Director David Cronenberg walked away with the audience prize at this year's Toronto Film Festival for his latest work, Eastern Promises, the story of ruthless Russian gangster Nikolai (Viggo Mortensen) whose path crosses with midwife Anna (Naomi Watts) setting into motion a chain of harrowing and bloody events.

The film reunites Cronenberg with actor Mortensen, who also starred in Cronenberg's 2005 film, A History of Violence. And Cronenberg says the most crucial part of any movie is getting the right people.

"You have to have a good sense of casting," he told CNN. "If you miscast the movie you are finished. No matter how much you think you're a Svengali who can take a bad actor and make him great, you really can't. It's much better to start with a great actor, cast well. Then you start at a much higher level."

Cronenberg praised Mortensen's "wonderfully intelligent, subtle acting" and told CNN of the pleasure in working with someone who puts so much preparation into his roles. "It's fantastic," he said. "You have another collaborator from an unexpected source."

For his part, Mortensen jumped at the chance to work with Cronenberg again, and is full of reciprocal praise for him. "I do think he is one of the true masters as far as directors go," he told CNN.

Cronenberg is also one of the world's most controversial directors. With films like Crash, Naked Lunch and A History of Violence to his name, he has mined the darkest corners of the human psyche. His explorations of sex, violence and the human body have brought him acclaim and fortune, but he's also received criticism from some quarters.

Cronenberg is clear that his films aren't for everyone. "Some people are just interested in light entertainment; some people are interested in movies as philosophy," he told CNN. "Those are my kind of people."

Some find his graphic depictions of violence distressing. "It is an element of exploration in the films I take seriously," Cronenberg acknowledges. "It's very easy to use violence in a film that is just light entertainment and frankly I don't have a problem with that; it's just not my approach."

This time around, Cronenberg is pushing the boundaries once more, with a benchmark fight scene that's set to become a classic. The four-minute bath house sequence required meticulous planning, as Cronenberg had just two days to shoot it.

"A lot of preparation went into it," he said. "The bath house is a set and every little element of that was discussed by me and my production designer, Carol Spier: the tiles, the shape of the room, the small rooms opening into hallways that open into bigger rooms."

And Cronenberg knew that he had to get everything just right.

"The lighting, the choreography, the sound effects and the editing, all of these things take a lot of work," he said. "If one element falls down, then the whole scene is ruined. If the editing is great but the lighting is no good, or if the performances are great but the choreography is boring, you don't have a scene. Everything has to work."

Filming the fight scene proved gruelling for the actors. Viggo Mortensen was relieved that the bath house shoot was completed on time. "I was pretty bruised up halfway into the first day and the sooner it was over, the better," he said.

His co-star, actor Vincent Cassel, was amazed by the results. "It's something I have never seen on screen," he told CNN. "It's really original, it's very daring, it's crazy and it looks beautiful."

While Cronenberg's detractors will cite the bath house scene as another example of the director's fondness for violence, Cronenberg believes that movies have to find the balance between being graphic and gratuitous. "You've got to do it for real to have the resonance that it would have if it came into your life," he said. "That's where the level of reality in my movies, particularly in Eastern Promises, is very solid, something that people are reacting to in a very intense way."

Certainly, Cronenberg's cameras don't shy away from the bloodier moments. "Scenes that have a lot of quick cutting and you don't see what's going on, like the Bourne movies, you don't really want to disturb your audience too much. You don't want the thrill ride to be over," he said.

"But in my movie I'm asking you to take it fairly seriously and because I do, some people find that off-putting. They would rather not deal with that, and in that case my movies are not for them."

His actors are keen to underline this distinction. Vincent Cassel said, "He does use violence as a tool and he knows how to deal with it on the screen. It's never to have fun with it. He wants you to feel what it means to be wounded."

Mortensen agrees. "He is one of the most responsible directors in terms of the way he handles violence, because you see it honestly," he told CNN. "It is disturbing, and it should be. You do something when you're committing violence: you are destroying a human body."