When Dr Dre and Snoop Dogg co-headlined California's Coachella festival on Sunday evening, they were joined onstage by some of hip-hop's finest, including Eminem, 50 Cent, Wiz Khalifa and Warren G. But the biggest cheer of the night was reserved for rapper Tupac Shakur, who arrived mid-set to perform two tracks, "Hail Mary" and "2 of Amerikaz Most Wanted". Just one detail to note: Tupac died in 1996 at the age of 25, of course, having been shot four times while out driving in Las Vegas.
Resurrected by way of a hi-tech 3D hologram that had taken months to develop, Tupac's return to the stage was the talk of the festival, with audience members tweeting their disbelief at how life-like the hologram was.
"I think I might have cried when I saw Tupac," wrote popstar Katy Perry, while Questlove of The Roots said, "That Pac hologram haunted me in my sleep". Rihanna simply tweeted "#TupacBACK #unbelievable". The hologram was developed by AV Concepts, using technology licensed from Musion, a British company that developed the technique and which retain a global patent on it.
Using updated Pepper's Ghost technology (a Victorian-era illusionary method), it is a high definition 3D holographic video projection system allowing 3D life-size moving holograms to appear within a live stage setting.
The system works by placing thin metallised film across the front of the stage at an angle of 45 degrees towards the audience. Recessed below the screen is a bright image supplied by an LED screen or powerful projector; when viewed from the audience's perspective, the reflected images appear to be onstage.
"It's an ongoing process but the technology just gets better and better," says James Rock, Director of Musion. "When people cotton on to what can be done, I'm certain we'll see a lot more instances of deceased performers being brought back to life. Obviously there are issues with the estate and licensing the content from them but the technology is there."
It is by no means the first time holograms have been used in live music. Just last November, the singer Mariah Carey performed five simultaneous concerts in five countries as a 3D projection. Holograms of The Black Eyed Peas performed at the NRJ Music Awards earlier last year.
The technology can also be used for musical performances by non-human acts. Musion created the Gorillaz holograms that have performed the majority of the virtual band's live shows since 2005, and the animated Japanese pop star, Hatsune Miku, has also been brought to life to perform concerts with the same method.
Of course, it is markedly eerier when such technology is used to bring artists such as Tupac back from the grave. For his 50th birthday party, Simon Cowell hired Musion to create a hologram of his (deceased) hero, Frank Sinatra, singing "Pennies From Heaven" that performed for his 400 guests. And in 2007, American Idol viewers were shocked to witness Celine Dion duet with Elvis Presley on his hit "If I Can Dream" (although this was done using a process called rotoscoping, which allows you to take one image from a pre-existing piece of video and put it in a whole new environment, as opposed to using a hologram projection).
It seems that anything is possible: The Beatles reunion tour featuring all four members; Freddie Mercury fronting Queen once again.
Someone should certainly inform the London Olympic organisers, who unwittingly provided much hilarity last week after it was reported they had approached The Who's manager to ask if Keith Moon would be available to perform with the other members at the opening ceremony.
Moon might well have died in 1978, but with all this amazing new technology, perhaps The Who's original line-up could still entertain the crowd after all.