By Roxanne Palmer

The resurrection of rapper Tupac Shakur wowed audiences at the Coachella music festival. But the illusion isn't a hologram, as some have reported -- it's actually a 2-dimensional video cleverly projected using technology based on an old theater trick.

Tempe, Ariz.-based AV Concepts orchestrated Tupac's performance using London-based Musion Systems Ltd.'s Musion Eyeliner setup that was able to project an animated version of Tupac -- created by visual production house Digital Domain -- onto a screen that appeared invisible to the audience.

By Roxanne Palmer

The Musion Eyeliner system is based on Pepper's ghost, a theater technique for producing illusions that has been used for centuries in plays and magic tricks.

In the stage version of the illusion, an actor is hidden in a recessed area below the stage and faces a mirror. The audience sees the actor's ghostly image reflected in a sheet of glass suspended above the stage, and lighting can be used to make him or her appear or disappear.