Update: Please tear your eyes away from the blue lady and also read this follow-up post. It turns out things are worse than I thought. Now back to your regularly scheduled entertainment.
I somehow missed this when it was hot a few weeks or so ago, but I just found out about an interesting Kickstarter project: HOLOVISION — A Life Size Hologram. Don’t bother clicking the link, the project page has been taken down following a DMCA complaint and might not ever be up again.
Why do I think it’s worth talking about? Because, while there is an actual design for something called Holovision, and that design is theoretically feasible, and possibly even practical, the public’s impression of the product advertised on Kickstarter is decidedly not. The concept imagery associated with the Kickstarter project presents this feasible technology in a way that (intentionally?) taps into people’s misconceptions about holograms (and I’m talking about the “real” kind of holograms, those involving lasers and mirrors and beam splitters). In other words, it might not be a scam per se, and it might even be unintentional, but it is definitely creating a false impression that might lead to very disappointed backers.
Have a look at exhibits A and B (Figures 1 and 2), taken from various sites reporting about this project, and, I assume, PR material released by the people behind the project. They are blatant lies. The technology described on the Holovision web site can definitely not produce what’s shown in these concept images (because that would be impossible). Look at the actual description of the Holovision technology. What’s the first thing they write about, and what’s in the first figure? A screen. A very clever screen, at that: each pixel is not a simple light emitter, but an active element that can emit different amount of light in different directions, somewhat like a lighthouse or the kind of laser used in a laser light show. Having a screen of such active pixels can indeed create what the Holovision site claims: glasses- and head-tracking-free, multi-viewer, holographic 3D. It’s very difficult to make look good in practice, but it’s feasible.
Think of a lenticular autostereoscopic 3D display, as you can buy it today. It uses lenses glued to the display to send the light from alternating pixel columns towards the left or the right, respectively. If you take a properly generated stereoscopic image and interleave it so that the left/right views map to the left/right pixels, respectively, and if the viewer’s head happens to be positioned so that her left eye is in the left projection zone, and her right eye in the right, then she will indeed perceive three-dimensional virtual objects. Holovision takes this idea to the max by creating not just two, but many (hundreds, maybe) of such viewing zones. So no matter where the viewer is, her eyes are always going to get the view that they should be getting, leading to apparently solid, touchable 3D objects, i.e., holograms. So far, so good.
Given that, why do I think the Kickstarter project misleads people, intentionally or not? Primarily because of Figures 2 and 3. Seeing those, and reading “life-size, free-floating holograms,” what would you expect to get? Probably a small projector, like the one shown in Figure 2, that can create apparently solid objects anywhere inside the surrounding environment, like a small car on your hand. Sorry, you can’t have that. Not yours. Let me quote a random article (from Übergizmo, emphasis mine:)
HoloVision could pave the way to such a future, where this Kickstarter project claims to deliver a free-floating, life-sized image that will hover eight feet from its projector, clearly making good ol’ R2-D2 obsolete with his rendition of Princess Leia.
That’s exactly the kind of misconception I’m talking about. Note that the Kickstarter project description doesn’t seem to actually make the bolded claim — it doesn’t have to. Creating a concept image like Figure 1 and tapping into the myth do the job just fine.
Here’s the reality of it: in order to see a hologram, be it a Holovision one, or one on an autostereoscopic display, or a head-tracked 3D TV or whatever, there needs to be a screen behind it. Yes, even “real” holograms need screens (or rather holographic plates) behind them (but usually in front of them). Holographic projectors do not exist, and cannot exist. They are a common misconception propped up (lame pun intended) by their ubiquity in science fiction movies, Star Wars: A New Hope being the prime (and maybe ur?) example (see Figure 3).
This means the Kickstarter’s appeal of life-size free-floating holograms without screens is an internal contradiction. In order to have a life-size hologram, you need to have a life-size screen behind it. Why? Because light travels in straight lines (more or less, at least). What I mean to say is that this is not just “ambitious,” or “far thinking,” or “technically hard;” this is impossible, at least until we invent a completely new set of natural laws. See Figure 4 for a simple diagram.
In order for the viewer to perceive the head of the virtual person in Figure 4, some photons must enter the viewer’s eyes coming from the direction of the head, along the red line. But where do those photons come from? If they come from the “holographic projector” at the right, then they must have changed direction in mid-flight somehow. Photons don’t do that unless they bounce off something solid, and thin air won’t qualify (and a fog-screen display is decidedly not what the Kickstarter project promises). The only possible source for photons entering the viewer’s eyes from the required direction is a light source behind (or in front of) the virtual person, anywhere along the red line. Like, for example, a big fat life-size screen behind the object. In other words, a CAVE. Or two small screens right in front of the viewer’s eyes. In other words, an Oculus Rift. With the setup in Figure 4, the only part of the virtual person the viewer will actually see (indicated by solid color) is its intersection with the pyramid formed by the screen rectangle and the pupil. The rest simply won’t be there. If that part is all you want to see anyway, fair enough, but that’s just you.
In all fairness, there is a way to do what I just said can’t be done: you can zap air molecules with a strong focused laser, leading to plasma excitation that essentially turns a tiny sphere of air into a light source. But that’s not what this Kickstarter project is about, and it can’t create opaque objects. Here’s what backers will really get from the Kickstarter project:
Note how the virtual object on the tiny screen doesn’t look all that 3D, because the camera doesn’t move (to create the illusion of three-dimensionality in a 2D video, you need motion parallax like in this video). Note that, if viewed with the naked eye, the object would appear somewhat 3D. That much is true. But why is the camera not moving? Because as soon as it moves enough so that the virtual object is not located between the screen and the camera any longer, the object will disappear — just like a “real” hologram would. For more money, the Kickstarter project promises a 17″ version of the same thing, which could create, guess what, free-standing objects up to about a foot in size. Which, don’t get me wrong, would be really cool to have — but is it what you thought you paid for?
Multi-viewer glasses-free holographic displays have obvious benefits. They also have drawbacks — look at the rather poor image quality that’s achievable right now, and there’s the problem of how many viewing zones can be maintained, especially with real-time dynamic content. It’s bound to get better, but it’s something to consider. If you don’t mind glasses, or rarely have multiple people looking at your screen, the lower fidelity, poorer 3D, and higher cost might not be worth it.
Finally, why does this bother me enough to write 1516 words on it? Because as someone who builds holographic displays, I’m encountering and fighting this misconception all the time, and I wish it would finally go away. Yes, “real” holograms have benefits over the displays with which I’m working — no glasses, multiple viewers, proper accommodation, no lag — but for practical applications those are far outweighed, at least for me, by low resolution, low color fidelity, and extremely high computational cost to make them dynamic. And even if those problems were solved, you’d still need big screens. And please stop sending me business proposals relying on or building holographic projectors like R2-D2′s, at least until you describe in detail how you will make photons change course mid-flight.