A Guide to 3D Display Technology

8/6/2019 A Guide to 3D Display Technology

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A guide to 3D display technology: itsprinciples, methods, and dangers

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y Share 318 by Devin Coldewey on June 19, 2010

Whether you buy into the hype or not, its plain fact that 3D is everywhere these days.From movies and games to laptops and handhelds , pretty much every screen in thehouse is going to be 3D-capable in a year or so, even if you opt not to display any 3Dcontent on it. Those of you who choose that path may stop reading now, and come back alittle later when you change your mind. Because if you have kids or enjoy movies andgames, there will be a point where youre convinced, perhaps by a single standout piece of media, that 3D is worth it at least some of the time.

But 3D isnt as easy to get used to as, say, getting a surround-sound system or movingfrom 4:3 to widescreen. Why is that? Well, its complicated, but worth taking the time tounderstand. Moreover, like any other new technology, 3D is not without its potential risks,and of course studies will have to be done to determine the long-term effects of usage, if any. For now, though, it must be sufficient to inform yourself of the principles behind it andmake your own decision.


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Lets just have a primer in case youre not familiar with how 3D works in general. There area few major points worth keeping in mind. Well start with the basics. How do you see in 3Dto begin with? Heres a crash course on your visual system.

How depth is determined in your visualsystem

Even if it feels silly, just indulge me here: close just your right eye. Now just your left. Nowyour right. Its like in Waynes World: camera one, camera two. You must have noticed thatthings change position a bit. This, of course, is because your eyes are a few inches apart;this is called the interocular distance and it varies from person to person. Note also thatwhen you look at something close, objects appear in double in the background. Look at thecorner of the screen. See how the chair or window back there is doubled? Its becauseyoure actually rotating your eyes so they both point directly at what youre focusing on.This is called convergence, and it creates a sort of X, the center of the X being whatsbeing focused on. Youve probably seen a diagram like this one before:

So the objects at the center of the X are aligned at the same points on your respectiveretinas, but because of the interocular, that means that things in front and behind of that Xare going to hit different points on those retinas resulting in a double image. You can seethrough the double image because whats blocked for one eye is seen by the other, thoughfrom a slightly different point of view. Experimenting with this always gave me a sort of childish joy: once you start learning the actual optics and wiring of the visual system (as Idid when I was studying it), you lose all compunction about playing with it and viewing yourown minds mechanics in action. Optical illusions are great for this, too.


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Next we have focus. Your eye focuses differently from most cameras, but the end result issimilar. Try holding your finger out at arms length and focusing on it, then on somethingdistant that is directly behind it. Obviously the focus changes, and you may have noticedthat while the distant object was blurry while you looked at your finger, your finger (indouble) was in focus while you looked at the distant object. That has to do with the opticqualities of your eye, which I wont go into here, but its still important. More important,

however, is this: try it again, and this time pay attention to the feeling in your eye. Feelthat? Sort of like somethings moving but you cant tell exactly what? Well, your eyes arerotating a bit, but only a few degrees, in order to converge further out, but moreimportantly, youre feeling your the muscles of your eye actually crush or stretch out thelens of the eye, changing the path and internal focal plane of the light entering your eye.Farsightedness and nearsightedness occur at this stage, when either the lens or the eyeballitself is misshaped, resulting in focus being skewed or difficult to resolve one way oranother.

Once the two images have been presented to yourretinas, they pass back through the optic nerve to various visual systems, where anincredibly robust real-time analysis of the raw data is performed by several areas of the


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brain at once. Some areas look for straight lines, some for motion, some perform shortcutoperations based on experience and tell you that yes indeed, the person did go behind thatwall, they did not disappear into the wall, and that sort of thing. Eventually (within perhaps50 milliseconds) all this information filters up into your consciousness and you are aware of color, depth, movement, patterns, and distinct objects within your field of view, informed

mainly by the differences between the images hitting each of your retinas. Its important tonote that vision is a learned process, and these areas in your visual cortex are

programmed by experience as much as by anatomy and, for lack of a better term,instinct.

