What Is a Color Filter Array?

Bayer filter (English: Bayer filter) is a mosaic color filter array formed by RGB color filters arranged on the grid of light sensor components. Most of the single-chip digital image sensors used in digital cameras, video recorders, scanners, etc., use this particular arrangement of color filter arrays to make color images. This color filter arrangement has 50% green, 25% red, and 25% blue, so it is also called RGBG , GRGB , or RGGB .

Bayer filter (English: Bayer filter)

In the 1976 patent (US Patent No. 3,971,065), Bryce Bayer referred to the green light sensor as the light-sensitive detection component, and red and blue as the color-sensitive detection component. He uses twice as many green components as red or blue to imitate

Demosaicing has different implementations. Some simple ways are to interpolate the pixel values of adjacent pixels of the same color. For example, when the chip exposes an image, each pixel can be read out. The pixel of the green filter accurately measures the green component, while the pixel's red and blue components are obtained from neighboring areas. The red value of a green pixel can be calculated by interpolation of two adjacent red pixels; similarly, the blue value can also be calculated by interpolating two adjacent blue pixels.

This simple method performs well when the color is constant or uniform, but it produces noise at sudden changes in color and brightness, such as Color bleeding, which is particularly noticeable at sharp corners. Therefore, other demosaicing methods try to identify high-contrast edges and then just interpolate along these edges without crossing the edges.

Other algorithms assume that the color of a region in the image is relatively constant, even if the lighting is different, then the color channels are highly correlated. Therefore, the green channel is interpolated first, then red, and then blue, so the color ratio of red-green to blue-green is constant. There are other ways to set the image content differently and try to calculate the value of the missing color.

The small details in the image that are close to the resolution of the digital sensor will cause problems with the demosaic algorithm, which is likely to produce results that are not like the original image. The most common noise is

Bayer filters are used in consumer digital cameras around the world. Other filters are CYGM filters (Cyan, Yellow, Green, Magenta) and RGBE filters (Red, Green, Blue, Emerald), A similar demosaic process is also required. The arrangement of the Foveon X3 image sensor (stacking the red, green, and blue image sensors vertically instead of using a normal mosaic image) and three separate CCDs (one CCD corresponds to one color) does not require demosaicing.

Bayer filter full color unit

On June 14, 2007, Eastman Kodak released a replacement for Bayer color filters that enhance digital cameras with a full-color unit that detects all visible wavelengths and collects a large amount of light entering the image sensor The image sensor senses light. They showed several patterns, but none of them were repetitive combinations as small as the Bayer image 2x2. ^[2]

Another US patent filed by Edward T. Chang in 2007 is a color filter composed of a 2x2 block pixel image sensor. Each block is constructed of a red, a blue, a green, and a transparent pixel. to make. This setup is intended to enhance the infrared sensing and thus the overall sensing power. Kodak applied for patents earlier.

Such units have been used in "CMYW" (Cyan, Magenta, Yellow, White) and "RGBW" (red, green, blue, white) image sensors, but Kodak has not compared the newly designed color filter image.

EXR Bayer filter "EXR" color filter array for Fuji cameras

Fujifilm's EXR color filter array can be used for CCD manufacturing (SuperCCD) and CMOS (BSI CMOS). Like SuperCCD, the color filter itself rotates 45 degrees. Unlike the common Bayer filter design, there are always two adjacent photosensitive units that detect the same color. This design is to promote pixel binning, that is, to merge two adjacent photosensitive units to make the image sensor itself more sensitive to light. Another reason is that the image sensor can record two different exposure values and then combine them to produce an image with a larger dynamic range. The bottom line has two read-out channels that can carry information from the image sensor every other column. In this way, the "EXR" color filter array can be used as two interlaced image sensors, and the exposure times can be different from each other. You can deliberately under-expose half of the photosensitive units to capture the brighter areas of the scene completely. The obtained glare information can be mixed with the output of the other half of the image sensor which records the full exposure, and the spatial proximity of similar color photosensitive units can be used again.

"X-Trans" Bayer Filter "X-Trans" Color Filter for Fuji Cameras

The Fuji X-Trans CMOS image sensor is used in many Fujifilm X-series cameras. It is said that it has better resistance to color moire than the Bayer filter, so the camera can be made without anti-aliasing filters ( Anti-aliasing filter). This allows cameras using this image sensor to have higher resolutions when the number of pixels is the same. This new design also claims that because each line has red, blue, and green pixels, false colors can be reduced, and the semi-random arrangement of pixels is said to produce a more film-like texture.