CCD sensor

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CCD sensor

(Charge-Coupled Device sensor) An electronic memory that records the intensity of light as a variable charge. Although mostly replaced by CMOS sensors to capture images in cameras, camcorders and scanners, CCDs are still used in astronomy, microscopy and biomedical imaging because of their excellent sensitivity during long exposures.

CCDs are analog devices. Their charges equate to shades of light for monochrome images or shades of red, green and blue when used with color filters. Devices may use three CCDs, one for each of the red, green and blue colors.

Why Coupled?
The CCD comprises an array of imaging pixels and a matching array of storage pixels that are coupled together. After the imaging array is exposed to light, its charges are quickly transferred to the storage array. While the imaging CCDs are being exposed to the next picture, the storage CCDs from the last picture are being read out a row at a time to the analog-to-digital converters (A/D converters) that transform the voltages into binary data to be processed. Contrast with CMOS sensor. See Bayer pattern, X3, Super CCD, blooming and digital camera.

Charge-Coupling Methods
The storage CCDs are either a separate array (frame transfer) or individual photosites (interline transfer) coupled to each imaging photosite. The charges can be transferred faster with the interline method because each storage component is closer to its imaging counterpart.

CCDs Record Light
In a camera, CCDs take the place of film. They are exposed to light, recording the intensities, or shades, of light as variable charges. In the digital camera above, the variable, analog charges in the CCD are converted to binary data by analog-to-digital converter chips.

CCDs Are Sensitive
This CCD from Jet Propulsion Labs is used in astronomy. Sensing the output of telescopes, it detects ultraviolet light from distant planets. (Image courtesy of JPL's Microdevices Laboratory; Robert M. Brown, photographer)
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