Why do I go into all this detail? Well, because I think its interesting. And also because if you want to understand 3D display technology, its probably a good idea to understand yournative 3D acquisition tools.

H ow depth is created in 3D displaysTheres a simple explanation here and a complicated explanation. The simple one first: 3Ddisplays create the illusion of depth by presenting a different image to each eye. Thats it.And thats something that all 3D displays have in common, no matter what. In a fit of uncommon camaraderie among media and electronics companies, standards were evendeveloped that encode a 3D stream similarly to normal stream, except with totally separateleft and right eye images baked right in. There are variations, of course, but its asurprisingly practical approach they agreed on.

But how best to display it? Everyone differs in their opinions. Basically you have threefundamental techniques (and a few outdated or simply unused ones Ill mention briefly) of

sending the right eye image to the right eye and the left eye image to the left eye (RIPL isa Lopes). If you imagine each image to be tailored to its respective eye (its hard tofake), a perfect 3D display would show this:


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In practice that doesnt really happen. Lets take a look at the techniques used toapproximate it.

F iltered lenses

The original. The red-blue, red-green, ormagenta-cyan (or anaglyph, the coolest word in this story after parallax barrier) glassesthat came to symbolize 3D split a black-and-white (and later, color) image into twocomplementary components. I wont get deep into the mechanics of it (Wikipedia hasan excellent entry ) but basically it creates an image where part goes to one eye and partto another, and part to both this last part will be the screens normal plane where youreyes are to focus, and hence receive similar input. Troubles are mainly of the colorperception variety; its extremely hard to balance things so that your brain takes thebroken-up colors and assembles them correctly. However, anaglyph is still in use and stillrelevant I just watched T oy Story 3 using green-magenta and it looked great. A newerversion (by Infitec) uses advanced filters to split each color into two components, sendinghalf the red spectrum to one eye and one to the other, but these havent caught on which ispart of the Dolby3D system (and which somehow Ive managed to avoid entirely and thinkrare).


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The most modern version of filtered lenses (bottom illustration) uses polarization originally linear, now circular polarization (RealD) is used, since it allows you to tilt yourhead without affecting the image. The objection to this tech is that the brightness of theimage is essentially halved. Circular polarization in general is really cool, by the way. Isubmit that a particle may also have a wave-based quantum polarization, fading in and outof existence . But that is neither here nor there. L iterally! Oh, I crack myself up.

Active shutter glasses


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This is the current method of choice for most 3DTV companies. The media is displayed at a high framerate, and the glasses rapidly switchbetween black and clear using a pair of low-latency transparent LCD screens. In this way,one eye sees nothing (for as little as a hundredth of a second or so) while the other sees its

correct image, and a few microseconds later, the situation is reversed: the opposite eyesimage is displayed and the LCDs have switched. The benefit is that each eye is getting the

full image whenever its getting anything (unless theyre cheating and doing it viainterlaced field switching).


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There are a number of objections to this technology:

T he glasses themselves vary in performance. The technology is b eing improved ,and last years glasses are outperformed by this years glasses and likely in a few monthsthey will be out of date. Its not a bad thing that the tech is improving, but considering thenext few point against it, its bad news to implement a technology in flux.

H igh cost. A single pair of these glasses may cost upwards of $100. The cost of adoptingthese as an individual is high enough, but for a theater which must buy thousands andmaintain them, while facing the constant risk of theft, its impractical.

P osition and tilt can affect the image. Im not sure about this one, but it seems thatthe LCD shutters refresh from the top down, like your monitor. Its not done all at once,technically speaking. This can be predicted for or ignored when the head is straight, butwhen there is tilt , you can get bleed of certain portions of the other eyes image, or a


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prismatic effect from the LCDs not being aligned correctly with the screen. There can alsobe interference from the refresh pattern of the LCD. Plasmas reduce this.

