What are CCD's?

Ok. You've just bought a video camera, and you sit down with your coffee(or beverage of choice) to read the instructions on how to use the thing. It states that your 3CCD camera, is capable of capturing amazing quality images. Well what is a CCD? A CCD is a small, rectangular piece of silicon rather than a piece of film to receive incoming light. This is a special piece of silicon called a charge-coupled device or CCD. This silicon wafer is an electronic component which has been micro-manufactured and segmented into an array of individual light-sensitive cells called "photosites." Each photosite is one element of the whole picture that is formed, thus it is called a picture element, or "pixel." The more common CCDs found in camcorders and other retail devices have a pixel array that is a few hundred photosites high by a few hundred photosites wide (e.g., 500x300, or 320x200), utilizing tens of thousands of pixels. Since most CCDs are only about 1/4" or 1/3" square, each of the many thousands of pixels are only about 10 millionths of a meter or 4 ten-thousandths of an inch wide. That's pretty small!

The CCD photosites accomplish their task of sensing incoming light through the photoelectric effect, which is the action certain materials do to release an electron when hit with a photon of light. The electrons emitted within the CCD are fenced within nonconductive boundaries, so that they remain within the area of the photon strike. As long as light is allowed to collect on a photosite, electrons will accumulate in that pixel. When the source of light is extinguished (e.g., the shutter is closed), simple electronic circuitry and a microprocessor or computer are used to unload the CCD array, count the electrons in each pixel, and process the resulting data into an image on a video monitor or other media output.
Camcorders make color images by merging the data taken simultaneously by groups of adjacent pixels covered by red, green, and blue filters. In the case of a camcorder with 3CCD's, there will be a seperate CCD for each of the filters, red, green, and blue.

In the final stages of image production, the light frame (object image) is adjusted by first having an appropriate dark frame subtracted and then having an appropriate flat field divided into the image. This process is called image calibration and results in a truer, less noisy image. Simple. :)