Digital Cinema: Another Dimension

IMAGE: Disney

Disney's Chicken Little

The moviegoing public loves three-dimensional cinema. When Walt Disney released Chicken Little in 3-D last fall, the 84 screens that showed that version pulled in more viewers than their 2-D brethren at a rate of three to one. Three-­dimensional technology may be the single biggest advantage for theater owners since sound came to the movies, because today you just can’t get that kind of picture at home.

In the film era, the technology never became much more than a gimmick. The quality was never all that good, and it was expensive to produce and display. Still, when available, it attracted moviegoers.

But digital cinema gives 3-D a chance to go mainstream.

In the past, moviemakers delivered 3-D in one of two ways, both of which compromised quality. In 1922, Power of Love was the first full-length 3-D movie that played to a paying audience. This movie used a technique called the anaglyphic process. The method simultaneously displays two views of the image—one for the right eye, one for the left—using colored filters to separate the images.

The moviegoer wears glasses with a red filter in one lens and a blue filter in the other. This attempt to sort out the image does a fairly convincing job of it, but color distortion is inevitable, and the resulting image may be fun but far from believable. It works well enough, however, that it has survived some 90 years; it was most recently used for the movie Spy Kids 2.

The other popular method of producing 3-D movies in the film world uses polarized light. Vertical polarization of the perspective intended to be viewed by one eye distinguishes that image from the horizontal polarization of the other. In one procedure, two independent projectors simultaneously display two views of a single movie, each view polarized according to the eye it represents. In another technique, a single projector displays the two eye views on a split frame, showing them through a prism lens that superimposes the left and right views on top of each other.

Again, moviegoers wear glasses, in this case with lenses of different polarization. Polarized lenses tend to darken the overall image, and aligning the two images properly can challenge theater owners.

The digital cinema world today likewise has two main methods of displaying movies in 3-D. Both take advantage of the fact that Texas Instruments’ Digital Light Processing projectors can run at a higher frame rate than film. As a result, the view for each eye can be shown as a whole frame from a single projector; the projector flashes the image for one eye and then the other, back and forth, perfectly aligned throughout.

Real D is a new company in Beverly Hills, Calif., with a proprietary technology that it calls a Z-Filter. The Z-Filter mounts in front of the projection lens and uses a liquid-crystal panel to polarize the light output. A computer synchronizes the switching polarity of the liquid-crystal panel with the alternating images. Theatergoers wear standard, inexpensive polarized glasses.

The one drawback is that the system requires a silver screen to reflect the polarized light without distortion. Normal movie screens have a matte or pearlescent surface; these reflect light evenly, avoiding the hot spots or glare common to silver screens. Some critics insist that the silver screen spoils the normal 2‑D experience.

Real D’s competitor is an open technology referred to as “active glasses.” Several manufacturers of active-glasses technology, including International DisplayWorks, in Roseville, Calif., are promoting this approach now that 3-D seems to be taking root. The active-glasses system uses glasses in which each lens is a liquid-crystal shutter. An infrared signal sent from the projector tells the shutters when to switch to direct the image to the appropriate eye. Active-glasses proponents claim that the viewing experience is more comfortable, and it doesn’t require a special screen.

The drawback with active glasses is that the active eyewear is more expensive and requires theater staff to collect and wash each pair of glasses before ­reusing them. And some viewers find that rapid switching so close to their eyes is disturbing.

The various companies are racing to promote their systems. Both the Z-Filter and active-glasses systems are likely to survive, with theater owners making their choices based on their perceptions of the tradeoffs and moviemakers distributing to both formats. (Theoretically, the content itself should play equally well on both systems.)

As a result, 3-D will likely become a cinema staple. Said one 3-D developer, “After watching [a movie] in 3-D all day in the lab, when I went to the neighborhood theater to see it with my wife, the 2-D was boring and…well…flat!” —R.W.