P ower is required. LCDs dont run on faith. The batteries in these things need charging,not particularly frequently, but infinitely more so than passive glasses. Furthermore, themachinery and power infrastructure means they can be bulky and heavy, though this isimproving.

A frequency ar b iter is often required. Until some serious standards are established,its unlikely that your glasses, Blu-ray player or set-top box, and TV will all be speakingexactly the same language. And since absolute precision is necessary for the glasses towork correctly (the error must be kept down to fractions of a microsecond), and tinyvariations may occur somewhere along the line, a synchronizing device is often used tocoordinate the signals from the other components of the display. These increase the costof the system and are one more thing to break or replace.

T he flashing LCDs have b een linked to epileptic seizures, among other things. Illgo into this further below in dangers, but for now its enough to know that the risk exists.

As you can see, its quite a list, though some of these flaws are being remedied. Onewonders why so many companies have gotten on board with such a thing. Well, it offersmuch more opportunity for making money, for one thing, and they dont have to modifytheir screens in any way other than increasing the refresh rate, for another saving themprecious R&D money. My personal opinion is this technology will remain on top untilsomeones skunk works research team produces a viable alternative in the form of circular-polarized TV display filters that dont affect the image too much.

Autostereoscopic display

These have been around for a while, at variouslevels of sophistication, and are now in the spotlight as the 3D method used by the Nintendo3DS. You probably saw something of the lenticular lens method (a saw-tooth prism thatdirects light in varying direction) in holographic display in the 90s on a fancy CD jewelcase covers (I remember it from Tools A enima (yeah yeah)). The principle is that by somemethod or another, one pixel or group of pixels has its light directed to one eye, and


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another group to the other. This can be accomplished in a number of ways, but nowadays itis most likely to be a parallax barrier: a series of slits in the display, precisely placed toallow light from every other line of pixels to go one way or the other. Even lines of pixels goright, and odd lines go left, for instance. This enables the image to be split without the useof glasses a benefit not to be underestimated.

As you might expect, there are issues with this method as well.

T heres a relatively small sweet spot. Because the placement of the slits (andtherefore the viewable angle of the affected lines of pixels) is static, you must have youreyes in a certain place in order to perceive the effect. Too close or too far away and lightbegins to leak in from the other set of pixels, or the 3D illusion is destroyed otherwise.

E ffective resolution and b rightness are halved. Because half of the lines are going oneway and half the other, each eye receives half the information that the screen is capable of putting out. This results in reduced brightness and resolution. The 3DSs screen is800240, but the effective resolution is 400240 (giving it a weird aspect ratiosomewhere between 16:9 and 16:10, incidentally). If you want to display 1080p contentusing a parallax barrier, you need a 4K display.

I t requires modification of existing screens. Although I can imagine a parallax barrierfilter for a TV, its never going to happen. The technology must be tightly integrated withthe display, which increases cost. Its also possible that the parallax grill might be variableon large TVs with wide pixel pitch.

Other ways exist of showing 3D on single screens without glasses: the use of twocomplementary displays (in VR goggles or the like), for instance, but these methods of showing two images to the visual system generally make too many compromises in cost orimage quality. For you, there are mainly the ways shown above. I make no secret of mypreference for circular-polarized glasses: theyre cheap and effective, only held back by the


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brightness and lighting method of whatever screen youre using. I think theyll win out inthe end, but as we move on to the dangers, please to remember that the methodsmentioned are more or less equally exposed to these persistent problems.

There is also an ongoing conflict among 3D filmmakers concerning the use of convergenceversus parallel. This is a technical consideration not of general interest, but in the interest of completeness I should say that there are points on both sides. Filming is far, far simplerwith cameras aligned in parallel, but some insist that convergence is necessary to create themore compelling 3D effect. Its far from settled, and I expect to have a separate post onthat in the near future.

