In order to be able to process images by computers, images must first be made available in digital format. In a conventional camera, objects in a scene are focused by the optical elements on to a film, which is placed at the focal plane of the lens. The object is imaged onto the film when it is exposed to light from the object. In a digital camera, an array of photosensitive electronic sensors takes the place of the film. When the sensors are exposed to light, each sensor element develops an electrical charge that is proportional to the number of photons falling on the sensor. This electrical charge is then converted to a decimal number represented in a binary format. Figure 4-1 illustrates the principle ...