Understanding how 3-D TV operates opens up a world of immersive viewing. Get to know the technology that brings 3-D content to your screen.

Television technology has come a long way since its inception. First, it was the transition from black and white to color TV. Then came larger screen sizes, achieved with innovative projection techniques. In recent years, LCD and plasma screens have advanced so much that you can now buy a sleek, 61-inch (155 cm) TV just a few centimeters thick. And with HDTV, the image quality is so crisp and vivid that it's hard to believe it's made up of individual pixels.

What's the next step in TV technology? Now that you can easily replace an entire wall with a screen and enjoy ultra-high-definition movies, what's the next frontier? The answer might be closer than you think — it could very well be 3-D television.

Audiences were first introduced to 3-D technology in 1922 with the debut of 'The Power of Love.' Whether they viewed it as a novelty or something more profound is unclear, but this marked the beginning of a recurring interest in three-dimensional films.

The next major surge in 3-D occurred in the 1950s, when the film industry unleashed a wave of B-movies using quirky gimmicks to attract viewers. Filmmakers were determined to lure audiences away from their home TVs and back into theaters. Their strategies included everything from installing vibrating seats to simulating electric shocks to staging inflatable skeletons zooming down zip lines. Compared to these, wearing a silly pair of glasses seemed quite tame.

Numerous TV episodes and specials have been presented in 3-D, and there's even a market for 3-D DVDs. However, 3-D has yet to make a major splash in the home entertainment market. But, judging by the most popular exhibits at the 2009 Consumer Electronics Show, we may soon be reaching out to touch the images on our screens.

Let's dive deeper into how we perceive objects in three dimensions.

Seeing in Three Dimensions

Why does an object appear three-dimensional when viewed in real life, but appear flat when displayed on a television screen? What causes this difference, and how does 3-D technology overcome the challenge?

This phenomenon is linked to how our eyes focus on objects. We perceive things by detecting light that reflects off objects. Our brains interpret this light and create mental images. When an object is far away, the light that reaches each eye travels in parallel. But as the object moves closer, the light paths converge, and our eyes adjust to maintain focus. This effect is obvious when trying to focus on something very close to your nose, causing a cross-eyed appearance.

When focusing on an object, your brain processes both the effort required to adjust your eyes and how much they had to converge. This combined information helps you estimate the object's distance. If your eyes converge significantly, it suggests that the object is near.

The magic behind 3-D television and movies lies in presenting each eye with the same image from two different angles. This trick makes your brain perceive depth in an otherwise flat image. However, this also means the convergence and focal points are misaligned compared to real-world objects. Although your eyes seem to focus on two images that appear as one in front of you, they’re actually focusing on a screen that’s farther away. This misalignment can cause eye strain after watching too many 3-D films in a row.

How can you display two distinct images that appear as one? The secret lies in the lenses.

Passive Glasses

In the world of 3-D, there are two main types of 3-D glasses: passive and active. Passive lenses are the simpler option and probably what you envision when you think of 3-D glasses. The classic pair comes with anaglyph lenses.

Anaglyph glasses use two different colored lenses to filter the images displayed on the screen. The most common color combinations are red and blue. Without the glasses, you’ll notice two slightly offset sets of images on the screen — one with a blue tint and the other with a red hue. When you put on the glasses, these two images merge into a single 3-D picture with depth.

What's happening here? The red lens filters out all the red light coming from your television, effectively canceling the red-tinted images. Similarly, the blue lens blocks out the blue images. The eye behind the red lens only sees the blue images, while the eye behind the blue lens only sees the red images. Since each eye sees a different image, your brain interprets it as both eyes focusing on the same object. However, your eyes are converging on a point that differs from the focal point, which remains the television screen. This creates the illusion of depth.

Today, a more common type of passive lens used in movie theaters is found in polarized glasses. When you watch a screen using this technology, you’ll notice multiple sets of images. The lenses filter light waves that are projected at specific angles, allowing only light polarized in a compatible direction to pass through each lens. This ensures that each eye sees a different image. Polarized lenses are gaining popularity over anaglyph glasses because they don’t distort the colors as much and provide a better viewing experience. However, this polarization method is difficult to apply to home theater systems, as it often requires coating the television screen with a special polarizing film.

Now, let's explore active glasses.

