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This information tells us how bright the light is at each pixel but that would only give us a black and white image. To get a color image, some digital cameras use a device called a beam splitter, which splits up the light into red, blue, and green beams and sends each one to a different CCD. This kind of camera can generate very high quality pictures because it closely measures the color of the image at each pixel. But because they constain 3 CCD's, these cameras are bulky and expensive. Most cheaper digital cameras use what's called a Bayer mask to generate a color image using only one CCD. For each group of four pixels in a CCD with a Bayer mask, one is filtered to measure red light, one blue, and two green. After the data is read from the CCD, a computer chip finds the actual color and intensity of each pixel by averaging the amount of red, green, and blue in the nearby pixels. This process is called interpolation.
The number of "megapixels" a camera has refers to how many millions of capacitors there are in the CCD to measure the intensity of light. A 4 megapixel camera would have approximately 4 million capacitors on the CCD. A typical CCD in a digital camera is about 4 by 5 millimeters. That means that each capacitor on a 4 megapixel CCD is only about than 2/1000 of a millimeter or 2 microns long.
CCDs are also used by astronomers to carefully measure the intensity and frequency of light coming from objects in outer space. In fact, most of the images from the Hubble Space Telescope are taken with CCDs.
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