A
Bayer filter mosaic is a
color filter arrayIn photography, a color filter array , or color filter mosaic , is a mosaic of tiny color filters placed over the pixel sensors of an image sensor to capture color information....
(CFA) for arranging
RGBThe RGB color model is an additive color model in which red, green, and blue light are added together in various ways to reproduce a broad array of colors...
color filters on a square grid of photosensors. Its particular arrangement of color filters is used in most single-chip digital
image sensorAn image sensor is a device that converts an optical image to an electric signal. It is used mostly in digital cameras and other imaging devices. An image sensor is typically a charge-coupled device or a complementary metal–oxide–semiconductor active-pixel sensor.- CCD vs CMOS :Today, most...
s used in digital cameras, camcorders, and scanners to create a color image. The filter pattern is 50% green, 25% red and 25% blue, hence is also called
GRGB or other permutation such as
RGGB.
It is named after its inventor,
Bryce E.
A
Bayer filter mosaic is a
color filter arrayIn photography, a color filter array , or color filter mosaic , is a mosaic of tiny color filters placed over the pixel sensors of an image sensor to capture color information....
(CFA) for arranging
RGBThe RGB color model is an additive color model in which red, green, and blue light are added together in various ways to reproduce a broad array of colors...
color filters on a square grid of photosensors. Its particular arrangement of color filters is used in most single-chip digital
image sensorAn image sensor is a device that converts an optical image to an electric signal. It is used mostly in digital cameras and other imaging devices. An image sensor is typically a charge-coupled device or a complementary metal–oxide–semiconductor active-pixel sensor.- CCD vs CMOS :Today, most...
s used in digital cameras, camcorders, and scanners to create a color image. The filter pattern is 50% green, 25% red and 25% blue, hence is also called
GRGB or other permutation such as
RGGB.
It is named after its inventor,
Bryce E. Bayer of
Eastman KodakEastman Kodak Company is a multinational US corporation which produces imaging and photographic materials and equipment. Long known for its wide range of photographic film products, Kodak is re-focusing on two major markets: digital photography and digital printing.- Origins :Kodak's origins rest...
. Bayer is also known for his recursively defined matrix used in
ordered ditheringOrdered dithering is an image dithering algorithm. It is commonly used by programs that need to provide continuous image of higher colors on a display of less color depth. For example, Microsoft Windows uses it in 16-color graphics modes...
.
Explanation
Bryce Bayer's patent (U.S. Patent No. 3,971,065) called the green photosensors
luminance-sensitive elements and the red and blue ones
chrominance-sensitive elements. He used twice as many green elements as red or blue to mimic the human eye's greater resolving power with green light. These elements are referred to as
sensor elements,
sensels,
pixel sensors, or simply
pixels; sample values sensed by them, after interpolation, become image pixels.
The
raw outputA camera raw image file contains minimally processed data from the image sensor of either a digital camera, image or motion picture film scanner. Raw files are so named because they are not yet processed and therefore are not ready to be used with a bitmap graphics editor or printed...
of Bayer-filter cameras is referred to as a
Bayer pattern image. Since each pixel is filtered to record only one of three colors, the data from each pixel cannot fully determine color on its own. To obtain a full-color image, various
demosaicingA demosaicing algorithm is a digital image process used to reconstruct a full color image from the incomplete color samples output from an image sensor overlaid with a color filter array...
algorithms can be used to
interpolateIn the mathematical subfield of numerical analysis, interpolation is a method of constructing new data points within the range of a discrete set of known data points....
a set of complete red, green, and blue values for each point.
Different algorithms requiring various amounts of computing power result in varying-quality final images. This can be done in-camera, producing a
JPEGIn computing, JPEG is a commonly used method of compression for photographic images. The degree of compression can be adjusted, allowing a selectable tradeoff between storage size and image quality...
or TIFF image, or outside the camera using the raw data directly from the sensor.
Alternatives
The Bayer filter is almost universal on consumer digital cameras. Alternatives include the
CYGM filterIn digital photography, the CYGM filter is an alternative color filter array to the Bayer filter . It similarly uses a mosaic of pixel filters, of cyan, yellow, green and magenta, and so also requires demosaicing to produce a full-colour image....
