3-D TV

Continuing our inspection of the media room of the future, we might be surprised to find a pair of odd looking glasses on the shelf next to the TV screen. On closer inspection, it turns out that these glasses look somewhat familiar they are the kind you wear to see.' 3-D. Three dimensional television transmits images that seem to extend beyond the screen. As we shall see, interest in 3-D seems to come in cycles. A great deal of enthusiasm will be generated about the technique only to have that enthusiasm dampened by technical problems or viewer apathy.

History

Most 3-D viewing systems depend on binocular vision to create an illusion of depth. When you see an object from a slightly different angle, as happens when you see something from your right and left eye, a sense of depth, called stereopsis, is the result. This phenomenon has been recognized for many years. Back in 1833, the stereoscope, a device resembling the View Master toy that is still popular today, was invented. In the 1920s, motion picture producers experimented with a 3-D technique in which one view was filmed using a red filter and the other view filmed with a blue filter. Viewing the scenes while wearing glasses with similar filters produced the 3-D effect. Unfortunately, since color was used to separate the images, this technique could only be used with black and white films.

The real boom in 3-D movies occurred in the 1950s when the red and blue filters were replaced with polarized filters that allowed color 3-D films to be produced. Motion picture companies accepted the new technique with enthusiasm since they were looking for something unusual that would draw people away from their TV sets and back to the theaters. Three dimensional epics such as Bwana Devil and House of Wax generated some audience interest, but the novelty soon wore off.

The technique resurfaced occasionally during the next three decades. A couple of X rated films were released in 3-D during the 1970s and a few TV stations broadcast some 3-D films as promotional experiments. In the mid 1980s, a major Hollywood film, jaws 3-D, failed to rekindle interest in the technique. Nonetheless, the idea keeps resurfacing. Thanks to some technical advances, the late 1980s saw the arrival of 3-D video games, a 3-D camcorder, and 3-D computer screens. ABC even announced that part of the 1988 season finale of its then popular series, "Moonlighting, " would be broadcast in 3-D. Hopping on the bandwagon, the Coca Cola Company announced it would distribute 40 million pairs of special glasses that would enable viewers to see the program and a commercial for Coke in 3-D. (Unfortunately, a writers' strike made it necessary to cancel that particular episode. Coca Cola, worried that those 40 million glasses might go to waste, eventually aired their 3-D commercial during the Super Bowl.)

Technical Considerations

There are two techniques that produce 3-D TV: those that use glasses and those that don't. Let's put on the glasses first.

We've already described the anaglyphic method the one that uses red and blue filters and glasses with red and blue plastic tenses. This technique creates acceptable 3-D for motion pictures, but it loses something in the translation to television. First, television sets vary in the brightness of the images they produce partly a function of the age of the screen and partly the way in which the TV set is adjusted and bright images are essential in projecting anything through the colored plastic of the glasses. If the set can't match the brightness levels in the original, the 3-D effect is much less. Second, the colors of the plastic lenses don't exactly match the colors that are reproduced on the TV screen so one receives a distorted view. Finally, watching anaglyphic 3-D is OK on a big movie screen but viewing for an hour or so on the smaller TV screen causes eyestrain and headaches for many people.

The method that uses polarized lenses was also mentioned. Two images of the original scene are shot. The viewer wears polarized glasses with one lens that permits only vertical polarized fight to enter while the other permits only horizontally polarized fight to reach the eye. Thus, one eye would see one image and the other eye would see a second image, thus creating the stereopsis. Once again, this method works better for motion pictures than for TV. Movie projectors give off polanized light; TV screens don't. In order to get the polarization effect from TV, polarizing sheets must be placed over the TV set's picture tube. These sheets filter the light so that it travels in thin planes at right angles to one another. A mirror then superimposes the two images at the viewer's eyes. The polarized glasses worn by the viewer ensure that the image meant for the right eye is blocked out by the left lens and vice versa. Unfortunately, the viewer must sit perfectly still since slight head movements can ruin the 3-D effect.

