographer Dick Pope, it's alive with the rich colors and mottled textures familiar from Turner's paintings — a pan down jagged seaside rocks is initially indistinguishable from paint on canvas — proof that even as we move into the future, we need not lose sight of the past.