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Foveon Inc. developed the X3 image sensor technology, incorporating a patented three-layer image sensor architecture. The technology, which uses standard CMOS semiconductor process, is first commercial image sensor that does not require color filters to create a color image. Foveon X3 image sensors have three colour layers of pixels (blue, green and red), which are analagous to the layers of chemical emulsion used in color film.
The Foveon X3 technology has some technical advantages over Charged Couple Device (CCD) image sensors. CCDs use a Bayer filter mosaic where sensor elements of individual colours are arranged in a pattern. The problem is that no one sensor element location can sense more than one colour, so these are generally arranged under a layer of microlenses and the colour at each sensor site is interpolated. Furthermore, this method can give to Moiré patterns, particularly with red diagonal stripes, so an anti-aliasing blur filter is placed over the sensor. The anti-aliasing filter also reduces detail visible in the image generated. As the Foveon X3 technology requires no Bayer pattern to produce true three channel colour at each sensor element site, images produced can be seen to have more colour definition and more subtle tonal qualities. As the technology has much less tendency to produce aliasing effects, no anti-aliasing filteris required and details are not lost. Furthermore, as each sensor element site is arranged in a stack of three colours, the Foveon X3 sensor element pitch can be wider and less susceptible to diffraction limitations on resolution.
As camera manufacturers with Bayer-pattern sensors claim each colour of each sensor element as one pixel, Foveon claims the same. Some Sigma digital cameras have the option of re-interpreting sensor data to interpolate detail as a Bayer sensor would interpolate colour. Foveon's calculation not uncontroversial and some consider this to be overstating sensor resolution by a factor of three. In reality, both calculations have merit and neither are directly comparable; it is a different technology with different characteristics. Foveon Inc. was purchased by Sigma in November 2008, but Foveon continues to be based in San Jose, CA, USA.