The Truth About Holography
Episode 2: I Find Your Lack of Depth Disturbing
Holo there! Welcome back to our four-part series where we uncover the truth about holography. In the first episode, we discussed the real definition of holography, the physics behind it, and explained how holographic projections should be made up of multiple depth layers. In this second episode, we’ll take you through the legacy 3D techniques used for cinematic and theatrical performances, as well as discussing current headset technologies and the side-effects they cause.
Current 3D Technologies
Have you ever seen a “3D” film where you would receive a funny pair of cardboard glasses that would have blue and red lenses? That type of cinematography is based on a method called “stereoscopy”, which gives you an illusion of 3D depth, but strictly speaking, there is nothing 3D about it. Stereoscopy presents two images offset on the same screen, each of which is viewed independently by each eye to give that perception of 3D depth. Remember that your eyes are a certain distance apart from each other, so they also view the same screen at two different angles, thus presenting two different images to your brain. Using this concept, along with those classic blue and red lenses (modern lenses are now clear), you are able to see an image on the screen and another that seems to be suspended in front of it. Those lenses acted as light wave filters to ensure each eye sees what is intended. But these are two 2D images, just one appearing on top of the other. The offset creates a 3D illusion, but it is not truly 3D.
Another visual approach presented as “3D” is the “Pepper’s Ghost” effect. It’s a trick that is used in theatres, concerts and museums and is often marketed as holography. Popular examples include recent live performances by both Tupac and Michael Jackson. While the technique can be an impressive stage effect, it is still just a simple 2D project and can certainly not be considered holography. Let me explain.
The basic trick involves an image that is projected from a hidden room (known as the “blue room”) onto a large piece of glass/film situated at 45 degrees between the room and the stage, creating an effect of a “ghost-like” image appearing on stage. Again, this may resemble a holographic projection, but it is simply a 2D image reflected off a transparent surface. The disadvantage is that Pepper’s Ghost projections only look realistic at a certain distance and must be viewed head on, otherwise the flat nature of the image becomes very obvious.
Problems With AR/VR Today
Techniques like stereoscopy and Pepper’s Ghost have found their way into a number of Augmented Reality (AR) and Virtual Reality (VR) headsets, along with the trade-offs mentioned earlier. Genuine 3D holography is able to overcome these issues, offering a much more realistic and natural viewing experience.
It should be said that most “3D holographic” headsets sold today aren’t in-fact displaying true holographic images, nor are they in 3D. While these headsets are able to achieve a level of augmented/mixed reality, they still fall short in achieving natural depth perception. The images you see through such headsets are displayed on a single depth plane — meaning that every individual virtual image displayed will be in focus at the same time (just like on a TV screen). This is unnatural to the human eye — when we view a real object, our eyes bring this object into focus, whilst the surroundings are left out-of-focus. The lack of realistic depth perception causing issues of nausea, eye-strain and headaches, especially if devices are used over long periods of time. The effect also worsens the closer you are to these screens. We will explain exactly why this is the case in the next episode.
In conclusion, a number of “3D” display technologies have emerged that are not able to provide a sufficiently realistic and comfortable viewing experience: due to the lack natural depth perception. We have discussed headset displays and the problems they present, despite their claims of being holographic or 3D. In the next episode, we will explain why an insufficient number of depth planes is responsible to a range of unwanted side-effects. Prepare yourself for some cross-eye diagrams and the Vergence-Accommodation Conflict.