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In the new sci-fi action thriller Gemini Man, Will Smith battles with a younger clone of himself which filmmakers say represents Hollywood’s biggest leap forward yet into futuristic computer generated imagery.

The fresh-faced younger Smith in Paramount’s film is entirely built with special effects, right down to his eerily realistic pores, sinews and blood vessels.

It is unlike several movies that employed “de-aging” techniques to airbrush wrinkles on grizzled stars.

“In the past we would have had Will Smith’s son play it ― he would have been put in different hair and makeup, and we’d have called him a ‘clone’,” director Ang Lee told reporters in Los Angeles.

“But it doesn’t look good in this media,” he added, referring to the film’s state-of-the-art 3D shots, which include several close-up, visceral fight scenes.

For more than two decades, Gemini Man has been trapped in development, bouncing between studios, directors and stars as Hollywood waited for technology to catch up with the movie’s plot.

The trailer shows a young clone assassin sent by a shadowy organisation to kill his older self.

Out in October, the techniques used in Gemini Man are similar to those used in Disney’s recent “live action” version of The Lion King.

Bill Westenhofer, effects supervisor said that creating a realistic-looking human face has been an unachievable goal of visual effects for a long time.

“Every single one of us are experts… over millions of years, the face is how we look at someone and tell that they’re lying to you or that there’s an illness,” he explained.

“The subtleties of what tells you that are subconscious. So for us to go in and try to recreate that digitally is really hard.”

Smith and stunt doubles acted out the younger character’s part in motion-capture suits before the visual effects were applied on top of their movements.

Old photographs and footage of Smith from his twenties, the age of his character’s clone “Junior” in the film, including Bad Boys and Independence Day were looked through by filmmakers.

They studied the morphology of aging, and looked at human anatomy from how facial muscles interact right down to the microscopic level of skin pores and melanin pigment.

Producer Jerry Bruckheimer, who has been on board with the project for over a decade, said the “revolutionary” leap in technology and detail was the equivalent of “going from black and white into colour.”