A new 3-D technique using liquid crystal glasses was developed in the late 1980s by manufacturers of computer games. The screen displays left and right views of a scene sequentially, a split second apart. The liquid crystal glasses are connected to the screen by a thin wire and tiny electric currents, synchronized to the alternating images on the screen, cause one and then the other lens to darken. Thus, when the view for the left eye appears on the screen, the right lens turns dark. When the right view appears, the left lens turns dark. All of this happens incredibly fast each eye receives a new image every 1/3oth of a secondand the rapid switching creates the 3-D effect. The problem with this system is that the images tend to flicker a bit, which some people find annoying. And, of course, you have to be wired up to your computer or TV set in order for the system to work.

Creating 3-D TV without glasses is harder to do but scientists are examining some possibilities. You've probably already seen one method if you've ever seen a 3-D postcard, or panoramagram. as it's technically called. This method uses singlesided lenticular screens that have vertical lenses arranged in such a way that they resemble a piece of corduroy fabric. A number of vertical strips representing slightly different views of the scene are carefully positioned behind the screens. Each vertical strip of lens is positioned so that light rays are refracted (bent) in such a way that one image goes to the right eye and one to the left. Scientists are trying to adapt this technique to TV by using a double lenticular screen and two projection tubes which beam images to the back of the screen while the viewer watches the front screen. This technique, however, is plagued by numerous technical problems.

The Japanese have used a trick of perception called the chromastereoscope effect to produce 3D without glasses. Chromastereoscope takes advantage of the eye's inability to focus on the three primary colors at once. The muscles of the eyes must change to see these colors just as they make adjustments to view objects at close range or to squint to see something at a distance. The system works adequately for cartoons where it is possible to control the colors. The background can be a primary color, the middle a second primary, and the foreground a third, but real life, where colors are blended, isn't so easily controlled. Thus, the system has limited utility.

Of course, the ultimate answer to 3-D TV may come from holography. Holography is threedimensional, lenseless photography that makes use of laser light. Holograms, the pictures that are produced by holography, are true three dimensional recreations of the original objects that can be viewed without glasses. When you look at a holographic viewing surface, the image appears to hang in space either behind or in front of the view ing surface. You have probably already seen some simple holograms. They are used on credit cards to guard against counterfeiting, and they have appeared on magazine and book covers.

Scientists at the Massachusetts Institute of Technology (MIT) are experimenting with holographic TV. They have yet to transmit an acceptable image primarily because of the enormous amount of bandwidth or frequency space that is needed. Recall that the width of a normal TV channel in the electromagnetic spectrum is 6 mhz. The simplest form of holographic TV ("holovision"?) needs 500 mhz of space. Then there is the problem of projecting the holograms in the home. In order to see motion, thirty different holograms must be transmitted every second, requiring equipment that has yet to be invented. Nonetheless, the MIT scientists are optimistic. They point out that holographic TV is now at the point where broadcast TV was in 1923. It may take many decades, but they think holographic TV will one day be in every home.

Applications

The biggest application for 3-D is entertainment. In addition to its uses in motion pictures and commercial television, 3-D has come to home video. Toshiba sells a video camera and a recorder suitable for 3-D home videos. The Toshiba system uses the liquid crystal glasses and has an adapter that connects to the home TV. The system, which sells for about $3000, creates a striking 3-D effect but the picture must be viewed in a darkened room for maximum results. Sega, Nintendo, and Atari have 3-D video games that also use the liquidcrystal glasses.

3-D TV is also appearing on the corporate scene. Engineers designing automobiles and aircraft use 3-D monitors to see depth on their computerized mock ups. Pilots use large projection 3-D screens in their simulators for greater training realism. Surgeons are investigating the use of 3-D training videotapes for training new members of their profession.

The scientific community is finding new ways to use 3-D TV. Oceanographers have mapped the ocean floor using 3-D videotapes, and the robot that cleaned up the Three Mile Island nuclear power plant was equipped with a 3-D camera that functioned as the machine's "eyes."

Forecast

In the short term, it's unlikely that 3-D TV will become the most popular form of TV watching. The inconvenience of wearing special glasses is the biggest barrier for consumer acceptance. Additionally, 3-D programs are more expensive to produce because of the extra cameras and processing involved. So far, no major production company is betting on 3-D as the wave of the future. In all probability, 3-D TV viewed through glasses will remain a novelty that will resurface from time to time for special events, such as Coke commercials, or for special uses, such as video games.