This image, from a Panasonic paper at the ISSCC computer-chip show, shows a sensor with a better ability to span bright and dark areas in a photo. It works by combining three shots into a single high-dynamic range image using a new Panasonic image sensor.
(Credit: Panasonic)SAN FRANCISCO-- Panasonic showed technology on Monday that could shift the digital photography trend of high-dynamic range photos off the computer and directly into a camera image sensor.
And it works through a variation of a familiar photographic technique called exposure bracketing. For years, photographers challenged by tough lighting conditions have taken multiple pictures of the same scene at different brightness levels--bracketing--to help ensure one photo has a good balance shadow and highlight details.
More recently, with the advent of computers, these bracketed exposures can be combined into a single high-dynamic range (HDR) image that captures both bright and dark areas--for example both the subtle tones of both a bride's white wedding dress and a groom's tuxedo--that lie beyond the abilities of the camera taking a single shot.
In research shown here at the International Solid-State Circuits Conference, Tokayoshi Yamada of Matsushita Electric Industrial--better known as Panasonic to most people--showed technology that he said lets an image sensor capture that high-dynamic range information.
With today's sensors, "You can get either highlight or shadow detail, depending on the exposure time. To get much wider dynamic range images, we need to combine these different-exposure images," Yamada said.
Yamada showed a 177x144 pixel image sensor that takes three photos of the same scene in rapid succession. In one example, he said, the first exposure lasts 1.5 microseconds, the second 150 microseconds, and the third 15,000 microseconds (not far from a 1/60 second exposure). Extra circuitry built into the sensor records the data from the multiple exposures and uses an assortment of electronic capacitors to combine it into a single image that spans a greater dynamic range.
The image can span a dynamic range of 140 decibels compared with ordinary sensors with a 60dB range when working at a frame rate of 15 frames per second, the researchers said.
In his presentation, Yamada showed a resulting image taken of a regular incandescent light bulb. With conventional sensor technology, a few of the words printed on the bulb were visible, but most were washed out in a blown-out white patch near the bulb's filament. In the Panasonic sensor's image, not only were most of the words visible, but also the helical coil of the filament was.
Combining multiple exposures has been possible before, but only using technology that recorded the multiple exposures in separate areas called frame memories, Yamada and his Panasonic colleagues said in a paper on the subject.
Despite efforts such as Fujifilm's SuperCCD sensors, camera buffs are often frustrated by the image sensor dynamic range of that's significantly weaker than what the human eye can detect. Although the Panasonic research shows some promise, though, photo nerds should rein in their hopes: the research showed only a black-and-white images so far and is suited "for automotive and security cameras," according to the researchers' paper.
Kodak says its new 5-megapixel sensor will fit in the small camera packages of mainstream mobile phones.
(Credit: Kodak)Eastman Kodak hopes turning one aspect of chip design on its head will help improve cell phone cameras--or at least help their image quality catch up with their megapixel increases.
"We believe we've created a new camera sensor product that rivals that of real cameras, but it's small enough to be used in a camera phone," said Fas Mosleh, manager of CMOS market work for Kodak's professional and applied imaging group.
There have been nice cameras in high-end mobile phones such as Nokia's N95, but Kodak believes its technology, built into a 5-megapixel sensor product to ship by the end of the year, will help bring better cameras to mainstream mobile phones.
Semiconductor chips currently detect light essentially by counting how many electrons result from light striking a pixel on the image sensor. More intense light means more electrons, and that electronic signal can be converted into digital data.
But Kodak believes it can get some improvements by rewiring the image sensor design to detect the absence of electrons instead--in effect counting "holes" rather than electrons. To do so, some sensor circuitry must be rewired, but Kodak argues that the technology produces less noise than conventional sensors.
The upshot, as promised by Kodak: better picture quality, or the same picture quality when shooting in dim light conditions such as those that prevail in most indoor scenes.
A basic problem with image sensors is the challenge of distinguishing the light's signal--the actual photons striking the sensor--from electronic noise within the sensor. That problem gets worse as pixels get smaller, so more megapixels isn't necessarily progress.
"Image quality has been deteriorating because your image resolution has been going up. Pixelization is better, but your low-light performance is worse," Mosleh said. "If you pick up a camera phone from 2003 or 2004 and compare to one from 2008, that old one will produce nicer pictures."
For product purposes, Kodak is pairing the hole-detector technology with a new color filter array Kodak calls Clear Pixel that's designed to improve low-light performance even more by devoting some pixels to measuring just brightness instead of color.
The 5-megapixel technology package, called the KAC05020, will fit into a small package measuring about .25 inch square and costing between $3 and $6 in large quantities, depending on what associated technology and software is included, Kodak said. It will support capture of 720p high-definition video, too.
Kodak researchers are presenting the sensor technology at the International Solid-State Circuits Conference on Monday in San Francisco.
The hole-detector pMOS technology could apply to larger sensors, but its benefits are clearer on small sensors, Mosleh said.
Kodak will offer KAC05020 samples in the second quarter, with high-volume shipments in the fourth quarter, the company said.
The hole detection, called pMOS in contrast to the usual NMOS sensors, can be built with no changes to semiconductor manufacturing, Mosleh said. However, some changes are necessary. "Pixel designers who have been working with collecting electrons now are collecting the absence. And the circuits coming off the sensor need to be repositioned, so support electronics need to be changed," he said.
Kodak's Clear Pixel technology, a variation on the Bayer pattern color filter array the company invented decades ago and now almost universal in digital cameras, is designed to improve sensitivity by devoting more pixels to detecting light intensity rather than color.
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