Holograms, what they are and how the moving ones of Michael Jackson and Whitney Huston work

The movies of science fiction have been suggesting to us for decades that we will one day communicate via our digital reproductions, such as the Princess Leia in Star Wars.
Perhaps, however, few expected that we could see Michael Jackson, Whitney Houston or Tupac perform on a stage years after their departure. Today it happens with the holograms! Are we sure we know what it is? And are they all made the same way? Let’s dispel some myths together.

What are holograms?

The holograms are the result three dimensional of the projection of an object, obtained through the interference of two laser beams.

They were invented in the 40s of the twentieth century by Dennis GaborHungarian scientist who conquered the Nobel prize for this invention in 1971. It was only in the 1960s that we began to make them holograms with light: they used to be made with electrons since lasers hadn’t been invented yet. Holograms are therefore images that appear in 3D but which, in reality, are made on a surface in 2D. Particularly:

  • are equipped with motion parallax – that is: when you move your gaze, the objects in the image that are in the foreground seem to move faster than those in the background. In this way we get different images depending on where we stand to watch them;
  • they return the stereoscopic visionor the fact that we can see two different images, one for each eye, which together give the depth perception.

How does a hologram work?

Let’s briefly see how holograms work, step-by-step.

A starting point

Before we see how a hologram works, we need to understand how a photograph works.
We have the subject of the photo and the light (of the Sun or camera flash) bounces off it. That same light that bounced off the image passes through the lenses of the camera and then goes up to the CCD of digital cameras or on the photographic plate in analog ones. On the slab yes impresses the light and we get the picture.

Double laser beam

In the case of the hologram, the concept is similar, but a little more complicated.
Simplifying: we start from a laser whose ray comes split in two through a mirrored surface partially silvered. Both sides pass through lenses to make the beams expand. So you will have:

  1. a first part which is called reference radiuswhich arrives (after encountering reflective surfaces and lenses) on a sort of photographic plate which in this case is called holographic film. Being an unmodified laser beam, the radius of reference it is said coherent – that is, all light waves are in phase or in unison;
  2. a second part of laser beam, the object radiuswhich is bounced off the object and then bounced off holographic film. The radius of the object, unlike the first, not it is a ray coherent.

This way you get one interference pattern in which the two parts of the beam endowed with different characteristics are combined and this is what allows to obtain the information necessary for the 3D rendering. On the final film, in fact, line lines are produced in this way fringes of interference which are used to return the three-dimensionality.

hologram laser pattern

From interference pattern to hologram

So we have one interference patternbut it’s not exactly thatsharp 3D image which we would expect. To carry out this last step it is necessary to resume the original laser beam and aim it at the final holographic film. This way it is possible reverse the whole process, recreating the ray that originally bounced off the object. The radius we will obtain will be identical to the one we called object radius. And it is for this reason that when we look at the hologram of an object it seems that it is actually there: yes recreate the light which it originally has hit the object.
Here is a hologram created, but in this case it is stationary, fixed.

schematic hologram

Moving holograms

How do you create moving holograms? To answer this question, let’s take as reference some of the most famous cases in this field.

Whitney Houston’s hologram

Unfortunately at the moment the creation of a moving hologram it really turns out hard due to structural limitations.
To be honest the creators of the Tour “An Evening With Whitney”, which from 2021 brings on stage a hologram of the amazing Whitney Huston, claim to be using a technology of this type (laser) and able to reproduce the three-dimensional image of Whitney.

There singerpassed away in 2012, it moves in hologram version, sing and dance on stage with several different outfits. The one thing she can’t seem to do is climb the stairs.
There surrender It’s realisticbut the Base Hologram Company – which is following the project – did not disclose the details of the functioning of the technology.
What is certain is that for reproduce the image of the singer has been used a lot CGI (Computer Generated Imagery), especially for the reconstruction of the face. A great job of impersonation was also carried out by aactress – with a physicality similar to that of the singer – who faithfully copied her movements and her image was then reproduced in computer graphics.

Pepper’s Ghost: the “fake” holograms of Michael Jackson and Tupac

Some argue that another type of trick was used for the Whitney Huston hologram tour, also present in the performances of the reproduction of Michael Jackson to the Billboard Music Awards of the 2014 and from that of Tupac Shakur to the Coachella in the 2012.

This is the effect known as Pepper’s Ghost (or Pepper’s ghost), a illusory technique used in theaters since sixteenth century. At that time, a actor place under the stagewhose image was reflected on a transparent plate on the stage.
Today the technique is very similar and involves the use of a projector which projects the video with the artist performances – digitally reconstructed – on one reflective screen generally placed on the floor. From this screen the light is refracted on a transparent surface here I’m on stage inclined by 45th.
In this way the audience receives a two-dimensional image of the artist without the transparent screen being visible. Not therefore it is about a true is exactly hologramrather than an optical illusion.

There are many types of holograms and optical illusions, often tested specifically for the entertainment world.
There are for example gods live concerts visible remotely via holograms: the signal starts from London and takes less than a third of a second to go around the world and to be projected as a hologram on stage in the United States.
And if these techniques were the new frontier of the industry show?

Holograms, what they are and how the moving ones of Michael Jackson and Whitney Huston work