Foveon X3 sensor
The manufactured by Foveon Foveon X3 CMOS sensor used instead of several adjacent layers 3 superimposed sensor elements to be recorded at each pixel of all three primary colors.
Principle of operation
The different wavelengths of red, green and blue are absorbed in different layers, because long-wavelength (red ) light in silicon has a greater penetration depth than short-wavelength (blue ). When using an infrared cut filter are obtained for the layers of the sensor color sensitivities are similar to the sensitivities of the cones of the human eye. The multi- layer principle is a similar application in color photography with color films in which also several color-sensitive layers are superimposed.
Comparison with conventional color digital cameras
In conventional sensors with Bayer mosaic color filters occurs - especially noticeable with fine patterns, - in red and blue, but also in green to beats and color edges by sampling error. Only 25% (or 50 % in green ) of their sensor area each receive a primary color. Between the individual color pixels remain touchlacks. Also point light sources at a greater distance could be for example "overlooked" or recorded incorrectly colored.
The classic color fringes or "artifacts" in raising Bayer sensor images do not occur in Foveon sensor. Thus, in comparison can not initially be brought quite as sharp acting Foveon images later on a high level. Compared with the Bayer sensor, the resolution is about two thirds of the manufacturer. A 14 megapixels ( effective 3 × 4.7 MP) resolution offered Foveon camera corresponds to a Bayer camera with 10.5 megapixels (monochrome - 5.25 MP effective green and 2.625 per MP red and blue - on the arithmetic average 3 5 MP).
When Foveon X3 sensor, no interpolation is necessary as for sensors with Bayer mosaic color filter. Each individual sensor pixels absorbs all color information. For example, for generating high quality color images, such as for metrological applications, arising from systematic advantages.
Another not always purported to withdraw the benefit of the Foveon X3 sensor is supposed to be a high color fidelity. In practice, it turns out that the color purity is at times over-emphasized elsewhere reduced contrast. Grey Blue and Purple are to bright gentian blue, leaf green tones are poorly differentiated and sometimes tend in the direction of a yellowish Olivs.
The disadvantage is a colored noise may be noticeable, which differs mainly by its eye-catching, usually green or yellow grittiness from the neutral color noise at Bayer sensors. Low brightness is synonymous with low photon radiation, which generally leads to a photo-sensor to a weak signal. Weak signals need to be processed can be enhanced in certain circumstances. In low signal gains, it is much more difficult to ensure the proportionality between input and desired signal for digitizing.
When Foveon sensor three layers are now to penetrate. Inevitably, the photon beam be filtered from layer to layer is weaker. The filter effect of the layers is based on the physical properties of the layer material. It inevitably has a bandwidth filtered out light frequencies. The noise of the three layers is thus not identical. Now that the three layers are responsible for each color, there may be noise on the different respective colors, especially in color, which is assigned to the lowermost layer. Therefore, the under-exposure noise always sets in a red color.
Sigma is for the Foveon X3 " direct image sensor " of resolutions that arise despite the staggering depth of the three colors at a pixel resolution in analogy to information for Bayer sensors out of three times the number of pixels.
The resolution of cameras with a Bayer sensor and the same number of pixels is in fact not been reached in relation to the luminance. However, the Foveon X3 in the color resolution is clearly superior to the image sensors with color mosaics. The optical resolution that will actually be achieved with a camera is often limited by the image resolution, but by other factors, such as the use of optical low-pass filtering and noise reduction methods, or by aberrations and focusing errors.
Currently the chip is installed only by Sigma in the digital SLR SD9, SD10, SD14, SD15 and the SD1 new professional camera with 46 MP and the compact cameras DP1, DP2 and DP3 series. In 2004 with the Polaroid X530 chip was also used, the X530 never reached because of their problems with in-camera image processing, however, the market and has been withdrawn in the introduction phase.