Skip to main content
Select Source:

charge-coupled device

charge-coupled device (CCD) Type of silicon chip designed to capture images. The CCD is divided into a number of microscopic areas (pixels), arranged in rows. When a photon hits a pixel, it knocks off an electron from a silicon atom, which becomes charged. An opposite charge in a layer on the base of the CCD confines this charged silicon atom, and in this way a charge builds up in each pixel relative to the number of photons hitting it 50 times a second. The contents of each pixel are read off, a row at a time, forming an electrical signal that can be used to create television pictures. CCDs are found in video cameras, fax machines, and digital cameras.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"charge-coupled device." World Encyclopedia. . Encyclopedia.com. 17 Oct. 2018 <http://www.encyclopedia.com>.

"charge-coupled device." World Encyclopedia. . Encyclopedia.com. (October 17, 2018). http://www.encyclopedia.com/environment/encyclopedias-almanacs-transcripts-and-maps/charge-coupled-device

"charge-coupled device." World Encyclopedia. . Retrieved October 17, 2018 from Encyclopedia.com: http://www.encyclopedia.com/environment/encyclopedias-almanacs-transcripts-and-maps/charge-coupled-device

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.

charge-coupled device

charge-coupled device (CCD) A light-sensitive semiconductor used to enhance images obtained from faint objects. It accumulates and temporarily stores charge at particular pixel locations when struck by photons. The pixels can then be moved, allowing them to be pieced together to form an image.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"charge-coupled device." A Dictionary of Earth Sciences. . Encyclopedia.com. 17 Oct. 2018 <http://www.encyclopedia.com>.

"charge-coupled device." A Dictionary of Earth Sciences. . Encyclopedia.com. (October 17, 2018). http://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/charge-coupled-device

"charge-coupled device." A Dictionary of Earth Sciences. . Retrieved October 17, 2018 from Encyclopedia.com: http://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/charge-coupled-device

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.

charge-coupled device

charge-coupled device See CCD.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"charge-coupled device." A Dictionary of Computing. . Encyclopedia.com. 17 Oct. 2018 <http://www.encyclopedia.com>.

"charge-coupled device." A Dictionary of Computing. . Encyclopedia.com. (October 17, 2018). http://www.encyclopedia.com/computing/dictionaries-thesauruses-pictures-and-press-releases/charge-coupled-device

"charge-coupled device." A Dictionary of Computing. . Retrieved October 17, 2018 from Encyclopedia.com: http://www.encyclopedia.com/computing/dictionaries-thesauruses-pictures-and-press-releases/charge-coupled-device

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.

Charge-Coupled Device

Charge-Coupled Device

How the devices work

Applications in astronomy

CCDs, professionals, and amateurs

Resources

Charge-coupled devices (CCDs) have made possible a revolution in image acquisition, first in scientific applications such as astronomy and more recently in consumer electronics, where they are the basis of the digital camera. A CCD consists of a checkerboard array of light-sensitive electronic elements. When CCDs are exposed to light, an image of the object being observed is formed; this image can be extracted from the CCD and stored on a computer for later analysis. CCDs are used in a variety of modern instruments, ranging from scanners and photocopiers to video cameras and digital still cameras. They have also transformed the way scientists measure and chart the universe.

How the devices work

All CCDs work on the same principle. The CCD surface is a grid of pixels (a contraction of picture elements). Small CCDs may have a grid of 256 x 256 pixels, while large CCDs may have pixel grids thousands of times larger. Although many CCD pixel grids are square, this is not always the case; scanners and photocopiers, for example, have a single line of pixels that passes over the picture or page of text being imaged. The pixels are tiny; some CCDs have pixels only 9 microns across, while others may have 27-micron pixels. The scale and resolution of the image a camera is able to form on the CCD depends both on the pixel size and the grid size. Regardless of the pixel or grid size, however, each pixel on the CCD has the ability to convert the light striking it into an electric signal. The voltage accumulated by each pixel during an exposure is directly proportional to the amount of light striking it. When the CCD is exposed to light for a length of time, an image of whatever is being observedwhether a distant galaxy or cars in a parking lotforms on the CCD as an array of differing electric voltages.

