Special Report: 3D Video in Pro AV

In part one of a two-part special report, our video expert details how 3D video works and which technologies work best depending on need. 10/14/2010 10:36 PM Eastern

Special Report: 3D Video in Pro AV

In part one of a two-part special report, our video expert details how 3D video works and which technologies work best depending on need.

3D. by now, chances are you’ve heard of it. You’ve probably seen it in a theater, at a trade show, or at your local home entertainment store. For much of 2010, the buzz around 3D has been impossible to avoid, from the long-awaited release of Avatar to ESPN’s 3D coverage of the World Cup soccer tournament. Multimillion-dollar marketing campaigns have been launched to convince consumers they want 3D in their homes. Digital cinemas charge 30 percent to 50 percent more for tickets to 3D movies. The first 3D Blu-ray discs and players are trickling into retail stores. And other TV networks are making plans to show major sporting events and concerts in 3D this fall.

In our market, 3D is showing up in self-contained large-screen displays and front-projection rigs. Manufacturers are touting the advantages of 3D for schools, simulation, home theaters, and large venues. Interface manufacturers tout their “3D compatibility” while software companies are rushing low-cost tools for authoring 3D content on computers.

If all this reminds you of the digital TV transition from a decade ago, it should. The interest in 3D is similar to that of digital TV and the rush of 3D activity has created just as much confusion. Once again, acronyms and shorthand have gotten ahead of facts and education, leaving many would-be customers and solution designers baffled and wondering if there really is a place for 3D in the professional AV marketplace.

The answer is yes, 3D does have a place in our world. It’s not going to replace conventional 2D projection and displays. And not every presentation or video benefits from the 3D format. It is not the next step in presenting visual information; rather, 3D is a subset of digital videoand a very specialized one at that.

In the first part of our special report on 3D in pro AV, we’ll break down how exactly today’s 3D display technologies work and discuss when to use one over another. In part two, coming in the next issue of Pro AV, we’ll delve into real-world applications.

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Special Report: 3D Video in Pro AV

In part one of a two-part special report, our video expert details how 3D video works and which technologies work best depending on need.


3Dor more accurately, stereoscopic imaging—comes in different forms (anaglyph, passive, active, autostereo) and can be used to show everything from black-and-white photographs to feature films and TV programs. The technology attempts to capture the depth cues that our eyes use in the real world and reproduce them on flat video screens.

When we look at objects around us, our left and right eyes see two slightly different views. As we fix on a specific object, both eyes focus on it. Then our brain combines the two offset views into one image (referred to as convergence) in order to process depth information. This two-step process is known as stereopsis and allows us to determine the relative shape, height, width, depth, and distance of objects within our field of view.

We use other visual cues to round out our stereo­scopic vision, including shading (how light falls on an object), textural gradients, interposition, and perspective. Yet another more complex set of cues comes from motion parallax, or how the relative positions of one object to another change as we move past and around them.

The process of interpreting these visual cues is largely intuitive. We don’t have to think long about what we see to determine the size and distance of objects in our field of view. It stands to reason that a stereoscopic display should emulate the visual cues we see every day. Sounds simple, but it isn’t. The reason is that with a stereoscopic display, the focal point is always the screen surfacenot anywhere in front of or behind it. That restricts the degree to which we can accomplish 3D effects. In a person with normal binocular vision, depth cues are created by the difference between what our left and right eyes see, a difference known as retinal disparity, and the ability of our brain to focus on (accommodate) and blend those images into one (convergence).

The difference between what our left and right eyes see is small (unless we’ve got our face right up to the screen). Our mind takes the images captured by both eyes and overlays them in registration, creating a single image. Our eyes focus and converge at the same point, a condition known as zero parallax. In order to create stereoscopic images, we must induce some degree of image parallax to simulate retinal disparity, and then correct it with the appropriate eyewear, resulting in a 3D image.

The degree of parallax is not constant. It changes as objects in a 3D scene move closer or farther away, just as retinal disparity would change in the real world. The best 3D content uses this effect sparingly and mimics the convergence and accommodation processes to minimize eyestrain. The worst 3D content pushes parallax to the extreme, and while that results in some intense in-your-face effects, it also causes headaches, vertigo, and in some cases, nausea.

Special Report: 3D Video in Pro AV

In part one of a two-part special report, our video expert details how 3D video works and which technologies work best depending on need.

