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LCD panel adapts itself to different viewing angles

06 Sep 2007

Taiwanese researchers have developed a new system that allows images on an LCD screen to look the same when viewed from any angle.

One of the biggest drawbacks of LCD displays is their limited viewing angle: images that look great when viewed from the front of the screen appear washed out and distorted when seen from the side. Now, however, Wayne Cheng and colleagues at the National Chiao Tung University in Taiwan, China, have developed a computerized display panel that tracks the position of the viewer and tailors the display's settings to ensure that the user gets the best view from any direction.

"Designers of cameras and cell phones assume that the user will look at the screen straight on, but this is not always the case," Cheng told optics.org. "We studied usage patterns and found that users often look at the screen from odd angles, and what they see is a distorted and blurry version of the actual image. Our goal was to devise a system that tracks the viewer and adjusts itself to provide the best image."

The limited viewing angle of LCDs is an inherent problem that arises from the way that they operate. LCD displays typically exploit a white backlight in conjunction with a panel of electrically activated crystals that behave like a grid of filters. When the screen is viewed from an angle, white light intended for one pixel "leaks" into an adjacent one, causing the images to look washed out and distorted. As a result, the contrast ratio can drop by more than a factor of 20 when the user gazes at the screen from the side.

The researchers addressed this problem by making some interesting hardware modifications to a standard 19 inch monitor. "We corrected the colour shift induced by light leakage by carefully characterizing the LCD controller and compensating for the normal viewing angle. And we replaced the white cold cathode fluorescent lamp backlights with RGB LED chips. Each chip had one red, one blue and two green LEDs."

A small camera placed next to the screen tracked the direction of the user's head and fed this information to the control module, which then adjusted the power input of the backlights and the orientation of the crystals. "To reduce the processing load, we got the user to wear a tiny infrared light source, which was tracked by a simple camera," said Cheng.

When the user is looking at the screen head on, the display is left at its original setting. But as he moves to the side, the backlights are adjusted to maintain the contrast ratio.

"Our system does not solve the viewing angle problem in LCDs, but finds a way to overcome it in certain scenarios." Suitable applications would be in mobile phones and cameras, where there is likely to be only one user at a time. The team is now focussing on extending the baseline system so that it can work well for multiple users."

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