After an image has been recorded on the CCD, the device can be read out, meaning that the voltages are extracted from the CCD for storage on a computer. The analogy that is almost universally used to describe this process is the bucket brigade analogy. Picture each pixel on the CCD as a bucket with a certain amount of water in it. When the CCD is read out, the water in each row of buckets is emptied into the adjacent row. The water in the first row goes into a special row of storage buckets; the water in each bucket in the second row goes into its neighbor bucket in the first row, and so on across the whole CCD. Then, the amount of water in each of these buckets is emptied, measured, and stored in a computers memory. This process is repeated until all of the rows have been shifted into the storage buckets, emptied, and measured. If you now replace the water with electric voltages and replace the measurement of water with the digital measurement of the analog electric signal, you have the basic process by which an image is extracted from the CCD. The actual process of reading out the CCD is performed by fairly complicated and exquisitely synchronized electronics that move all the electric charges between the buckets, convert the analog voltages into digital numbers, and make the data available for storage on a computer.

Once the pixel outputs have been measured and stored on a computer, they can be used in a variety of ways. For simple line drawings, the image processing software may render the data from the CCD in black and white. For pictures, a 256-level grayscale may be appropriate. In either case, a grid of numbers, corresponding to the original light intensity, is present and can be analyzed in any way the person studying the image desires.

From the description above, it may seem that CCDs cannot be used for color imaging, since they respond only to light intensity. In fact, color CCDs are available, although they are used in video equipment such as camcorders and almost never in astronomy. If an astronomer wanted to create a color image using a CCD, the old practice of taking three images through three different color filters is still the usual way to go. True color CCDs have pixels with built-in filters alternating red, green, and blue. They can produce realtime color images, but they are undesirable for scientific work, because they introduce significant difficulties into the data analysis process, as well as reducing the effective resolution of the CCD by a factor of three.

Applications in astronomy

Astronomers began using charge-coupled devices in their work in the early 1980s, when the increasing power and clock speed of semiconductors, and the computers needed to drive the hardware and analyze the data, became both fast and affordable. Almost every field of astronomy was directly impacted by CCDs: for observations of asteroids, galaxies, stars, and planets, whether by direct imaging or the recording of spectra, the CCD rapidly became the detector of choice.

CCDs are also useful to astronomers because on average, CCDs are about ten times more light-sensitive than film. Astronomers are notorious for finding desperately faint objects to observe, so the CCD gave them the ability not only to see fainter objects than they could before but to reduce the amount of time spent tracking and observing a given object. A CCD camera can record in a 15-minute exposure the same information that would take a standard camera loaded with film two hours or more. While film typically records only 2-3% of the light that strikes it, charge-coupled device cameras can record between 50-80% of the light they detect. Furthermore, CCDs can capture light outside the visible spectrum, which film cannot do. The devices operate without darkrooms or chemicals, and the results can be reconstructed as soon as the information is loaded into an image processing program.

However, CCD cameras do have some drawbacks. The small size of the most affordable arrays results in a much smaller field of view. Large celestial bodies, such as the Moon, which are easily photographed with a 35 mm camera, become very difficult to reproduce as a single image with a CCD camera. Although larger arrays are coming to the market, they remain pricy and beyond the resources of the amateur astronomer. They require complicated systems to operate, and many of them have to be cooled to typical temperatures of 112°F (80°C) to reduce their background electronic noise to an acceptable level. Finally, color images for astronomical CCD cameras (unlike commercially-available video and digital still cameras) require three separate exposures for each filter used. The final image has to be created by combining the data from each exposure within the computer.

CCDs, professionals, and amateurs

With web-based star catalogues and other Internet and electronic resources such as the Hubble Guide Star Catalog and the Lowell Observatory Asteroid Database, professional and amateur astronomers have begun sharing resources and comparing data in hopes of creating a more accurate and complete picture of the heavens. Organizations such as the Amateur Sky Survey help individuals coordinate and share data with others. Thanks to CCDs, amateurs have often contributed as significantly to these projects as professional astronomers have. Paul Comba, an amateur based in Arizona, discovered and registered some 300 previously unknown asteroids in 199697, after adding a digital camera to his telescope. In 1998, astrophysics student Gianluca Masi recorded the existence of an unknown variable star, discovered with the use of his Kodak KAF-0400 CCD, mounted in a Santa Barbara Instrument Group ST-7 camera. CCDs help level the playing field in the science of astrometry, somewhat reducing the equipment barrier between the amateur and the professional.

