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Panasonic has devised a method to increase the sensitivity of image sensors, by replacing the near-universal colour filter array with prism-like 'Micro Color Splitters' to generate colour information. The key advantage is that all of the incoming light is directed to the sensor, instead of half or more being absorbed by the colour filter dyes. This promises to deliver images with less noise in low light. The development is published in the journal Nature Photonics, and outlined in a press release on Panasonic's website.
According to Panasonic, the dyes used in conventional colour filter arrays absorb at least half of the incoming light before it reaches the sensor's photosites. In contrast, the company's 'Micro Color Splitter' technology passes all of the incoming light to the sensor. In practical terms, this corresponds to a sensitivity increase of a whole stop, which should in turn result in a stop improvement in noise performance. In other words, a 'Micro Color Splitter'-based sensor should give similar noise at ISO 3200 as a conventional Bayer sensor does at ISO 1600, for example.
Perhaps the most interesting aspect of this development is that it may be the first serious alternative to colour filter array-based sensors since the Foveon X3 appeared over 10 years ago. Like any new technology there'll be plenty of development to do before it appears in a real product, but the prospect of a stop better high ISO performance is certainly a tantalising one.
|Constitution and features compared with the conventional method|
Osaka, Japan - Panasonic Corporation has developed unique "micro color splitters", which separate the light that falls on image sensors by exploiting light's wavelike properties. Applying them to actual image sensors allows bright color images to be achieved even under low-light conditions. This development makes color filters unnecessary by using the micro color splitters that control the diffraction of light at a microscopic level. Panasonic has achieved approximately double the color sensitivity in comparison with conventional sensors that use color filters.
Image sensors are used in devices like smartphones, digital still cameras and video cameras, as well in security, vehicle parking, office, and healthcare applications - anywhere, in fact, that digital imaging is needed. Conventional color image sensors use a Bayer array, in which a red, green, or blue light-transmitting filter is placed above each sensor. These filters block 50 - 70% of the incoming light before it even reaches the sensor. Progress is being made in increasing the resolution of image sensors used in mobile and other devices by reducing pixel size, but demand for higher-sensitivity cameras is also increasing. Panasonic has developed a new technology that can be applied to existing or future sensors to enable them to capture uniquely vivid color images.
The developed technology has the following features.
This development is based on the following new technology.
Panasonic holds 21 Japanese patents and 16 overseas patents, including pending applications, for this development.
This development is described in general terms in the Advance Online Publication version of Nature Photonics issued on February 3, 2013.
|Conventional method using a color filter||Developed method using a micro color splitter|
FDTD is widely used to analyze light in wave form, but its heavy computation workload has up to now made it impractical for designing micro color splitters. On the other hand, BPM is an effective method of fast computation, but it has lower precision than FDTD and cannot accurately simulate color splitting. This prompted Panasonic to develop a practical and original design method that permits fast and precise computation of wave-optics phenomena. This technology allows the precise modeling of optical phenomena such as reflection, refraction, and diffraction by modeling spaces in regions with different optical constants and applying BPM to the spaces. This method can be applied not only to the design of micro color splitters, but can be extended to the design of other nano-scale optical processing systems.
Color separation of light in micro color splitters is caused by a difference in refractive index between a) the plate-like high refractive material that is thinner than the wavelength of the light and b) the surrounding material. Controlling the phase of traveling light by optimizing the shape parameters causes diffraction phenomena that are seen only on a microscopic scale and which cause color separation. Micro color splitters are fabricated using a conventional semiconductor manufacturing process. Fine-tuning their shapes causes the efficient separation of certain colors and their complementary colors, or the splitting of white light into blue, green, and red like a prism, with almost no loss of light.
Since light separated by micro color splitters falls on the detectors in an overlapping manner, a new pixel layout and design algorithm are needed. The layout scheme is combined and optimized using an arithmetic processing technique designed specifically for mixed color signals. The result is highly sensitive and precise color reproduction. For example, if the structure separates light into a certain color and its complementary color, color pixels of white + red, white - red, white + blue, and white - blue are obtained and, using the arithmetic processing technique, are translated into normal color images without any loss of resolution.