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Friday, March 29, 2013

Panasonic Filters Improve Low Light Performance

Panasonic has developed a unique technology that doubles the brightness of color photography, by using micro color splitters instead of conventional color filters in the image sensor. What makes this technology interesting is the camera's sensor does not need to be modified in any way and the material and manufacturing techniques required to make the new filters are the same ones in use today already. This means if Panasonic decides to put this invention into production, it can come to the market soon. You can view the video on YouTube to get more information.

The two photos above were taken using CCDs with the same sensitivity. The one on the right was taken with the color filter system used in nearly all digital cameras. The one on the left was taken with Panasonic's new micro color-splitting system.

Until now, image sensors have produced color pictures by using red, green, and blue filters for each pixel, but with that system, 50-70% of the light is lost.

"Here, color filters are not used. So light can be captured without loss, which enables us to achieve approximately double the sensitivity. In addition, this technology can be used regardless of whether the sensor is a CCD, CMOS, or BSI type. The device can also be manufactured using current semiconductor fabrication processes. It does not use special materials or processes."

This photo shows a cross section of the the new image sensor. The sensor uses two types of color splitters : red deflectors and blue deflectors.

The red and blue deflectors are arranged diagonally, with one of each for every four pixels. RGB values can be obtained by determining the intensity of light reaching each of the four pixels.

For example, if white light enters each pixel, pixels where it doesn't pass through a deflector receive unmodified white light. But in pixels with a red deflector, the light is split into red diffracted light and cyan non-diffracted light. And when white light passes through a blue deflector, it's split into blue diffracted light and yellow non-diffracted light. As a result, the pixel arrangement is cyan, white + red, white + blue, and yellow. The RGB values are then calculated using a processing technique designed specifically for mixed color signals.

To design the micro color splitters in this way, it is necessary to analyze optical phenomena such as reflection, refraction, and diffraction, in 3D. Analyzing various wavelengths of light for each form of micro color splitter requires high-speed computation, which hasn't been practical until now.

The design of these micro color splitters was achieved by using a new wave-optics analysis technology, which makes it possible to calculate reflection, refraction, and diffraction quickly and accurately.

"We have developed a completely new analysis method, called Babinet-BPM. Compared with the usual FDTD method, the computation speed is 325 times higher, but it only consumes 1/16 of the memory. This is the result of a three-hour calculation by the FDTD method. We achieved the same result in just 36.9 seconds."

"Here, we've used a two-deflector method. But various combinations are possible. For example, you could increase the S/N ratio by using four deflectors. You could use one combination for mobile applications, and another for security cameras. From now on, we'd like to shift the focus of our research to different systems for different applications."

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