Resources

BOOKS

Amico, Paola, et al. Scientific Detectors for Astronomy: The Beginning of a New Era. New York: Springer, 2006.

Howell, Steve B. Handbook of CCD Astronomy. Cambridge, UK: Cambridge University Press, 2006.

Kenneth R. Shepherd

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"Charge-Coupled Device." The Gale Encyclopedia of Science. . Encyclopedia.com. 17 Oct. 2018 <http://www.encyclopedia.com>.

"Charge-Coupled Device." The Gale Encyclopedia of Science. . Encyclopedia.com. (October 17, 2018). http://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/charge-coupled-device

"Charge-Coupled Device." The Gale Encyclopedia of Science. . Retrieved October 17, 2018 from Encyclopedia.com: http://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/charge-coupled-device

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.

Charge-Coupled Device

Charge-coupled device

Charge-coupled devices (CCDs) have made possible a revolution in image processing. They consist of a series of light-sensitive elements, called pixels, arranged in a square or rectangular array. When CCDs are exposed to light , an image of the object being observed is formed; this image can be extracted from the CCD and stored on a computer for later analysis. CCDs are used in a variety of modern instruments, ranging from scanners and photocopiers to video cameras and digital still cameras. They have transformed the way scientists measure and chart the universe. Because CCDs are available in a wide price range, they are accessible to amateurs as well as professionals, and enable both to make significant contributions to modern astronomy .


How the devices work

All CCDs work on the same principle. The CCD surface is a grid of pixels (pixel is a contraction for "picture element"). Small CCDs may have a grid of 256 x 256 pixels, while large CCDs may have 4,096 x 4,096 pixel grids. Although many CCD pixel grids are square, this is not always the case; scanners and photocopiers, for example, have a single line of pixels that passes over the picture or page of text being imaged. The pixels are tiny; some CCDs have pixels only 9 microns across, while others may have 27-micron pixels. The scale and resolution of the image a camera is able to form on the CCD depends both on the pixel size and the grid size. Regardless of the pixel or grid size, however, each pixel on the CCD has the ability to convert the light striking it into an electric signal. The voltage accumulated by each pixel during an exposure is directly proportional to the amount of light striking it. When the CCD is exposed to light for a length of time, an image of whatever is being observed—whether a distant galaxy or cars in a parking lot—forms on the CCD as an array of differing electric voltages.

After an image has been recorded on the CCD, the device can be "read out," meaning that the voltages are extracted from the CCD for storage on a computer. The analogy that is almost universally used to describe this process is the "bucket brigade" analogy. Picture each pixel on the CCD as a bucket with a certain amount of water in it. When the CCD is read out, the water in each row of buckets is emptied into the adjacent row. The water in the first row goes into a special row of storage buckets, the water in each bucket in the second row goes into its neighbor bucket in the first row, and so on across the whole CCD. Then, the amount of water in each of these buckets is emptied, measured, and stored in a computer's memory. This process is repeated until all of the rows have been shifted into the storage buckets, emptied, and measured. If you now replace the water with electric voltages, and replace the measurement of water with the digital measurement of the analog electric signal, you have the basic process by which an image is extracted from the CCD. The actual process of reading out the CCD is performed by fairly complicated and exquisitely synchronized electronics that move all the electric charges between the "buckets," convert the analog voltages into digital numbers, and make the data available for storage on a computer.

Once the pixel outputs have been measured and stored on a computer, they can be used in a variety of ways. For simple line drawings, the image processing software may render the data from the CCD in black and white. For pictures, a 256-level grayscale may be appropriate. In either case, a grid of numbers, corresponding to the original light intensity, is present and can be analyzed in any way the person studying the image desires.