Active Glasses and 3-D-Ready Televisions

In recent years, engineers have developed a new method for creating 3-D images on television and in movies. While you still need to wear 3-D glasses with this technique, they don’t rely on colored lenses. This method doesn't distort the color quality of the image as much as anaglyph glasses do, and it doesn’t require a special polarization film on your TV screen. Instead, it controls when each eye can view the screen.

The glasses use liquid crystal display (LCD) technology to actively participate in the viewing experience. They are equipped with infrared (IR) sensors that enable wireless communication with your television or display. As 3-D content appears, the image alternates between two identical sets. The two sets are slightly offset, similar to passive glasses systems, but they aren't displayed simultaneously. They alternate at an incredibly rapid pace. If you watched the screen without the glasses, it would appear as though two sets of images are present at once.

The LCD lenses in the glasses switch between transparent and opaque as the images alternate on the screen. When the right eye's image is displayed, the left eye's lens goes black, and vice versa. This happens so quickly that the flickering lenses are undetectable by the human eye. Because the timing is perfectly synchronized with the screen, each eye only perceives one set of images, just like they would if you weren't wearing glasses.

For years, LCD and plasma screens were not suitable for this technique. The refresh rates—the speed at which a television updates the image on the screen—were too low, causing visible flicker from the glasses. However, today's plasma and LCD displays feature incredibly fast refresh rates, making them ideal for this technology.

The refresh rates are just one factor in making a television 3-D ready. Discover more in the next section.

3-D Ready Televisions

A standard television won't work with active glasses. To make them function properly, the images on the screen must synchronize with the LCD lenses in the glasses. This is accomplished through the stereoscopic sync signal connector, a standardized three-pin connector that plugs into a special port on a 3-D-ready TV or monitor. The other end of the cable connects to an IR emitter, which transmits signals to your active 3-D glasses, syncing the LCD lenses with the on-screen action.

The connector operates using transistor-transistor logic (TTL). One pin delivers low-voltage power, the second pin serves as a ground wire, and the third pin transmits the stereo sync signal.

There are two distinct types of 3-D active glasses that aren't cross-compatible: the E-D and ELSA styles. While both emitter types conform to the stereoscopic sync signal standard, E-D glasses only work with an E-D emitter. ELSA glasses can sync with an E-D emitter, but they won't perform correctly. For example, when the E-D emitter sends a signal for the left lens to be transparent, the ELSA glasses will make the left lens opaque, and the right lens will become clear.

Even with a 3-D-ready TV, emitter, and active glasses, not all content on your screen will appear in three dimensions. Content providers must first adapt the signal for 3-D viewing. While it's possible to convert existing footage into 3-D, some creators prefer to shoot video specifically for 3-D. For now, the easiest method to enjoy 3-D content is by connecting a computer to your 3-D-ready TV via an HDMI cable, then streaming 3-D content from the computer. In the future, more DVD players may support 3-D signals, and 3-D transmissions could become a part of cable and satellite services.

Lenticular Displays

While 3-D technology is certainly impressive, some people still prefer a solution that doesn't require wearing glasses. There have been multiple efforts to create displays that can project images into three-dimensional space. These methods range from using lasers to projecting images onto fine mist or artificial smoke, but such approaches aren't widely adopted or practical.

One method for creating three-dimensional images, often seen in sports arenas or during large conferences in hotels, involves a display coated with a lenticular film. Lenticulars are tiny lenses on the underside of a special film. The display shows two identical images, and the lenses direct the light from each image to a specific eye. Your brain combines the images, and you perceive it as a 3-D image.

This technology requires content creators to produce special images designed for the 3-D effect. They must interlace the two sets of images. If you were to view the video feed on a regular screen, you would see a blurry, double image.

A challenge with lenticular displays is that the viewer must be positioned in a specific spot to experience the 3-D effect. If you move to the left or right of this optimal position, the image becomes blurry. However, once you move back into the sweet spot, the image sharpens. Future televisions may include cameras that track the viewer’s position, adjusting the image to keep them in the sweet spot. Whether this can work for multiple viewers remains uncertain.

Some individuals may experience a sensation akin to motion sickness after viewing a lenticular display for an extended period. This could be due to the extra effort your eyes make in handling the mismatch between focus and convergence. However, the upside is that you won’t have to worry about losing a pricey pair of active glasses.

Will 3-D television emerge as the next major trend, or is it just another fad that will resurface every few decades? It’s still too soon to tell. However, the technology keeps advancing. It might not be long before you instinctively duck when a baseball heads toward the camera.