There’s been a lot of buzz going around about Tupac’s Resurrection at Coachella. The word hologram is getting thrown about a lot. The image is eerily realistic, and it sure is a fun stage gimmick, but it’s not a hologram and it’s also not all that new.
The technique used to bring Tupac back to life is known as “Musion Eyeliner”. It’s a variant on an old stage trick called Pepper’s Ghost. If you’ve ever been on the Twilight Zone Tower of Terror ride at Disney Hollywood Studios1, you’ve seen Pepper’s Ghost in action.
Holography vs. Fancy Projection Techniques
Primarily, Holography (with the product of Holography being a Hologram) is a recording mechanism. It’s extremely similar to the idea of Light Field Photography the likes of which are being used in the Lytro camera. The difference is that Light Field Photography uses optics and lensing to capture information at a certain focal length.
Our ability to see objects is a result of the fact that everything in the physical world has a tangible effect on light that strikes it; reflecting, refracting, and scattering light. The way the light is warped by objects in the physical world is what gives these objects their optical properties; colors, hues, shades, etc. Photography uses a lens to focus on an area in and it captures what the light is doing in that area; if there are objects present, the objects get recorded because the light gets captured on to a recording medium (film, digital sensor, etc). But a photograph only captures the light moving in one direction.
Holography captures an entire “field” of light. When a hologram is recorded, it doesn’t just record what the light in that area is doing in one direction, but all directions. This is what gives the impression of 3D imagery recorded on to a 2D medium. Holography also captures the light scatter directly on to the medium without optical lensing. They are typically created by scattering light from a laser.
The Tupac performance is clearly not a recording of a past performance, so what is it? As I mentioned before, it uses a variation of Pepper’s Ghost called Musion Eyeliner. People have been using Musion Eyeliner for years now; in fact, it’s how the Gorillaz perform live since they are a band made entirely of cartoon characters. A very thin, clear film is placed on the stage and then angled towards the viewing area. This film has a transparent metallic coating to give it optical properties allowing for reflection and scattering of the light in a way the lets it achieve its effect. A projector sends the imagery downwards towards an LED backlit screen sitting underneath the film, which is reflected by the film in a way that creates the 3D “image” that the audience sees. The image is in fact a 2D image on a screen, and since the source image is not a capture of a light field in any way but just a carefully constructed 2D image it is not by any definition proper holography:
Image from event works
It’s definitely an impressive feat. And I’m not trying to cheapen how cool the effect is and how much it added to the performance. But as a man of science, it is my job to poo-poo all over cool shit when someone is wrong. Until next time.
And if you have not, then there’s something seriously wrong with you, because it’s basically the greatest theme park experience ever created. Not just the ride itself, but the combination of the actors, the setting, the backstory, and totally it immerses the riders. It simply can’t be topped.↩