We all think we know what a hologram is. After all, most of us have seen—or at least heard about—virtual objects floating in mid-air, whether it’s Tupac at Coachella or Princess Leia being projected by R2D2 in Star Wars. In fact, neither of these were holograms. They are just two examples of numerous technologies incorrectly described that way.
“Real images” as defined by optical physics can be recreated by a holographic display with a massive number of viewing angles of the scene that change with point of view and location. When a holographic display allows you to see around objects when you move your head in any direction, motion parallax is maintained—the ability to view objects closer to us as moving faster than objects that are further away. When reflections and refractions behave correctly, your brain tells you, “this is real.” But to achieve holographic realism, a holographic display must provide high-resolution scene information that changes depending on the viewing angle and location in ways that mimic the real world.
The dream of a real hologram has given rise to a plethora of “nice try but no cigar” technologies claiming to be holographic. Most of the things you see represented as holographic are actually just variations of flat 2D display technologies.
Holograms obey what’s known as the eyeline rule: a real holographic object can only be seen between the viewer’s eyes and a holographic light source. Science fiction can do the impossible but, unfortunately, physics cannot. All true holographic technologies require a display surface to project holographic light. Otherwise, the eyeline rule is violated. Anything that suggests otherwise is just movie magic.
Now to be clear, this is not a judgment against these technologies. Many 2D displays produce great images, as do the derivatives that come from them. However, they are not holographic. So, how do you tell a fake hologram from the real deal? If you think you see light magically freezing in mid-air—spoiler alert—it’s a forgery! The following are well-known examples of technologies that, although they may be interesting to watch, are not truly holographic.
Pepper’s Ghost is an illusion that has been popular in carnivals, museums, concerts and theater since the mid-1800s, when British scientist John Henry Pepper popularized it. Pepper’s Ghost is still going strong. It was used to “resurrect” Tupac at Coachella in 2012 and Michael Jackson at the Billboard Music Awards in 2014, as well as dozens of other posthumous celebrities.
In the above examples, Pepper’s Ghost works by reflecting a 2D image off of a piece of semi-transparent film or surface. It’s one of the roots of the term “smoke and mirrors.” But don’t get taken in. It’s cool, but only as cool as looking at any 2D display in a mirror. And if you reach out to grab it, you’ll break it.
Examples: Vntana, Hologram USA, Musion
Stereoscopic 3D Displays are another illusion. 3D movies and 3D TVs rely on glasses to present two different flat images, one for each eye, with slightly different viewpoints. Motion parallax is not supported, and your eyes focus incorrectly on the screen because every pixel in the left- and right-eye images remains the same, regardless of viewing angle. In other words, as you move around a stereoscopic display, the perceived geometry literally follows you, resulting in distortions and painful disparities. As human beings, our bodies and our eyes are in constant motion, even when sitting still, and any lack of micro-parallax change tells the brain that what we are seeing is not real.
Examples: RealD, IMAX 3D, many consumer 3D televisions
Glasses-Free 3D Displays are also known as horizontal multi-view, parallax-only, or autostereoscopic. These are often dubbed holograms but, at best, they are one-dimensional limited light fields with two or more viewpoints that deliver an illusion of parallax. But this technique doesn’t produce a true object in space nor allow the eye to focus on an image like it would in the real world. This “vergence-accommodation conflict” is a leading cause of headaches and nausea.
Examples: RED’s Hydrogen One phone, Looking Glass, Leia (as included within the Hydrogen One)
Volumetric Displays are similar to traditional 2D displays but have the ability to show 2D pixels within a volume. The concept is similar to a point cloud. The effect can be achieved in numerous ways, including time-sequential volumetric slices, laser ionization, or high-speed rotating elements. The latter are often called “spinny things.” We encourage you not to grab the spinny thing or—seriously—you will lose your hand.
Examples: Hypervsn, LightSpace, Pacific Light & Hologram*
Augmented Reality and Virtual Reality are terms describing head-mounted displays that can be quite immersive. But they don’t create holograms. AR/VR typically couple two flat images of a scene with motion tracking that allows some range of motion parallax to be rendered. However, the limited resolution, narrow field of view, poor optical quality, lack of opacity handling (for AR), problematic motion latency, and inability for the eye to truly focus freely about the volume (regardless of marketing claims) all detract from a realistic viewing experience. Bottom line: head-mounted displays do not project real objects into space.
Further, the separation of content source from display technology is extremely important. While both AR and VR may sample from a holographic dataset coupled with motion tracking, the technology does not visually present a hologram to users, who are still only seeing images on flat 2D displays.
Examples: Magic Leap*, HoloLens*, Oculus
The Future
After CES 2019, Fortune magazine declared, “Holograms May Finally Be Coming of Age.” Today, scientists, manufacturers and entertainment companies are already engaged in developing ways to use real holograms.
The future is here, and Light Field Lab is beyond excited to help build this holographic future together.
In the series of articles that follows, I will share my own thoughts and research into the fields of human vision and cognition, image recognition, photographic (and holographic) history, our fraught relationship with modern technology, and more.
You may agree or disagree with my findings. You may take issue with my conclusions. I don’t think you’ll be bored!
But you may also learn something about the history of images, our increasing dependence on portable devices, and why the tools that are meant to help us get more out of life may instead be closing down important parts of our minds and bodies. And I will explain why I am committed to a holographic future that will help us reclaim our time, our memories, and our lived experiences.
Intrigued? Let’s get started.
Note: *Some displays leverage technologies called holographic optical elements (HOEs). Even though HOEs are produced through holographic means, these are not true holographic displays for all of the reasons stated throughout this article.