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There have been a few presentations now in which a live stage performance was simulated by what was described as a hologram. The most recent example of this was the Michael Jackson "appearance".

How are these done? The classic hologram I am familiar with uses only one wavelength of laser light and constructs an interference pattern on a photographic plate, where it is recorded. When the same light source illuminates the developed plate, the interference pattern effectively reconstitutes the original light paths to reproduce the effect of looking through a window (the plate) to view the original object as if it was illuminated in monochromatic light (that of the laser).

The stage presentations obviously differ in that they are in full colour, and they are moving in real time... not to mention the overall physical size.

So, what's different about the way these presentations are prepared and executed that allows them to render in such a life-size and life-like manner? Are they truly holograms? Do they employ the same principles of physics as a "classic" hologram? Are they actually something entirely different and only incorrectly labelled as holograms?

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Are they actually something entirely different and only incorrectly labelled as holograms?

Yes, they're a variation of a century-old trick named Pepper's ghost. A special "invisible" foil is spanning the stage, and an image is projected onto it via mirrors like this:

enter image description here

The foil used here is the main invention that made this type of holograms popular. Source: a CNN piece on the firm HologramUSA. Their partners later claimed that the "hologram" used in that Michael Jackson appearance was a ripoff of their patented technology. They lost a law suit, but the technical setup was similar

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    $\begingroup$ +1 I have corrected my answer . $\endgroup$ – anna v Apr 19 '18 at 10:11
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Here is the video of the performance.

So, what's different about the way these presentations are prepared and executed that allows them to render in such a life-size and life-like manner? Are they truly holograms? Do they employ the same principles of physics as a "classic" hologram? Are they actually something entirely different and only incorrectly labelled as holograms?

First of all remember that color perception is synthesized in our eyes/brain and we need just three colors of the frequency rainbow (though Land of polaroid technology had used just two to create color perception in photos) to create the full rainbow in our perception. Certainly using three lasers is not such a great technological leap.

Considering that a legal battle has started about the technology used, the difficulty is not in the physics, but in the sophisticated photo shop type techniques to animate and control holographic images, i.e. make a movie out of sequential holograms and be realistic enough.

Update:

I corrected the broken link , and one can see in the description that the word "hologram" used does not have the physics definition as they are using normal lights, and actors, not lasers. Using three lasers is still science fiction.

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