Elvis performed with Celine Dion thanks to rotoscoping, a body double

Was last week’s Idol Gives Back duet between Celine Dion and long-dead Elvis Presley a hologram? A body double? CGI? Actually, it was a combination of technologies, although not, as some people speculated, a hologram.

First, “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,” Good Morning America reports.

She then performed “with a Presley body double who lip-synced Presley’s song and matched his moves from his 1968 performance.” Those were digitally merged with Elvis’ performance “through editing and a technique called rotoscoping, which traced Presley from the original footage by cutting him out.”

Disney’s Joe Husung tells GMA, “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.”