Display brighter than film
By
Kimberly Patch,
Technology Research NewsThe human eye is capable of seeing the whole range of brightness the sun's proximity brings to the earth -- nearly seven orders of magnitude, or 10 million to 1. The contrast between a bright sunny day and a moonless night, for example, is around a million to one.
Today's computer screens, however, display only a fraction of that range. The liquid crystal screens used in laptops, palmtops and cell phones average around 300 to 1, and top out at 800 to 1. Turn up the brightness of a liquid crystal display and the whole range changes -- the black becomes less intense as other colors brighten.
Researchers from York University in Canada, the University of British Columbia in Canada, and Sunnybrook Technologies Inc. have devised a way to boost the dynamic range of liquid crystal displays to 90,000 to 1.
The technology promises to bring a more realistic brightness range to any type of computer screen, which will make for better and more informative pictures, according to Helge Seetzen, director of the Emissive Display program at Sunnybrook Technologies.
The human visual system has evolved to see the high dynamic range found in the world, said Seetzen. Many aspects of our perception are based on that evolution, including attention, aesthetics, 3D perception and emotions, he said.
A key application is improving the ability to view medical imaging data, Seetzen said. Like movie film, medical imaging data has a dynamic range as high as 8,000 to 1. But because of the limitations of today's computer displays, data is often broken up into many pictures that show a series of brightness ranges. In order to avoid this problem, x-ray film is often still shown on light boxes.
The display could also improve architectural rendering, including lighting simulations, flight and vehicle simulators, and military command and control viewers, said Seetzen.
In general, the system can display more life-like images, said Wolfgang Stuerzlinger an associate professor of computer science at York University. "Highlights on shiny objects look... more realistic, which in turn enhances the perception of the shape of the objects," he said. The display can also generate much darker intensities than conventional monitors, he said.
The trick to increasing the brightness of a liquid crystal display is dividing the backlight into segments, and controlling those segments separately. A backlight shines through the pixels to provide most of the brightness of a screen. A conventional liquid crystal display is backlit uniformly and each pixel is adjusted to gain a brightness range.
The researchers' high dynamic range display technology uses a matrix of high brightness light-emitting diodes (LEDs) as a backlight. "Where the final image is very bright we increase the brightness of the LEDs and in the dark region the LEDs are very dim," said Seetzen.
Having the layer of light-emitting diodes behind the liquid crystal display makes the brightness range 300 times 300 to one, or 90,000 to one, he said. "This high contrast... allows us to use very bright LEDs without losing the perfect black of the displays," he said.
The key to making the scheme work was controlling the blur caused by the size mismatch between the light-emitting diode backlights and the liquid crystal pixels, said Seetzen. The researchers compensated for most of the blur using software. The remaining blur, at very high-contrast boundaries at the top of a single light-emitting diode, is imperceptible to the human eye, he said. The blur is hidden by an effect similar to the halos seen around streetlights at night. "The halo goes away if you mask the light source with your thumb even though the thumb doesn't mask the halo area," said Seetzen.
The displays consume about as much power as conventional displays, said Seetzen. "This sounds surprising, but is the result of controlled creation of light," he said. "Most areas in the average images aren't at the top brightness end -- or we would have a desire for sunglasses all the time -- so the vast majority of the LEDs are actually providing fairly little light at a given time and thus consume very little power."
Because the researchers' display uses hundreds of light-emitting diodes as a backlight rather than a pair of fluorescent tubes, it is potentially more expensive than current displays, said Seetzen. "For a 20 inch medical LCD the added costs will probably be around $500 or so," he said.
Prices for light-emitting diodes are decreasing by a factor of two every couple of months, however, said Seetzen. It is likely to take another two to three years of price decreases to make the screens cost-competitive for consumer products like televisions, he said.
The display is compatible with standard graphics cards, and is built from commercially available parts, Seetzen added.
According to the researchers' studies, it is possible to further increase the LEDs size without decreasing the spatial resolution and crispness of the image, said Seetzen. "This will further reduce complexity and cost," he said.
Seetzen and Stürzlinger's research colleagues were Andrejs Vorozcovs and Hugh R. Wilson from York University and Ian Ashdown, Greg Ward and Lorne Whitehead from the University of British Columbia. The researchers presented the work at the Association of Computing Machinery (ACM) Special Interest Group Graphics (Siggraph) 2003 conference in San Diego, July 27 to 31. The work was funded by the Canadian Natural Science and Engineering Research Council and Sunnybrook Technologies.
Timeline: > 1 year
Funding: Corporate; Government
TRN Categories: Data Representation and Simulation; Graphics
Story Type: News
Related Elements: Presentation, "High-Dynamic-Range Display System," at the Association of Computing Machinery (ACM) Special Interest Group Graphics (Siggraph) 2003 conference in San Diego, July 27 to 31.
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September 10/17, 2003
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