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TV prototype flaunts dark side

Posted: 16 May 2008 ?? ?Print Version ?Bookmark and Share

Keywords:LCD TV? TV prototype? LED backlight?

When the CD was unveiled, one journalist remarked that the most striking thing about a CD's sound quality was its silence. Between the notes, a CD conveyed no hiss, no noise.

The latest analogy to that phenomenon is an LCD TV prototype that Dolby Laboratories demonstrated in April. The most astounding thing about it was how truly black its LCD screen was.

Dolby showed off its High Dynamic Range (HDR) technology at its full potential by using a 46-inch LCD panel featuring 1,838 LEDs for backlighting. The model was prototyped by SIM2 Multimedia, an Italian high-end home theater manufacturer.

Dolby/SIM2, however, was not the first to use LEDs for LCD TV backlighting. Samsung has been shipping LCD TVs with an LED backlight unit based on a technology different from Dolby's for some time.

Although he acknowledged a growing interest in LED backlight units, Chris Chinnock, president of Insight Media, estimated that their penetration in TVs would be only 1-2 percent this year. Asked how Dolby's HDR compares with LCD TVs with LED backlight unit, Chinnock said, "Dolby can do area dimming down to an individual LEDmuch more than anyone else does. Plus, the detail of the area dimming algorithm is much more sophisticated and the brightness levels much higher." In sum, "It's local dimming on steroids."

In the demonstration, SIM2 ran Dolby's proprietary image processing algorithms on a PC to modulate backlighting and LCD crystals.

Unlike conventional LCDs for which the contrast ratio is limited to 450- 650cd/m2, Dolby claimed that SIM2's prototype panel offers brightness greater than 4,000cd/m2.

Local dimming
The electronics industry today recognizes that LCDs have a variety of shortcomings, ranging from motion blur to color reproduction. For example, Bharath Rajagopalan, business line director of image technologies at Dolby, called contrast ratio "the Achilles' heel" of LCD TVs. "Black is not black. A lower dynamic range affects colors in the worst way," he said.

The HDR technology is Dolby's answer, designed to enable better contrast and brightness on LCD TVs with a technique called "local dimming."

Further, SIM2 applied Dolby's proprietary HDR "dual modulation" algorithms for locally dimming backlighting, while modulating LCD crystals.

The end result of the Dolby/SIM2 collaboration is video images in which black is blacker and a finer level of luminance control provides more light intensity, with more "midtones" that add a film-like depth.

LCD screens today, even in their "off" state, never offer truly black screens, as they cannot completely block the backlight illumination.

Approaches to solve this include "global dimming," in which the whole backlight dims for primarily dark images or brightens for predominantly bright scenes. But because most images are of average brightness, global dimming promises negligible improvements in image quality and static contrast ratio.

Dolby's solution, on the other hand, is called local dimming.

"Local dimming consists of two elements," Rajagopalan explained. First, rather than blast an entire LCD with the cold-cathode fluorescent tubes used as backlight in most LCD screens, local dimming deploys solid-state light such as LEDs, which can be locally modulated. Second, local dimming uses Dolby's proprietary algorithms for ? continued from page image processing on both spatial and temporal levels, Rajagopalan said.

Backlight can be divided electrically into several areas, each of which can be independently altered according to the brightness of the image's corresponding section. The higher the number of independent backlight sectors, the better the overall contrast ratio, according to Dolby. By using 1,838 LEDs, SIM2's LCD prototype offers unparalleled contrast ratio and brightness.

Dolby's local-dimming processing: Modulation of individual LEDs or LED clusters improves static, dynamic contrast.

No stranger to video
With HDR, Dolby, best known for its Dolby Digital audio technology, will effectively enter the consumer video market. Rajagopalan insisted that Dolby is no stranger to the video business. The core work of Dolby's founder, Ray Dolby, when he worked at Ampex in 1950s before establishing Dolby in 1965 was in the video domain. "Video was his passion," said Rajagopalan.

In the professional video market, Dolby is already very active in digital cinema. "We design and manufacture servers for digital cinemas," he said. "We developed 3D cinema technology."

Nonetheless, Dolby's HDR technologies are not Dolby's internal invention. A year ago, Dolby purchased BrightSide Technologies to acquire HDR, which at the time was BrightSide's development-stage imaging technology.

Even with HDR, there will be no changes in Dolby's fundamental licensing business model, Rajagopalan said. Like Dolby's audio technologies, HDR will be licensed to OEMs. "We won't be in the business of manufacturing or selling LCD TVs," he said.

LCD performance comparison: Dolby's HDR selectively brightens backlighting of bright areas in scenes.

Boon for LED manufacturers
The element that remains unclear is the cost of HDR-enabled LCDs. "It all depends on such variables as screen sizes, the number of LEDs used for LCD backlighting, cost targets for each LCD TV model and power consumption," said Rajagopalan.

While using more LEDs in an LCD TV for backlighting provides better contrast (as in SIM2's LCD TV prototype), each LED could cost anywhere from "15 cents to $3 to $4," he said.

Noting a growing LED market in recent years, Dolby is confident that LED technical improvements and cost reduction will work in HDR's favor. Beyond licensing, Dolby will help OEMs with HDR-related know-how, Rajagopalan said.

- Junko Yoshida
EE Times

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