![]() The Canon EOS-1D had 4.2MPx and the Nikon D100 had 6MPx. On paper, at least, removing any color filter should increase the light flux falling on the sensor and remove the drawbacks associated with color filters.īack when Foveon sensors first reached the market in 2002 in the Sigma SD9 DSLR, most digital cameras were far from 10MPx resolution. Illustration by Anoneditor and licensed under CC BY-SA 3.0. Wavelength-dependent absorption in silicon and the Foveon X3 sensor. The clever idea of Foveon sensors is to use “depth filters” instead of side-by-side color filters. Since absorption depth in silicon provides an estimate of the photon wavelength, the measure of the absorption depth provides theoretically the color information. An absoption depth of, for example, 1 um means that the light intensity has fallen to 36% (1/e) of its original value.” Chart by Christiana Honsberg and Stuart Bowden of ASU. “The absorption depth is the inverse of the absorption coefficient. Short wavelength photons (blue light, UV light, etc.) are more energetic than longer wavelength ones (red light, infrared light, etc.) and thus are absorbed after a shorter journey in silicon. This “travel distance” is related to the energy of the photon, which depends on its wavelength. It happens that, depending on its color, a given photon travels a specific distance in silicon before being absorbed. The absorption varies depending on the filter choice and image content, but it is generally admitted that the light flux is divided by a factor of 3 before reaching the sensor. Many interpolation algorithms exist, but the process always results in some form of color artifact and image softening.Ĭolor filter arrays, in addition to being inaccurate, also absorb many photons in the process of collecting some color information. For a given “red” pixel, one has to make an interpolation to find the missing green and blue information. However, the process comes at the expense of some image resolution. Thanks to these three filters, one can recover the color information in the image. Illustration by Cburnett and licensed under CC BY-SA 3.0. A profile view of a Bayer filter on an image sensor. Usually, this filter is organized following a Bayer pattern (from the name of a Kodak engineer) with red, green, green, and blue filters. From there on, the most common way to gather some color information is to use a color filter array (CFA).
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