The most common way we get color images with digital cameras is with a Bayer pattern CMOS sensor, but there are plenty of variations on that design being used today. The upcoming Aaton Penelope Delta uses a Bayer pattern over a Dalsa CCD, for example, while the RED EPIC-M Monochrome uses the MX CMOS sensor foregoing color filtration entirely. By their very nature, though, color filters of any kind cut down the amount of light transmitted to the sensor. That's why Panasonic is developing a brand new type of color filter that will employ diffraction to split up the color spectrum, instead of filtration, and thus will be capable of doubling the light sensitivity of the sensor.
Panasonic's Sensor Filters By Way of 'Micro' Diffraction
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.
The developed technology has the following features.
- Using color alignment, which can use light more efficiently, instead of color filters, vivid color photographs can be taken at half the light levels needed by conventional sensors.
- Micro color splitters can simply replace the color filters in conventional image sensors, and are not dependent on the type of image sensor (CCD or CMOS) underneath.
- Micro color splitters can be fabricated using inorganic materials and existing semiconductor fabrication processes.
Followed by a bit more on how all this works:
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.
They seem to be saying in their materials that there is no loss of resolution due to using this method. This would be in contrast to a traditional Bayer pattern filter which loses some resolution thanks to interpolation, since not every color is represented on every pixel (unlike your 3-CMOS or 3-CCD cameras). In practice it may not be perfect, but this development is definitely exciting, as it looks like it will improve sensor performance without needing to completely redesign the sensor or the manufacturing process. Developments like this are important as sensors reach their physical limit of light sensitivity and color reproduction at given sizes -- like the Super 35mm/APS-C size, which RED is certainly pushing to its limits with their new Dragon sensor.
Some Background Material
Some additional context may be useful when considering the 'Highly Sensitive Image Sensors Using Micro Color Splitters' featured in Panasonic's announcement. Panasonic's new sensor technology is by no means the first to deviate from the Bayer pattern standard (which our own Joe Marine explains here). It is also not the first to achieve full-color reproduction without a Bayer pattern, either:
Other Unique Sensor Designs
- The Sigma/Foveon X3 sensor actually uses three stacked photodiode layers so that each pixel has its own complete RGB information (pictured right, courtesy Sigma). This is possible due to something called 'wavelength-dependent absorption depth' [PDF] meaning each layer only absorbs part of the spectrum. Used in the SD1 Merrill and other Sigma stills camera models.
- Sony's CineAlta F35 HD digital cinema camera uses a CCD with a very unique color filter array. Instead of the bayer 'RGBGxGBGR' pattern, the F35's 5760x2160 sensor is arranged in a 'RGBxRGB' pattern that averages rectangular blocks of 6 (every 3 horiz. x 2 vert.) sensor pixels into each final pixel of the 1920x1080 image. This gives the F35 powerful color fidelity and SNR [via PVC's Art Adams].
- The Aaton Penelope Delta uses an ISO 800 Dalsa CCD that will actually have the ability to physically oscillate in place by 1/2 pixel each frame. This 'time traveling' sensor theoretically increases its 3.5K RAW yield to 7K RAW by this action, due to alleviation of the fixed noise structure inherent to any image sensor.
- Lytro and plenoptic/light field photography are not yet fully developed technologies, but in terms of unique sensors they at least deserve an honorable mention. Lytro technology allows for refocusing and perspective shift after the photo is taken because its micro-lens array gathers light from different directions simultaneously.
For more general reading material on imager comparison, you can check out Dalsa's article on CMOS vs. CCD sensors.
What do you guys think?