There is a maximum parallax limit for 3D displays, and that is when both eyes are looking straight ahead with their axes parallel. This condition is known as positive parallax, and it’s never exceeded in real life. But positive parallax only occurs when viewing objects at a distance, not when viewing objects on a monitor or projection screen.

The opposite condition is negative parallax, where the center axes of the eyes cross over each other. To our brain, this implies that the object being viewed is in front of the screen and is similar to what happens when we look at a pencil that is held just inches from our face. Not surprisingly, viewing images with negative parallax for any length of time results in eyestrain and headaches.

Our eyes normally exhibit zero parallax when viewing electronic displays. So we need some way to induce parallax, to separate the left and right eye images, and then use special eyewear to help the brain re-converge the images as it would in real life. The easiest way is to create dual images with opposite (complementary) colors and pair them with similar glasses. This process is known as color anaglyph 3D and is the oldest and only universal 3D viewing system. The most common color combination is cyan and red, but green and magenta and blue and yellow have also been used.

While color anaglyph 3D works surprisingly well, it has an obvious limitationloss of color resolution. It is, however, the least expensive way to show 3D content because the glasses can be made from paper at a cost of a few pennies apiece when produced in large quantities. Anaglyph has been used extensively to show 3D movies over the past 60 years and there have even been a few DVD and Blu-ray titles released in the anaglyph format.

The second process for creating 3D images is to stack a pair of projectors and equip them with polarizers. The polarizers are either oriented at right angles to each other (linear polarization) or at opposite circular polarization angles (also known as Xpol). Each projector shows only the picture information for one eye and the projectors are aligned to create the correct parallax.

The viewer then wears a pair of glasses with matching polarizers for the left and right eye. In theory, the opposing polarization “twist” between each minimizes unwanted ghost images (or cross talk) from the other projector. In reality, there’s always some cross talk, but if the projectors are set up correctly and the eyewear is matched, we’ll see converged 3D images.

This method is known as passive 3D, and is widely used in movie theaters. Passive 3D can also be implemented on LCD and plasma monitors by applying a layer of circular-polarized material directly to the screen surface, aligning it with the rows of pixels. Every other pixel row has the same polarization twist, so the left eye sees the odd-numbered rows of pixels and the right eye sees the even-numbered rows. Our eyes converge these two sets of images into one using depth cues.

The third process for viewing 3D requires more horsepower, and is known as active-shutter or active-refresh 3D. In this system, individual frames of left- and right-eye information are sequenced at a very fast frame rate, typically double the rate used for normal TV. At the same time, a synchronizing signal is sent by the display or an outboard transmitter to a pair of special, battery-operated 3D glasses. These glasses contain miniature LCD panels that switch on and off at the same rate as the left and right eye sequencing of the 3D display. In this way, only one shutter is open in any given instant, revealing to that eye only the image that it should be seeing. Because of our persistence of vision, we don’t notice any flicker at this fast frame rate; the left- and right-eye images appear to be present simultaneously. As with the other methods, our brain then converges the two images into one to create the illusion of 3D.

Special Report: 3D Video in Pro AV

In part one of a two-part special report, our video expert details how 3D video works and which technologies work best depending on need.


What’s the best means of delivering the 3D effect? As AV pros know, there are a number of display technologies in use todayfrom direct-view displays, such as monitors and televisions, to projection displays, such as front and rear projectors.

We can further break down display categories by imaging method used. The first group is emissive displays, where a burst of light energy is viewed directly. The emissive category includes plasma display panels, cathode-ray tubes (CRTs), organic light-emitting diodes (OLEDs), conventional light-emitting diodes (LEDs), and lasers.

Of these technologies, only plasma is in widespread use today. CRTs are being phased out and OLEDs are still a few years away from mass production. LEDs, such as those used in large-scale digital signage, are not practical to use in 3D applications. Lasers can create the required parallax and are capable of fast switching times, but isolating the left and right eye information is difficult.

Transmissive displays, also known as light-shuttering displays, include LCDs of all shapes and sizes, including large TFT LCDs used in monitors and televisions and smaller high-temperature polysilicon LCDs used in front projectors.

Finally, there are reflective displays, including liquid crystal on silicon (LCoS) and DLP. These technologies are popular for showing 3D movies.

For active-shutter 3D applications, emissive displays such as plasma are generally the best choice. They can switch quickly enough between states to keep up with the rapid refresh rates required for active-shutter 3D viewing. The limited number of 3D tests using OLEDs show they too can keep up without modification. Emissive displays always have the widest viewing angles, as well as consistent black levels, brightness, contrast, and color of gray over all viewing angles.

