Elvis on 'Idol:' How It Was Done

Those who say Elvis Presley is dead must have missed "American Idol" this week.

(ABC)

The late king of rock 'n' roll performed a hip-shaking duet with Celine Dion on Wednesday's show. The images of him seemed so real, many people were left wondering how "Idol" was able to bring him back from the dead.

Fans can thank technology. Last week, Dion spent hours on the stage singing her part of the song several times without an audience or anyone next to her, looking to her side on cue.

Then she did the routine again with a Presley body double who lip-synced Presley's song and matched his moves from his 1968 performance.

Finally, all three elements -- Dion by herself, Dion with the body double and the original Presley performance -- were combined through editing and a technique called rotoscoping, which traced Presley from the original footage by cutting him out.

"Rotoscoping allows you to take one image from a pre-existing piece of video and puts him a whole new environment -- completely new use of that same piece of video," Disney digital media designer Joe Husung said.

Similar technology has been used before. It brought Natalie Cole and her late father, Nat King Cole, together to perform "Unforgettable," and allowed Forrest Gump to talk to former President Nixon.

A new British show puts the technology to use every day in "Duet Impossible," in which stars perform with their late idols. If the concept crosses the pond, American audiences may soon see late legends like James Brown and Sinatra rocking the stage again.