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The '''Foveon X3 sensor'''
[[As of 2005]], the Foveon X3 sensor is only used in the [[Sigma Corporation|Sigma]] SD9 and SD10 digital SLR cameras and the [[Polaroid Corporation|Polaroid]] x530 compact digital camera.
The Foveon X3 sensor is difficult to classify by [[megapixel]] count compared to mosaic sensor cameras, in which the photosite count and sensor count are the same. The Foveon X3, on the other hand, has three times the number of sensors than photosites, since each photosite has sensors for all three primary colors. Comparing sensors by number of photosites underestimates the resolution of the Foveon X3 sensor, since no de-mosiacing interpolation is required to achieve full color information at each site. On the other hand, comparison by sensor count over-states the resolution in comparison to a Bayer sensor. Independent comparisons of quality tend to rate the Foveon X3 sensor as equivalent to a Bayer sensor of double the photosite count.
One advantage of the Foveon sensor over the more conventional mosaic sensors, such as the [[Bayer sensor]], is that the captured image does not require [[anti-aliasing]] to remove the "coloured jaggies" characteristic to an unprocessed mosaic sensor image. This anti-aliasing step is the cause of the soft appearance of images captured with a digital camera, and the cause for most digital cameras to apply a sharpening filter to an image automatically, to add the illusion of sharpness.
Another Foveon advantage is that each pixel can potentially detect more photons, also improving sharpness. Each pixel of a mosaic sensor is covered by a light filter that passes only one of the primary colors, absorbing the other two. Absorbing the light destroys information about that pixel, making the image fuzzier and grainier. This advantage is largely overcome by the math required to reconstruct color information from the Foveon sensor, which results in a Foveon sensor with very large photosites often being unable to equal the low light performance of more
As a rough rule of thumb, an image captured with a Foveon sensor will in theory contain about as much detail as a [[Bayer sensor]] with twice as many photosites. For example, a 3 megapixel Foveon sensor and a 6 megapixel Bayer sensor should be roughly equal in measurable detail. This could be considered a major disadantage of the Foveon sensor, as the afore mentioned 3 megapixel Foveon sensor will produce 50% more data (which needs to be processed and stored) as a 6 megapixel Bayer sensor.
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The question of whether to count each stack of three photosensors as a pixel, versus counting each individual single-color photosensor as a pixel as is done in Bayer-mosaic sensors, has been a point of controvery for Foveon X3 sensors and for the specifications of cameras that use them. For example, the camera Sigma SD10, which produces a native RAW file size of 3.4 Million RGB pixels, is advertised as a 10.2 MP camera, sometimes with the clarification "3.4 MP Red + 3.4 MP Green + 3.4 MP Blue"; an 8 MP Bayer-mosaic camera would similarly be clarified to be 2 MP Red + 4 MP Green + 2 MP Blue. The word "photosite" is also used in both senses (even in the opening paragraph of this article!).
==External links==
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