Nikon patents full-color RGB sensor
By
Mike Tomkins
(Thursday, August 9, 2007 - 17:14 EDT)
Our friends over at the Digital Photography Review website have picked up on an interest patent from Japan's Nikon Corp.
A Canadian photographer and DPReview member found the patent, which is entitled "Color Separation Device of Solid-State Image Sensor", and posted mention of it in the site's forum. First filed in December 2003, the document is based on a Japanese patent that Nikon had filed almost exactly a year earlier and which was in turn granted in mid-July 2004.
If you read Japanese, you can browse that document - number JP2004200358 - through the website of European Patent Organisation. Note that the assignee name on the patent, Nippon Kogaku K.K., is the original name of what later became known as Nikon Corp. The followup US patent - number 7,138,663 - was eventually granted in late November of 2006 and can also be read in full online courtesy of the United States Patent and Trademark Office.
Both patents cover a system for determining full RGB color information at every pixel location on a single image sensor. This feat has been achieved in the past by Foveon Inc., whose X3 image sensors use red, green and blue photodiodes that are stacked vertically on top of each other. Nikon's patent uses a rather different approach, however. The photodiodes measuring red, green and blue light for one specific pixel location are placed side by side below a microlens that focuses that pixel's light into a row of several dichroic mirrors, one above each photodiode.
At the first dichroic mirror, blue light is passed through into the photodiode below, while red and green light are reflected towards the next mirror. The second mirror reflects the green light towards the second photodiode, while allowing the red light to continue onwards where it strikes the third and final mirror. There, it is reflected downwards onto the third and final photodiode.
Definitely an interesting system, but it remains to be seen whether Nikon intends to commercialize any product based on the concept. If so, it could prove a major rival to Foveon's X3 imager, which has so far only appeared in Sigma's SLR cameras and a single Polaroid point-and-shoot (excluding industrial usage). Complexity of the design is perhaps the main potential pitfall that could prevent products based on the new technology seeing the light of day.
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