Transmissive displays, specifically LCDs, require the liquid crystals to move from one position to another in a short period of time in order to show video at rates of 60 frames per second or faster. This is not easy to do; many LCD monitors and TVs exhibit motion-blur problems, and techniques such as black-frame insertion are used to minimize the effect. Current evidence shows that frame rates of at least 240 Hz are required to show fast motion in 3D with a minimal level of blur—a tall order for current LCD technology.

That said, large LCD monitors have one advantage: They are much brighter than plasma, which is helpful for overcoming light loss caused by wearing 3D polarized glasses. LCDs have also been equipped with circular-polarized microfilters for direct-passive 3D viewing through inexpensive glasses, a solution favored by 3D content producers.

Projectors that use 3LCD technology face similar limitations and (for now) are better suited to showing passive 3D images through two stacked and precisely aligned projectors that are equipped with linear or circular polarizers.

When it comes to reflective displays, DLP currently has the upper hand. DLP can switch its tiny mirrors thousands of times per second with no motion lag or smearing, making it the preferred choice for 3D digital cinema. Variations on the same chip are used in single-chip and three-chip projectors for home, business, education, and large venue applications. DLP technology is also found in rear-projection TVs and projection cubes.

LCoS panels can be used for 3D, but their switching times are similar to those of LCDs and they have a harder time showing active-shutter 3D. Like LCDs, LCoS projectors are better suited to passive 3D applications, operating in aligned stacks and equipped with linear or circular polarizers.

Next Steps

Whichever way you plan to build a 3D display system, your work is far from done. You also need to ensure that the application (visualization, engineering, education) actually benefits from 3D imagery. and that the content and signaling infrastructure working in the background matches the display technology you’ve chosen.

Fortunately, there are industry standards groups coalescing around ways of delivering 3D content using methods such as frame-packed, side-by-side, and top-bottom encoding. But best of all, there are, indeed, pro AV applications of 3D technology available today. Stay tuned.

Special Report: 3D Video in Pro AV

In part one of a two-part special report, our video expert details how 3D video works and which technologies work best depending on need.

The Pro's 3D Toolbox

Who's making 3D video products that might rise to the level of pro installations? In addition to Digital Projection and Da-Lite (pictured), several companies have their eyes on commercial projects. Among them are:

Barco. The company has implemented its stereoscopic 3D projectors, such as the three-chip DLP Galaxy 12 HB+, into a variety of display systems for visualization, engineering, and scientific research.

Christie Digital. The company also has roots in visualization and sells 3D projectors for digital cinema. Last summer it deployed CP2000 Series and Solaria Series 2 DLP projectors to show World Cup matches.

JVC. Products like JVCs new GD-463D10 LCD color monitor with an Xpol glass filter were built for the professional market. It uses circular polarization system so as not to rely on active-shutter glasses.

Mitsubishi. As Mitsubishi has been pushing its 3D DLP Home Cinema TVs to screen sizes up to 82 inches, the company has also rolled out energy-efficient laser-based models like the 75-inch LaserVue TV and pro-grade 3D-ready DLP projectors, including the XD600U.

NEC. Like Christie and Digital Projection, NEC also plays in the 3D cinema market with products such as the NC2500S-A and NC1600C-A projection systems.

Panasonic. Plasma may be back in vogue thanks to its ability to keep up with fast frame switching. Panasonic makes everything from pro 3D cameras to active-shutter glasses, to 3D production monitors (including LCD)–to say nothing of its large-format plasma 3DTVs.

Sharp. Its PG series of conference and classroom projectors is 3D-ready using DLP-Link technology, which works with compatible 3D content, the right graphics card, and active-shutter glasses, Sharp also makes 3D LCD TVs, such as the new LE925 Series.

Sony. Sony boasts end-to-end 3D technology, from acquisition to display. Its 4K resolution SXRD projectors create 3D cinema experiences; its processors, such as the MPE-200, optimize 3D content; and the company has even demonstrated a 280-inch 3D LED wall.

Stewart Filmscreen. Stewart’s Silver 3D is a commercial screen material for optimizing stereoscopic, two-channel 3D, rear-projection display systems. Its innovative StarGlas 60 and TechPlex 150 acrylic surfaces work well with passive-3D, rear-project systems.

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