From the description above, it may seem that CCDs cannot be used for color imaging, since they respond only to light intensity. In fact, color CCDs are available, although they are used in video equipment such as camcorders and almost never in astronomy. If an astronomer wanted to create a color image using a CCD, the old practice of taking three images through three different color filters is still the usual way to go. True color CCDs have pixels with built-in filters, alternating red, green, and blue. They can produce real-time color images, but they are undesirable for scientific work because they introduce significant difficulties into the data analysis process, as well as reducing the effective resolution of the CCD by a factor of three.


Applications in astronomy

Astronomers began using charge-coupled devices in their work in the early 1980s, when the increasing power and clock speed of semiconductors, and the computers needed to drive the hardware and analyze the data became both fast and affordable. Almost every field of astronomy was directly impacted by CCDs: for observations of asteroids, galaxies, stars, and planets, whether by direct imaging or the recording of spectra, the CCD rapidly became the detector of choice.

CCDs are also useful to astronomers because an average, CCDs are about ten times more light-sensitive than film. Astronomers are notorious for finding desperately faint objects to observe, so the CCD gave them the ability not only to see fainter objects than they could before, but to reduce the amount of time spent tracking and observing a given object. A CCD camera can record in a 15 minute exposure the same information that would take a standard camera loaded with film two hours or more. While film typically records only 2–3% of the light that strikes it, charge-coupled device cameras can record between 50–80% of the light they detect. Furthermore, CCDs can capture light outside the visible spectrum , which film cannot do. The devices operate without darkrooms or chemicals, and the results can be reconstructed as soon as the information is loaded into an image processing program.

However, CCD cameras do have some drawbacks. The small size of the most affordable arrays results in a much smaller field of view. Large celestial bodies such as the moon , which are easily photographed with a 35mm camera, become very difficult to reproduce as a single image with a CCD camera. Although larger arrays are coming to the market, they remain pricy and beyond the resources of the amateur astronomer. They require complicated systems to operate, any many of them have to be cooled to typical temperatures of -112°F (-80°C) to reduce their background electronic noise to an acceptable level. Finally, color images for astronomical CCD cameras (unlike commercially-available video and digital still cameras) require three separate exposures for each filter used. The final image has to be created by combining the data from each exposure within the computer.


CCDs, professionals, and amateurs

With web-based star catalogues and other Internet and electronic resources, such as the Hubble Guide Star Catalog and the Lowell Observatory Asteroid Database, professional and amateur astronomers have begun sharing resources and comparing data in hopes of creating a more accurate and complete picture of the heavens. Organizations such as the Amateur Sky Survey help individuals coordinate and share data with others. Thanks to CCDs, amateurs have often contributed as significantly to these projects as professional astronomers have. Paul Comba, an amateur based in Arizona, discovered and registered some 300 previously unknown asteroids in 1996–97, after adding a digital camera to his telescope . In 1998, astrophysics student Gianluca Masi recorded the existence of an unknown variable star, discovered with the use of his Kodak KAF-0400 CCD, mounted in a Santa Barbara Instrument Group ST-7 camera. CCDs help level the playing field in the science of astrometry , drastically reducing the equipment barrier between the amateur and the professional.


Resources

periodicals

di cicco, dennis. "measuring the sky with ccds." sky & telescope 94 (december 1997): 115-18.

gombert, glenn, and tom droege. "boldness: the amateur sky survey." sky & telescope 95 (february 1998): 42-45.

hannon, james. "warming up to digital imaging." sky & telescope 97 (march 1999): 129.

masi, gianluca. "ccds, small scopes, and the urban amateur." sky & telescope 95 (february 1998): 109-12.

terrance, gregory. "capture the sky on a ccd: digital imaging with a ccd camera is revolutionizing the way amateur astronomers record planets and galaxies." astronomy 28 (february 2000): 72.


Kenneth R. Shepherd

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"Charge-Coupled Device." The Gale Encyclopedia of Science. . Encyclopedia.com. 17 Oct. 2018 <http://www.encyclopedia.com>.

"Charge-Coupled Device." The Gale Encyclopedia of Science. . Encyclopedia.com. (October 17, 2018). http://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/charge-coupled-device-0

"Charge-Coupled Device." The Gale Encyclopedia of Science. . Retrieved October 17, 2018 from Encyclopedia.com: http://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/charge-coupled-device-0

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.