Randy Hoffner /
08.25.2010 11:20 AM
3DTV: Is It the Next Big Thing?

Is 3DTV the new HDTV, or could it be, as suggested by a friend, the next Teletext?

Possibly some readers have not been around long enough to remember Teletext, a method of transmitting text and pictures on an NTSC signal using the vertical blanking interval. And don't tell me you don't know what the vertical blanking interval is! Teletext cropped up in the early 1980s; was transmitted by two networks in the United States; then just went away, as it was a technology that never found a real audience.

At this juncture, at least a couple of major broadcast organizations, including the venerable BBC, are taking a "wait and see" approach to 3D; while others, like ESPN, are creating entire 3D cable networks.

LOOKING BACK

3D appeared in the movies in the 1930s and flourished for a time in the 1950s, when it was applied to some low-rent horror films like "House of Wax." If the reader has been around long enough to remember SCTV Network from the 1980s, you might remember "Monster Chiller Horror Theater" with Count Floyd, which presented such features as "Dr. Tongue's 3D House of Stewardesses," which, incidentally was not in 3D, but which might serve as instructive history, as well as amusement.

Along with 3D horror movies, there were also 3D comic books in the 1950s. These films and comics used a form of three-dimensional-appearing presentation called anaglyphic 3D. This is the old two-color 3D technique where the Z-axis, or depth, is depicted by printing or filming two slightly offset versions of the same image material, simulating the image each of our eyes would see in three dimensions, then superimposing them with the offset. The two-image versions are predominantly rendered respectively in two complementary colors.

The imagery is viewed using glasses holding a lens of each of the two image colors. The differently colored lenses cause each eye to predominantly see only one of the two offset images. The human visual system integrates the two images into a single image, which appears to have the depth dimension. This technique works, but is a little "in your face," no pun intended, and it has some difficulty with true color-rendering.

In the old days, because of technological limits involving the dyes, these two colors were typically red and blue, and we have all seen the classic photographs of a movie audience wearing red and blue 3D glasses.

Anaglyphic 3D is still with us today, now using red and cyan coloring rather than red and blue. It is now possible to make inexpensive, color-stable red and cyan filters for the lenses of these glasses, and the quality is said to be improved over the old red and blue.

The two-color glasses approach, and other approaches, such as use of polarized lenses, employ stereoscopic techniques, which involve shooting imagery with two side-by-side cameras, the lenses of which are separated by approximately the distance between a pair of human eyes. This is called stereoscopic vision, and it may be considered analogous to two-channel stereophonic sound.

THE PULFRICH ILLUSION

Another way to create the illusion of three dimensions was demonstrated to the technology staff at a network where your author worked in the 1980s. The "inventors" of this 3D technology touted it as requiring no special production equipment besides some sort of filter on the camera lens (a red herring, as it turns out). They handed us glasses that appeared to have a dark lens for one eye and a clear lens for the other eye. They showed us some footage and the 3D illusion was definitely there. They were quite secretive about the details of their technology.

After the demonstration, one of my colleagues, a mathematician, said, "Wait a minute, this is the Pulfrich Illusion." He went downstairs to the camera shop in the lobby and bought some neutral density filters. By holding a neutral density filter over one eye, we were able to see the 3D effect using images captured by a plain old TV camera that was being evaluated in the Technology Lab, as long as certain conditions were met.

3D-lensed audience at 2010 NBA All Star Game, Dallas
The Pulfrich Illusion was first described in 1922. It works too, but as stated, some conditions must be met when producing the images. The illusion of three dimensions is created by a timing difference in the perception of the same image by each of the two eyes. The Pulfrich Illusion is a psycho-physical method of creating the perception of 3D. The neutral density filter over one eye simulates the function of an optical delay line, effectively delaying the perception of the image seen through the ND filter.

This is thought to happen because the human visual system responds more quickly to bright stimuli than to dim ones. This effect has also been known to occur spontaneously in people afflicted with cataracts or with multiple sclerosis.

One drawback to this effect being used to create the illusion of 3D is that in order to see the depth illusion, the perceived imagery must be moving laterally across the visual field of the observer, and the darker lens must be on the correct eye with respect to the direction of motion, i.e., left-to-right or right-to-left. Thus, the 3D effect can be observed in particular imagery moving across the screen in the proper direction, but if the motion stops or the glasses are reversed, the 3D effect is lost.

Subsequent to this demonstration, Pulfrich Illusion 3D has been used several times on television for special commercials, and for some special program segments. It has the advantage that the subject video material looks perfectly normal to the viewer who is not wearing 3D glasses, while colored-glasses 3D video looks pretty horrible to the viewer not wearing 3D glasses.

The searches for perfect 3D movies and 3DTV have been with us for almost as long as movies and TV have been with us. But beyond the horror movie applications in the 1950s, and the fact that, for the entire history of the television medium, someone has popped up every once in awhile with a new, or not so new, scheme for 3DTV, it has not yet established a foothold, save for the occasional gimmick.

Today, we have some new digital technologies to draw on to create the illusion of three dimensions in the cinema and on television. We have a new 3D push by movie producers. We also have new 3D television networks being announced, and live sports being aired in 3D. And we have manufacturers offering 3DTV sets for sale at prices that are reminiscent of those for the earliest HDTV sets. It remains to be seen whether the public will, after recently buying a new HDTV set, step up and shell out for a 3DTV set.

This has been a largely historical look at 3D. Next time, we will look at some of the more sophisticated and futuristic ways of generating the illusion of three dimensions from a flat screen.

Randy Hoffner is a veteran of the big three TV networks. He can be reached through TV Technology.



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