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The Foveon X3 Sensor

The Foveon X3 Sensor

The Foveon sensor is structurally different from the conventional sensors used in cameras more common, based on the matrix Bayer (existing version is a CCD CMOS).

In Foveon sensor is employed an array of photosites, each of which is constituted by three photodiodes stacked vertically and arranged in a two-dimensional grid  akusaraprosound. Each of the three stacked photodiodes responds to different wavelengths of light ie each has a different spectral sensitivity curve (this difference is related to the fact that different wavelengths of light penetrate silicon to different depths). The signals of the three photodiodes are then processed so that each photodiode provides the value corresponding to one of three primary colors (red, green and blue).

In the illustration above shows the parallel between the sensor Foveon X3 (right) and the sensor based on the Bayer matrix (in the center). To the left, finally, it shows the schematization of how a color film captures the three primary colors: the sensor Foveon X3 wants, in practice, to imitate what is realized in the analog film.

The operation of the sensor Foveon X3 is very different from that of the sensor based on the Bayer filter. In the Bayer sensor, each photosite in the array consists of a single light sensor (CMOS or CCD) which, following filtration, is exposed to only one of the three primary colors (red, green or blue). For the realization of the final image captured by the sensor Bayer it is necessary to perform the demosaic, an interpolative process in which each pixel associated with each photosite is assigned an RGB value based on the combination of the values ??of red, green and blue photosites adjacent to it . On the contrary, the sensor Foveon X3 creates the yield of the RGB color for each photosite combining the outputs of each of the photodiodes stacked in each of its photosites. This operational difference has several consequences, not all positive (from which the poor diffusion).

Color artifacts

Because in the case of the Foveon X3 is not expected to demosaicing to produce a color image, color artifacts associated with this process are not present. The anti-aliasing filter typical sensor Bayer to limit these artifacts is not present. This enables a higher quality image. On the contrary, however, the method of color separation linked to the penetration depth of the silicon creates problems in the “color accuracy”, in particular with the red channel. The photo is then less true from the point of view of color.

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