Something not in conflict is the quality of films created using 2D-to-3D conversion. TheseFranken-films are a production disaster and the coarseness of their depth cues would giveanyone a headache. Avoid at all costs.

One last note: stereoscopic technologies usually assume good vision to some degree inviewers. A majority of people have some defect in their vision, however, most oftennearsightedness in one eye or the other, or minor astigmatism. This can be difficult to allowfor, resulting in glasses breaking the 3D effect, and of course the necessity of wearing 3Dglasses over ones glasses is a deal-breaker for many. Expect this to be catered to in thenext generation of 3D displays. They have to walk before they can run.

W hy and to whom 3D displays are dangerous


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A couple months ago, Samsung conscientiously issued a pu b lic warning concerning its 3Ddisplays, and by implication those of the competition. This warning probably exists in thedocumentation of every 3D display technology out there in one way or another, thoughsome have it worse than others. Its also probably printed on the back of your ticketwhenever you go see a 3D movie, though I suspect that theaters arent as assiduous asthey could be in screening out preggers and babies from their audiences. View at your ownrisk, I suppose. So why the warning?

Well, in Samsungs case its specific to active-shutter glasses. I mentioned above that theseglasses can produce seizures and other effects. What happens is this: having each eyebeing completely blocked out thirty or sixty times per second is the equivalent of having ahigh-frequency strobe going off in your face. Youre probably aware of the danger thispresents to epileptics and others: seizures, nausea, and fatigue are not uncommon.Furthermore, though this hasnt been adequately investigated to my knowledge, it seems tome that the constant strobing might result in fatigue of your iris and lens muscles, whichare constantly receiving conflicting information. Thats getting better, however: theprecision is increasing and duration of blackout decreasing, which means your unconsciousis less likely to see the blackout.

But there are objections to 3D that apply whether youre using shutter glasses or not (if youd rather have Bill Nye explain this to you, click here ). The issue is simply this: youretricking your eyes and your mind into thinking there is depth where there isnt. But it beginsto look less like a trick and more like a serious deception if we add two things intoconsideration: one, that perceiving depth is an active process that involves muscles andmovement, and two, vision is a learned skill.


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Think back to when you were focusing on your finger, and then on the distant object. Youreye knows that to focus on a more distant object, it has to perform a certaintransformation on the lens in order to bring that object into focus. When you see an objectin a movie, your eye immediately tries to correct for that objects distance by deformingyour lenses but nothing happens! Whaaat? your visual system thinks, That car should

be coming into focus! But it doesnt and it wont for the foreseeable future, and meanwhileevery time the focus changes, or the shot changes, or the camera moves, or the charactersmove, your eye is attempting to refocus, to change its shape. This creates fatigue in themuscles and confusion in the brain.

When you shift your attention and gaze to another (out of focus) object, your eyes alsonaturally change their point of convergence. This occurs when youre watching 3D movies aswell; you can even see with your naked eye the bones of the 3D effect, in that objectsbehind or in front of the plane of focus will be out of phase with each other (theyll appearblurry or in double; the farther from what the plane of focus, the more so). When your eyeschange convergence, they naturally want to change focus, since in a majority of cases,changing the point youre looking at means changing the shape of your lens. Again, though,your eye and brain are tricked, and the act of focusing is not only unnecessary but harmfulto correct perception of the 3D image. So your eyes reconverge but the focus doesntchange an unnatural occurrence, though one that can be minimized by carefulmanipulation of the cinematography and maintaining control over the audiences gaze.

Another effect is parallax, which is the way objects move relative to each other when youmove your head. The dissonance created depends on the distance from the screen, sinceobjects dont move much when you move your head a bit if theyre 40 feet away. But nomatter what, when your eyes move, your brain expects the image to move if its perceivingdepth. [ thanks to the commenters who corrected me on these points ]


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established visual systems, but to those who are still learning. I havent read any of theliterature, and I suspect there is much discussion of when the visual system reaches

maturity, but I think its safe to say that a toddler of 4 or 5 is approaching it but not quitethere. Here danger lies.

