Joe Kosinski says de-aging Jeff Bridges was "difficult" on 'Tron: Legacy'.

The Oscar winning actor appears as a younger version of himself in the film - and director Joe says shaving years off the 60 year old's face to play villain Clu was "pushing the envelope of what's possible."

Joe said: "The first 'Tron' set the bar so high in terms of technology that we knew we really had to try hard with this film, and I think with the character of Clu we are definitely pushing the envelope of what's possible."

Jeff's features were digitally enhanced so he looked like his 30-year-old self using a high-tech process called facial capture.

He also stars in the film in his natural form as Kevin Flynn, whom he played in the original 1982 movie.

Joe said: "There is nothing more difficult than trying to achieve a photo-realistic human being.

"The way we tried to achieve it was to capture as much of Jeff's performance as possible digitally, and you see real glimpses of him in Clu.

He added to The Daily Telegraph newspaper: "Those glimpses, I think, are really exciting and show a great potential for the future of film technology. This is such an interesting place to be."