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A New Display Lengthens Gadget Life

Novel pixel arrangement and a dynamic backlight could save power.

Cell-phone and laptop batteries could last up to 50 percent longer, thanks to a new type of display technology that’s being developed by Clairvoyante, a company based in Cupertino, CA. Clairvoyante announced last month that it was introducing technology that could allow cell-phone, digital-camera, and laptop makers to develop power-saving displays that could dynamically adjust their backlight and color intensity based on the color and brightness of the content.

Pixel placement: Clairvoyante’s display technology (right) adds white pixels to the traditional palette of red, green, and blue (left). This new display also has larger pixels. Together, the size difference and the addition of white pixels let more light shine through so that the backlight can be turned down, saving power.

Altering the intensity of a screen’s backlight isn’t a new idea. For instance, the forthcoming iPhone will include light sensors that determine how bright the backlight should be. But Clairvoyante approaches the problem from a different perspective. Its displays are based on a novel pixel architecture, which it calls PenTile: a pattern of red, green, blue, and white pixels (conventional displays rely on red, green, and blue only) combined with image-processing algorithms to adjust the brightness of individual pixels. By adding the extra white pixel into the mix, says Clairvoyante CEO Joel Pollack, a PenTile display gives brighter whites, darker blacks, and sharper fonts–a feature especially useful for small, handheld screens.

Pollack says that the PenTile pixels are 33 percent larger than conventional pixels. Because the pixels are larger, more light gets through. “Often we double the amount of light throughput,” Pollack explains, “so we can run at twice the brightness or half the power.” PenTile–which Pollack expects to first appear in products by early 2008–also includes algorithms that perform a “sharpening routine” to eliminate any sort of fuzziness around edges as well as moiré patterns, or image defects, that would normally come from the pixel arrangement.

In many cases, PenTile displays look better than traditional red-green-blue displays, says Pollack, but sometimes they don’t. Icons and some graphics in user interfaces and Web browsers can employ colors that “wouldn’t appear in nature,” he says, and PenTile has a difficult time recreating them. But because each pixel is individually controlled, it’s possible to turn down the white pixels, while turning up the backlight so it looks more like a typical red-green-blue display. This could be useful, Pollack says, in the case of someone building a cell phone that would run video–which could take advantage of all the PenTile pixels–and that would run conventional Web browsers or calendars, in which the backlight is turned up and white pixels are turned down.

Another power-saving technology that Clairvoyante is developing is designed to adjust to the brightness of a video as it is playing. Pollack explains that the chip that drives the display contains a number of logic gates dedicated to analyzing the color gamut of each frame of a video. At the recent Society for Information Display conference in Long Beach, CA, Clairvoyante demonstrated that this chip can analyze the colors in a given frame of video. In the next frame, it is able to make an adjustment to the panel backlight that maintains colors so that they look like traditional red-green-blue displays, says Pollack, while avoiding the constant use of maximum-intensity backlight. “Typically, we’re seeing movies with 40 to 50 percent power savings,” he says.

“I think it’s very interesting technology,” says Thrasyvoulos Pappas, professor of electrical engineering and computer science at Northwestern University, in Evanston, IL. Over the past couple of years, Pappas has seen growing research interest in red-green-blue-white displays. “The white [pixel] gives you more flexibility,” he says. “The more flexibility you have, the more options you have to maximize performance.”

Pollack says that later this year, Clairvoyante will release software so that developers can put PenTile dynamic backlight technology into products.

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