A charged coupled device (CCD) allows the transportation of electrically charged analog signals through different capacitors set up in a series. This device is controlled by a clock signal that oscillates between high and low states. The entire system acts as a shift register that has its inputs and outputs linked together in series, which allows a charged coupled device to be used as a way of delaying analog signals. The most common use of these devices is for photoelectric light sensors that are linked to parallel analog signals. This technology is the basis of how digital cameras, video recorders and picture phones operate.
In 1961, Eugene F. Lally, a researcher at the Jet Propulsion Laboratory in Pasadena, California, wrote a paper called Mosaic Guidance for Interplanetary Travel. He explored the idea of using a series of optical detectors that implemented digital processing to create a photograph. In 1969, scientists Willard Boyle and George E. Smith, working at AT&T Bell Labs in Murray Hill, New Jersey, developed a charged coupled device for use as a memory technology. Using this technology, other companies soon developed ways to capture the photoelectric effect and make electronic images.
The way that a charged coupled device works in capturing images is by focusing an image that is projected from a lens onto a photoactive capacitor array. This results in each capacitor accumulating an electric charge that is proportional to the light intensity of the image. This captures a two-dimensional image that is transferred to a charge amplifier, which in turn coverts it into voltage. This image is then stored digitally in a memory module and can be accessed later.
A basic charged coupled device is efficient in capturing luminance, but it has difficulty rendering color. To solve this problem, modern digital cameras use a device called a Bayer mask over the CCD. It links four pixels into blocks and filters different luminance levels as different colors. These pixels are colored, with one being red, one blue and two green, because the human eye can identify green more readily than other colors.
Another technology that was developed in the early 21st century involves high-resolution charged coupled device chips that can use more of the luminance color at different aperture sizes. It accomplishes this by implementing a device called a dichroic prism, which splits each color into its native components. Dichroic prisms have been used in some digital cameras and video cameras.