(cyan, yellow, green, magenta) and
RGBE filterIn digital photography, the RGBE filter is an alternative color filter array to the Bayer filter . It similarly uses a mosaic of pixel filters, of red, green, blue and "emerald" , and so also requires demosaicing to produce a full-color image...
(red, green, blue, emerald), which require similar demosaicing; the
Foveon X3 sensorThe Foveon X3 sensor is a CMOS image sensor for digital cameras, designed by Foveon, Inc. and manufactured by National Semiconductor and Dongbu Electronics. It uses an array of photosites, each of which consists of three vertically stacked photodiodes, that are organized in a two-dimensional grid...
, which layers red, green, and blue sensors vertically rather than using a mosaic; or using
three separate CCDsThree-CCD or 3CCD is a term used to describe an imaging system employed by some still cameras, video cameras, telecine and camcorders. Three-CCD cameras have three separate charge-coupled devices , each one taking a separate measurement of red, green, and blue light...
, one for each color, which is far more expensive.
"Panchromatic" cells
On June 14, 2007,
Eastman KodakEastman Kodak Company is a multinational US corporation which produces imaging and photographic materials and equipment. Long known for its wide range of photographic film products, Kodak is re-focusing on two major markets: digital photography and digital printing.- Origins :Kodak's origins rest...
announced an alternative to the Bayer filter: a color-filter pattern that increases the sensitivity to light of the image sensor in a digital camera by using some "panchromatic" cells that are sensitive to all wavelengths of visible light and collect a larger amount of light striking the sensor. They present several patterns, but none with a repeating unit as small as the Bayer pattern's 2×2 unit.
Another 2007 U.S. patent filing, by Edward T. Chang, claims a sensor where "the color filter has a pattern comprising 2×2 blocks of pixels composed of one red, one blue, one green and one transparent pixel," in a configuration intended to include infrared sensitivity for higher overall sensitivity. The Kodak patent filing was earlier.
Such cells have previously been used in "CMYW" (cyan, magenta, yellow, and white) "RGBW" (red, green, blue, white) sensors, but Kodak has not compared the new filter pattern to them yet.
Microlenses and dichroic mirrors
On November 21, 2006, Nikon Corporation was granted U.S. patent
7,138,663 which places a microlens over a triplet of photoreceptors. Specific wavelengths of light are separated and passed to specific photoreceptors designated to record red, green, and blue wavelengths. Light separation is achieved with
dichroic mirrorsA dichroic filter or thin-film filter is a very accurate color filter used to selectively pass light of a small range of colors while reflecting other colors. By comparison, dichroic mirrors and dichroic reflectors tend to be characterized by the color of light that they reflect, rather than the...
. This system emulates
three-CCDThree-CCD or 3CCD is a term used to describe an imaging system employed by some still cameras, video cameras, telecine and camcorders. Three-CCD cameras have three separate charge-coupled devices , each one taking a separate measurement of red, green, and blue light...
imaging systems with a single array. Image quality is theoretically improved due to much smaller gaps between photoreceptors assigned to a wavelength (each microlens lens acts as a collector for all pertinent wavelengths of light) and reduced light loss through the absence of wavelength filters.
Foveon's vertical color filter
Another type of color separation, sometimes called vertical color filter, as opposed to lateral color filter, is used in the
Foveon X3 sensorThe Foveon X3 sensor is a CMOS image sensor for digital cameras, designed by Foveon, Inc. and manufactured by National Semiconductor and Dongbu Electronics. It uses an array of photosites, each of which consists of three vertically stacked photodiodes, that are organized in a two-dimensional grid...
. Each location the
image sensorAn image sensor is a device that converts an optical image to an electric signal. It is used mostly in digital cameras and other imaging devices. An image sensor is typically a charge-coupled device or a complementary metal–oxide–semiconductor active-pixel sensor.- CCD vs CMOS :Today, most...
array has three stacked
active pixel sensorAn active-pixel sensor , also commonly written active pixel sensor, is an image sensor consisting of an integrated circuit containing an array of pixel sensors, each pixel containing a photodetector and an active amplifier. There are many types of active pixel sensors including the CMOS APS used...
s, utilizing the sensor's
siliconSilicon is the most common metalloid. It is a chemical element, which has the symbol Si and atomic number 14. A tetravalent metalloid, silicon is less reactive than its chemical analog carbon...
itself as the color filter, based on the wavelength-dependent absorption of light in silicon.
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