Joaquin Phoenix thinks ''people are gonna be mad'' that 'Joker' doesn't ''follow anything'' from the original comic books.

The 44-year-old actor fears that the upcoming movie based on the origin of the DC Comics villain may not live up to fans expectations as he and director Todd Phillips chose to stray from the original DC material and focus on the ''story of becoming Joker''.

Phoenix said: ''We didn't follow anything from the comic books, which people are gonna be mad about. We just wrote our own version of where a guy like Joker might come from.

''That's what was interesting to me. We're not even doing Joker, but the story of becoming Joker. It's about this man. ''

The 'Gladiator' actor added that he thought the project sounded ''super ambitious'' when he first discussed it with Phillips.

He told Empire magazine: ''I thought it was crazy-ambitious. Todd said to me 'I have this idea, I wanna tell the origin story of the Joker. I said 'Wow okay'''.

The 'War Dogs' filmmaker went on to explain that he didn't use ''one green-screen'' in the film as he feels the ''energy'' from an actor is different if they're filming in real locations rather than a studio.

Philips said: ''In the most reductive way it's the New York of 1981 that I remember. It's a broken-down city, and the people in it are broken down.

''The energy you get from the actor is different on 179th street and Jermone Avenue in the Bronx than if we did that green-screen, which, by the way, I don't even know how to do shit like that. There's not one green screen in this movie. ''