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Digital Living Room

Haunted by Ghosts of Programs Past?

Wide-screen TVs help you see the big picture, but if the show doesn't fit the bill? The answer may frost your phosphors.

January 24, 2002|JON HEALEY | TIMES STAFF WRITER

TV manufacturers are wild about wide-screen digital sets, which display movies and high-definition TV shows in their full cinematic glory.

There's just one problem: Most of the programs on local stations and cable networks are broadcast in the boxier format used by conventional TVs. As a result, wide-screen owners must choose the lesser of two evils: They either watch a cropped or distorted picture, or they risk ruining the set's ability to display colors evenly across the screen.

The problem stems from the way most picture tubes, projection sets and flat-panel plasma monitors work. The inside of the tube or screen is lined with thousands of tiny phosphors, which glow red, green or blue when struck by an electron beam. That's where the color in a color TV comes from.

The more a phosphor is heated by electrons, the faster it ages and diminishes in intensity. If all the phosphors in a screen age evenly, the set's picture will fade gradually without distortions. But if a group or pattern of phosphors age faster than the others around it, they could cause ghosts or double images.

"It's what we manufacturers call 'the fish-tank effect,'" said Dave Arland of Thomson Multimedia, the company that makes RCA sets. According to Arland, there was a popular laserdisc that was a video of a fish tank. The fish swam to and fro, but the tank, coral and other decorations didn't move.

If you played the disc for hours on end, the phosphors matching the stationary objects would "burn in" on the screen. As a result, ghosts of the tank, coral and plants would seem to glow on top of other programs.

A similar problem can occur if part of the screen is left black for long periods of time. The phosphors in the black areas won't age at all, so they'll appear brighter than the areas around them when the screen is filled again.

New sets are the most susceptible to uneven aging. High-tech digital light processing and liquid-crystal displays, which don't use phosphors, aren't affected at all.

Obviously, the risks disappear when watching wide-screen programs, which are growing more abundant every day. More than half of the prime-time shows on the digital channels broadcast by CBS, ABC and Fox are in wide screen, as are a few NBC dramas. And about half of the DVDs on the market are available in wide-screen formats, including just about every major new release, Emily Bradley of the DVD Entertainment Group said.

DVDs have been the driving force behind the initial sale of digital TVs, most of which aren't capable of tuning in an over-the-air signal. And the incredible popularity of DVD is the main difference between now and the early 1990s, when set makers made a futile attempt to interest the public in wide-screen TVs.

"For most people, this [burn-in issue] is not a big deal," said Arland of RCA. But he added, "If you spend most of your time watching over-the-air TV, not movies, maybe this is something you ought to think about."

That's because the bulk of the programs on TV fill only 75% of a wide-screen display. Their width-to-height ratio is 12 by 9 (or 4 by 3), whereas a wide screen's ratio is 16 by 9. When centered, such pictures leave a blank bar on either side of the display.

Many manufacturers and some broadcasters, including CBS, automatically fill the blank areas with gray bars designed to age the phosphors evenly with the rest of the screen. Nevertheless, Bill Whalen, senior product and marketing manager for Hitachi Home Electronics, said even that approach shouldn't be used more than 15% of the time.

Arland said RCA got so many complaints about the gray bars used by its initial digital TV receiver, it had to add another option: black bars. But the company also warned customers: "If this is the only way you watch ... you're going to have a burn-in problem," Arland said.

To provide protection for the screen, manufacturers have come up with several ways to fill a wide screen with a conventional-size picture. Unfortunately, all have potentially significant drawbacks.

One way is to enlarge the image electronically, a technique that crops off some of the top and bottom. "You give everybody a haircut, essentially, especially if you're watching the news," Arland said.

Another approach is to stretch the picture, an approach that makes everything look heavier. If a regular TV image makes a person look 10 pounds heavier, as the saying goes, the stretch mode "adds a good 20 to 30," Whalen said.

Finally, Hitachi, Panasonic and other manufacturers have developed a technique that leaves the middle of the picture undistorted but expands a portion on each side. Hitachi's Smooth Wide mode, for example, starts altering the image halfway to each edge, with the sections at the edge undergoing the most stretching.

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