Charge Coupled Device (CCD), either assembled as a linear or two-dimensional array of light sensitive elements. Light is converted to an electrical charge in a linear fashion – proportional to the brightness impinging on each cell. The cells are coupled to a scanning system which, after analog to digital conversion, presents the image as a series of binary digits.
Typically the charge created on each cell is shuffled along to the end of its line where it is measured by an ADC that outputs a digital number corresponding to the charge, and hence, the brightness. This handling of the charge exposes it to noise and early CCD arrays were unable to work over a wide range of brightness. Now they offer low noise, high resolution imaging for television and digital cinematography.
See also: CMOS