CANNES: The business of picking winners may be the Cannes Film Festival jury's raison d'etre, but it leaves Woody Allen so cold that he has always refused to be up for a prize at the annual extravaganza.

The veteran American actor and director opens the show for the third time on Wednesday with 'Cafe Society', but once again his film will not be in the main competition, whose judges are this year led by Australian director George Miller.

"For any group to come together and judge the work of other people is something I would never do," Allen told a news conference on Wednesday.

"It...is something I do not believe in. So I do not want to participate in it."

Miller and his team -- which includes American actress Kirsten Dunst, Danish actor Mads Mikkelsen, French singer/actress Vanessa Paradis and last year's Palme d'Or winner Laszlo Nemes of Hungary -- will however judge 21 films.

"You could argue how do you measure these films, but that's definitely balanced by the simple joy of being here watching films that are new, watching them with consideration and then having a conversation," Miller said.

"We're all very humble with the task. The biggest obstacle is we are bringing different qualities, we have a different approach - some film makers, directors, actors, so the task is to try to forget that and become an audience again," said Mikkelsen.

For Dunst, the competition is simply vital for cinema in general.

"Without film festivals like this we wouldn't see movies, and they would not become famous like (Nemes's) 'Son of Saul'," she said.

"We need these festivals to promote film makers... Without that we would just be in big blockbusters all the time."