If a childs visual system is taught with a significant portion of its input being a virtual 3Denvironment on a 2D physical plane, the brain will form with such a system being

legitimate, possibly to the detriment of normal vision. And this is without reckoning thepotential damage from the lack of visual variety such a child would experience. Im nonaysayer when it comes to digital means of entertainment for kids, but playing outside andin the real world fulfills a necessary part of our physical and mental development. A childexposed to excessive amounts of 3D media may not only develop incompletely due to lackof stimuli, but may develop incorrectly due to the presence of misleading stimuli.

Its a serious consideration, but to be honest, not one that seems to me to be a great risk atthe moment. The proportion of the childs time dedicated to 3D media would have to be

huge, and would probably indicate more pressing problems than choice of entertainment. Itmay turn out that all this worrying was for nothing, but it cant hurt to be educated about it.And its worth mentioning as well that a native understanding (i.e. dedicated brain space)of 3D/2D displays is not necessarily a bad thing. I myself have (if I may say so) rather goodhand-eye coordination and reflexes partially attributable to playing N inja GaidenII and Mario Kart when I was younger. Even so, its worth being aware of what is possibleand why.

W hat you can do a b out it

Unfortunately, theres not a hell of a lot you can do to reduce your risk. The problems areinherent in our own makeup and the fact that 3D displays create only the illusion of depth.What you can do is control your exposure.

T ake a b reak. I know its hard to stop a movie right in the middle, but think of whatyouve read here and how hard it is on your eyes to do what youre doing. There is nothingto indicate that occasional and limited use of 3D has any kind of long-term ill effects. Allthe same, take the same precautions you might use in watching a long movie or doing lots


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of work on your computer. Stand up, walk around, and interact with things in the realworld. Give your brain a break from being tricked. If you feel that you are beginning tolose touch with the real world (this actually happens), stop for at least half an hour. Somepeople are more susceptible to sickness and after effects than others. Know your ownlimits and the limits of others.

Limit kids 3D time. Again, there is little to suggest that moderate use, even by kids, willmake for any serious problems. And Im not going to fabricate numbers here forreasonable amounts of time. But early childhood is, of course, an incredibly importantformative period for basic physical interaction and establishing sensory norms. Use yourdiscretion and remember that viewing 3D on a 2D surface is far more unnatural to a visualsystem (young or old) than plain 2D images, or even 2D representations of 3Denvironments, which are very different.

Dont b uy active shutter- b ased displays. This may necessitate the next tip. Youll savemoney and avoid the potential problems inherent in the system. If you absolutely mustbuy one, do your research beforehand and dont buy cheap. Slow LCDs and shoddy

synchronization are bad for both you and the image. O pt out until 3D gets b etter. All these technologies are being improved at impressive

rates, since all the electronics companies are banking on them as the next big money-maker. Next year will bring better shutter glasses, brighter screens, and possiblyaffordable home polarization. As with any other new technology, the longer you wait, thebetter deal youll get down the line. Early adopters are paying with more than cash(though theyre paying enough of that); theyre paying with the headaches of complicatedsetups, hardware incompatibility, and so on, in addition to the real-life headaches that 3Dseems to bring to nearly everyone at this point. If you really want to see something in 3D,you can always go to the theater.

There you have it. 3D is a promising and powerful tool, and I look forward to watchingmovies and playing games with it once its initial growing pains are over with. Roger Ebertwas impatient enough to condemn the technology at this early stage, and as you haveread, there are plenty of reasons for him to do so. But I have faith that 3D can be appliedtastefully and judiciously by those creating the media, and viewed with moderation and careby those of us who choose to consume it.

A Guide to 3D Display Technology

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