Charge-Coupled Device (CCD)

A charge-coupled device (CCD) is a device for the movement of electrical charge, usually from within the device to an area where the charge can be manipulated, for example conversion into a digital value. This is achieved by "shifting" the signals between stages within the device one at a time. CCDs move charge between capacitive bins in the device, with the shift allowing for the transfer of charge between bins.
Often the device is integrated with an image sensor, such as a photoelectric device to produce the charge that is being read, thus making the CCD a major technology for digital imaging. Although CCDs are not the only technology to allow for light detection, CCDs are widely used in professional, medical, and scientific applications where high-quality image data is required.

3 CCD Camera

A single CCD Image

A three-CCD camera is a camera whose imaging system uses three separate charge-coupled devices (CCDs), each one taking a separate measurement of red, green, or blue light. Light coming into the lens is split by a trichroic prism assembly, which directs the appropriate wavelength ranges of light to their respective CCDs. The system is employed by some still cameras, video cameras, telecine systems and camcorders.
Compared to cameras with only one CCD, three-CCD cameras generally provide superior image quality and resolution. By taking separate readings of red, green, and blue values for each pixel, three-CCD cameras achieve much better precision than single-CCD cameras. By contrast, almost all single-CCD cameras use a Bayer filter, which allows them to detect only one-third of the color information for each pixel. The other two-thirds must be interpolated with a demosaicing algorithm to 'fill in the gaps', resulting in a much lower effective resolution.
The combination of the three sensors can be done in the following ways:

• Composite sampling, where the three sensors are perfectly aligned to avoid any color artifact when recombining the information from the three color planes
• Pixel shifting, where the three sensors are shifted by a fraction of a pixel. After recombining the information from the three sensors, higher spatial resolution can be achieved. Pixel shifting can be horizontal only to provide higher horizontal resolution in standard resolution camera, or horizontal and vertical to provide high resolution image using standard resolution imager for example. The alignment of the three sensors can be achieved by micro mechanical movements of the sensors relative to each other.
• Arbitrary alignment, where the random alignment errors due to the optics are comparable to or larger than the pixel size.

Three-CCD cameras are generally more expensive than single-CCD cameras because they require three times as many elements to form the image detector, and because they require a precision color-separation beam-splitter optical assembly.
The concept of cameras using three image pickups, one for each primary color, was first developed for color photography on three glass plates in the late nineteenth century, and in the 1960s through 1980s was the dominant method to record color images in television, as other possibilities to record more than one color on the video camera tube were difficult.

Three-CCD cameras are often referred to as "three-chip" cameras; this term is actually more descriptive and inclusive, since it includes cameras that use CMOS active pixel sensors instead of CCDs. Camcorders with 3 chips were called "3CCD" earlier and some are still called "3MOS" (derived from 3xCMOS, Panasonic) today.