CCD
A CCD or Charge-Coupled Device is an analog electronic device that can be used as the image sensor in place of film in an electronic camera or scanner. Many digital cameras use CCDs as their image sensor, although some use CMOS or other devices instead. The CCD was invented in 1969 at Bell Labs by Willard Boyle and George Smith[1]. Whilst the CCD is sensitive to light - and so can be used as an image sensor, it has also been used as a memory device. Some early cameras (e.g. Minolta RD-175) used more than one CCD - with a colour-separation prism or filter directing different colours of light to the individual sensors.
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| 3.2 megapixel CCD device of a Canon A75 digital compact camera |
CCD properties
The resolution of the image sensor governs the resolution of the camera, although some cameras can produce increased pixel counts using interpolation software - particularly with multi-CCD sensors.
The sensitivity to light of the sensor controls the ISO range that the camera can emulate. More sensitive sensors can also permit greater pixel bit widths, and so give better colour rendition.
The physical size of the sensor is important in several respects, for example:
- Larger sensors perform better at lower light levels - larger pixels can gather more photons at any given light level - so allowing lower-light photography and generally reducing noise.
- Just like larger film formats, larger sensors require longer focal-length - and hence larger - lenses, thus dictating the size of the camera. Larger lenses may also increase the cost of the camera.
- Larger sensors are likely to use more power - increasing battery requirements.
CCD makers
Many of the big camera makers or consumer electronics companies have their own CCD production facility, for example Sony and Fujifilm. Other companies specialise in making camera sensors, among them
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