April 29, 2008 by EH Staff
They light up the storefronts on busy city streets, shine behind the marquees at your local cinema and brighten the screens of LCD TVs. LED (light emitting diode) backlights have spawned a new generation of flat-screen TVs that are brighter, last longer, and consume less energy than units that use traditional fluorescent lights.
Dolby plans to make LED-based TVs even better by developing a technology that tackles one of LCD’s most stubborn problems: contrast. “In typical LCD TVs that use cold-cathode fluorescent lamps for backlighting, the light source is always on,” explains Bharath Rajagopalan, senior marketing manager of high-dynamic-range (HDR) products at Dolby Laboratories. “Because of this and the fact that the LCD pixels are unable to completely block the light that strikes their surface, colors appear washed out and black levels are not low enough to show sufficient detail in dark scenes.”
Dolby’s HDR technology beefs up the blacks and other colors by allowing each backlight to be individually brightened or dimmed according to the brightness of the corresponding section of the image. For example, in areas where the scene is dark, the appropriate LEDs are turned completely off; in other portions of the screen, a different group of LEDs is turned all the way on. The brightness of each LED changes automatically throughout the presentation unlike—globally controlled LEDs, where every backlight adjusts to the same setting.
Local dimming enables HDR-based displays to provide a contrast ratio of 200,000:1 compared with 500:1 for a typical flat-panel LCD TV, according to Dolby Labs. The technology will add a premium to the cost of LCD TVs, says Rajagopalan, however; prices may vary according to the number and type of LEDs manufacturers choose to incorporate into their TVs. Dolby expects several manufacturers to implement HDR technology into LCD TVs this year.
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