Color filter array

In photography, a color filter array (CFA), or color filter mosaic (CFM), is a mosaic of tiny color filters placed over the pixel sensors of an image sensor to capture color information. In photography, a color filter array (CFA), or color filter mosaic (CFM), is a mosaic of tiny color filters placed over the pixel sensors of an image sensor to capture color information. Color filters are needed because the typical photosensors detect light intensity with little or no wavelength specificity, and therefore cannot separate color information.Since sensors are made of semiconductors they obey solid-state physics. The color filters filter the light by wavelength range, such that the separate filtered intensities include information about the color of light.For example, the Bayer filter (shown to the right) gives information about the intensity of light in red, green, and blue (RGB) wavelength regions. The raw image data captured by the image sensor is then converted to a full-color image (with intensities of all three primary colors represented at each pixel) by a demosaicing algorithm which is tailored for each type of color filter.The spectral transmittance of the CFA elements along with the demosaicing algorithm jointly determine the color rendition. The sensor's passband quantum efficiency and span of the CFA's spectral responses are typically wider than the visible spectrum, thus all visible colors can be distinguished. The responses of the filters do not generally correspond to the CIE color matching functions, so a color translation is required to convert the tristimulus values into a common, absolute color space. The Foveon X3 sensor uses a different structure such that a pixel utilizes properties of multi-junctions to stack blue, green, and red sensors on top of each other. This arrangement does not require a demosaicing algorithm because each pixel has information about each color. Dick Merrill of Foveon distinguishes the approaches as 'vertical color filter' for the Foveon X3 versus 'lateral color filter' for the CFA. An RGBW matrix (from red, green, blue, white) is a CFA that includes 'white' or transparent filter elements that allow the photodiode to respond to all colors of light; that is, some cells are 'panchromatic', and more of the light is detected, rather than absorbed, compared to the Bayer matrix. Sugiyama filed for a patent on such an arrangement in 2005. Kodak announced several RGBW CFA patents in 2007, all of which have the property that when the panchromatic cells are ignored, the remaining color filtered cells are arranged such that their data can be processed with a standard Bayer demosaicing algorithm. A CYGM matrix (cyan, yellow, green, magenta) is a CFA that uses mostly secondary colors, again to allow more of the incident light to be detected rather than absorbed. Other variants include CMY and CMYW matrices. Diazonaphthoquinone (DNQ)-novolac photoresist is one material used as the carrier for making color filters from color dyes. There is some interference between the dyes and the ultraviolet light needed to properly expose the polymer, though solutions have been found for this problem. Color photoresists sometimes used include those with chemical monikers CMCR101R, CMCR101G, CMCR101B, CMCR106R, CMCR106G, and CMCR106B. A few sources discuss other specific chemical substances, attending optical properties, and optimal manufacturing processes of color filter arrays. For instance, Nakamura said that materials for on-chip color filter arrays fall into two categories: pigment and dye. Pigment based CFAs have become the dominant option because they offer higher heat resistance and light resistance compared to dye based CFAs. In either case, thicknesses ranging up to 1 micrometre are readily available.