Charge-coupled device, abbreviated CCD, is used to take digital photographs and videos. Digital videos and images are stored in numeric computer code. Cameras with CCD’s have largely replaced film cameras for many reasons. For one thing, CCD’s have a higher sensitivity to light than film has. In addition, images taken by CCD can easily be stored, modified, and viewed on computers and distributed over the Internet. Astronomers use CCD’s to record images with telescopes. Nearly all CCD’s are manufactured from silicon in much the same way as are other kinds of computer chips.
A CCD works by converting photons (fundamental particles of light) into electrons (fundamental particles of electric charge). Everything we see can be thought of as a pattern of photons. A CCD consists of a grid of millions of microscopic squares known as pixels. When a photon strikes an individual pixel, the pixel creates an electron. Pixels struck by more photons—that is, by brighter light—create more electrons and thus more electric charge. The CCD gathers the charges from all the pixels. This information forms a digital code representing the patterns of light striking the grid and thus the final image. The code can be recorded on a memory storage device. Computer programs can use the digital code to re-create the image on a screen.
Ordinary pixels respond only to the brightness of light, not to its color. To create color images, CCD’s use patterns of color filters. A common filter pattern uses red, blue, and green filters arranged on neighboring pixels. Each pixel can only detect one color of light. The pixels’ charges are later combined to give the appearance of a full-color image.
A CCD in a modern camera may have 2,000 rows and 2,000 columns of pixels, for a total of 4 million pixels. Such a camera is said to have 4 megapixels (millions of pixels). CCD’s with more pixels offer more detailed images. But other camera functions affect the quality of the image as well. Telescope cameras may use extremely large CCD’s or multiple CCD’s that contain more than a billion pixels altogether.
See also Boyle, Willard Sterling; Camcorder; Photography (Capturing digital images. ); Telescope (What telescopes do); Television (Creating television signals) (Solid-state cameras).
