The Picture Suddenly Gets Clearer

By Philip Elmer-DeWitt

If all goes according to plan -- a big "if" when it comes to new technology -- broadcast history will be made in a meeting room on Capitol Hill this week. A new kind of television signal will leave the Bethesda, Md., TV tower of WETA, a PBS affiliate, fly across downtown Washington, strike an antenna on the roof of the Capitol building and zip down a cable into the Thomas P. O'Neill Room two floors below. There, before an audience of Senators, Congressmen and assorted commissioners, magician Harry Blackstone Jr. will draw back a black cloth and reveal the first image ever to be broadcast in digital high-definition television: a razor-sharp picture of a fluttering American flag.

The image is well chosen. Just two years ago, high-definition television (HDTV) was a symbol of everything that was wrong with the American electronics industry. After ceding most of the market for today's television sets to Japanese and European manufacturers, the U.S. was about to lose the market for tomorrow's TVs as well. It seemed only a matter of time before U.S. consumers started replacing their squat, fuzzy receivers with crisp, wide- screen sets built around a made-in-Japan technology called analog HDTV.

Now the situation is reversed. With this week's broadcast, the U.S. will seize the lead in the HDTV race, having successfully changed the venue of the battle: from the world of radio- and TV-signal processing, in which the Japanese excel, to the digital world of computers, which is dominated by U.S. firms. "The entrepreneurial spirit is alive and well in the U.S.," says Donald Rumsfeld, former Secretary of Defense and now chairman of General Instrument, the Chicago-based company that spearheaded the push to digital HDTV.

This week's demonstration, staged by General Instrument, marks a victory for those who have argued that the Japanese approach to television design is all wrong, a relic of 19th century technology that dates back to Marconi and Bell. The future, they say, is digital. To survive in a world dominated by digital chips, digital telephones and digital compact discs, the television of the future must speak in the streams of 0s and 1s that are the language of computers.

Conventional TV uses analog waves as electronic representations -- or analogues -- of the light and sound waves captured by television cameras and microphones. The Japanese approach to HDTV was to double the number of horizontal lines used to reproduce the images on the screen -- from just over 500 to more than 1,000 -- while continuing to rely on analog technology to transmit the images.

Scientists have long known that it is possible to represent the information carried in analog waves with strings of numbers. That is essentially what recording engineers did when they replaced analog records and tapes with digital compact discs. The advantages are twofold. Digital signals offer many more opportunities to identify and eliminate distortions caused by interference -- the echoes, flutters, ghosts and bursts of noise that can make today's broadcast television so hard on the eyes. Going digital also makes it easier to isolate and manipulate images -- freeze frames, enlarge pictures, even view scenes from different angles. That feature will grow increasingly important as television and computer technology begin to merge.

The main drawback to representing pictures digitally is that it is enormously inefficient. For all their disadvantages, analog waves are very good at packing a lot of information into a compact form. A single HDTV image, easily captured in a tiny analog wave, represents about a billion bits of digital data -- 100 times more than can be squeezed into the narrow channels of the broadcast spectrum allocated for television by the Federal Communications Commission. It would take a supercomputer at every broadcast station and in every TV set, skeptical experts said, to compress and decompress the data.

Then in June 1990, two days before the FCC deadline for proposing standards for the next generation of broadcast television, General Instrument announced that it had found a way to solve the compression problem. That sent everybody back to the drawing board. Today the Advanced Television Test Center, an industry-sponsored group under contract to the FCC, is considering four different digital HDTV systems for adoption as the U.S. standard: two from General Instrument and the Massachusetts Institute of Technology; one from Zenith and AT&T; and one from a consortium made up of NBC, the David Sarnoff Research Center and the two European electronics giants Philips and Thomson. (Two analog systems submitted by the consortium and the Japanese broadcast company NHK are no longer considered serious contenders.)

How do these systems squeeze 100 channels' worth of visual information into one? The trick is to streamline and simplify the data while taking into consideration what can be seen by the human eye. For example, the eye cannot perceive detail in color as well as it can in black-and-white, and so all the systems save data by transmitting color information at lower resolution. Then, because the vast majority of TV pictures do not change very much from one frame to the next, the systems can eliminate huge quantities of data by sending only the differences between the frames. This process is made more efficient by tracking objects as they move from frame to frame. Finally, when there is too much detail changing too fast for the systems to transmit all the information, the computers simply drop portions of the data -- a truncation that shows up on the screen as fleeting patches of fuzziness. "When the going gets tough," says Robert Rast, a vice president at General Instrument, "the image gets coarser."

General Instrument and the Zenith-AT&T team have submitted working prototypes to the FCC's test center. Although the results are closely guarded secrets, experts privy to the deliberations report that while there have been glitches, no fatal problems have turned up yet in either system -- a fact that will make choosing between them more difficult. "There could be some really tough decisions ahead," says Peter Fannon, executive director of the test center. Fannon is already talking about the possibility that the FCC will want to mix and match technologies from several competing systems. The idea of two or more contenders joining forces is sure to be raised next month, when the proponents gather in Las Vegas for an HDTV conference being held in conjunction with the annual meeting of the National Association of Broadcasters.

When will digital HDTV appear in homes? The FCC is scheduled to pick the winning system in June 1993, and the betting in Washington is that the commission will not miss that deadline by more than a few months. Once the U.S. standard has been set, it will probably be a year before what is now a haphazard collection of off-the-shelf circuit boards -- housed in racks the size of refrigerators -- is reduced to a handful of computer chips that can be sold to manufacturers and stuffed into TV sets. The first commercial receivers could appear on the market in late 1994, but probably will not be widely available before 1995. Prices could start anywhere from $3,500 to $5,000, and will fall slowly until the technology catches on and the sets begin to sell in the millions.

How long that will take is anybody's guess. To create a successful entertainment medium requires not just flashy new technology but also programs compelling enough to persuade viewers to trade their old systems for the new. NHK has been broadcasting analog HDTV signals since 1989, and last November Japan's networks expanded their offerings from one hour to eight hours daily. Despite bold predictions that the Japanese would sell 500,000 HDTV sets a year by 1991 -- and a price cut that brought the cost of those sets from $30,000 to $7,700 -- few people are buying or watching. Things could move faster in the U.S., the home of Hollywood, HBO and Monday Night Football. But digital HDTV is likely to remain a toy for the adventurous -- or the rich -- until the early years of the 21st century.