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[[File:Image sensor and motherbord nikon coolpix l2.JPG|thumb|Image sensor (upper left) on the motherboard of a {{nowrap|Nikon Coolpix L2 6 MP}}]]
The two main types of [[digital image]] sensors are the [[charge-coupled device]] (CCD) and the [[active-pixel sensor]] (CMOS sensor), [[semiconductor device fabrication|fabricated]] in [[complementary MOS]] (CMOS) or [[N-type semiconductor|N-type]] MOS ([[NMOS logic|NMOS]] or [[Live MOS]]) technologies. Both CCD and CMOS sensors are based on the [[MOS technology]],<ref>{{cite book |last1=Cressler |first1=John D. |title=Silicon Earth: Introduction to Microelectronics and Nanotechnology, Second Edition |date=2017 |publisher=[[CRC Press]] |isbn=978-1-351-83020-1 |chapter=Let There Be Light: The Bright World of Photonics |page=29 |chapter-url=https://books.google.com/books?id=i-5HDwAAQBAJ&pg=SA12-PA29}}</ref> with [[MOS capacitor]]s being the building blocks of a CCD,<ref>{{cite book |last1=Sze |first1=Simon Min |author1-link=Simon Sze |last2=Lee |first2=Ming-Kwei |chapter=MOS Capacitor and MOSFET |title=Semiconductor Devices: Physics and Technology : International Student Version |date=May 2012 |publisher=[[John Wiley & Sons]] |isbn=9780470537947 |chapter-url=https://www.oreilly.com/library/view/semiconductor-devices-physics/9780470537947/13_chap05.html |access-date=6 October 2019}}</ref> and [[MOSFET]] amplifiers being the building blocks of a CMOS sensor.<ref name="fossum93">{{cite book |last1=Fossum |first1=Eric R. |chapter=Active pixel sensors: Are CCDS dinosaurs? |author1-link=Eric Fossum |title=Charge-Coupled Devices and Solid State Optical Sensors III
Cameras integrated in small consumer products generally use CMOS sensors, which are usually cheaper and have lower power consumption in battery powered devices than CCDs.<ref>{{cite web |url=http://www.techhive.com/article/246931/cmos_is_winning_the_camera_sensor_battle_and_heres_why.html |title=CMOS Is Winning the Camera Sensor Battle, and Here's Why |website=techhive.com |date=2011-12-29 |access-date=2017-04-27 |url-status=live |archive-url=https://web.archive.org/web/20170501024004/http://www.techhive.com/article/246931/cmos_is_winning_the_camera_sensor_battle_and_heres_why.html |archive-date=2017-05-01 }}</ref> CCD sensors are used for high end broadcast quality video cameras, and CMOS sensors dominate in still photography and consumer goods where overall cost is a major concern. Both types of sensor accomplish the same task of capturing light and converting it into electrical signals.
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Each cell of a [[Charge-coupled device|CCD]] image sensor is an analog device. When light strikes the chip it is held as a small electrical charge in each [[photo sensor]]. The charges in the line of pixels nearest to the (one or more) output amplifiers are amplified and output, then each line of pixels shifts its charges one line closer to the amplifiers, filling the empty line closest to the amplifiers. This process is then repeated until all the lines of pixels have had their charge amplified and output.<ref name="auto">{{cite web|url=http://cpn.canon-europe.com/content/education/infobank/capturing_the_image/ccd_and_cmos_sensors.do|title=CCD and CMOS sensors|website=Canon Professional Network|access-date=28 April 2018|url-status=live|archive-url=https://web.archive.org/web/20180428122601/http://cpn.canon-europe.com/content/education/infobank/capturing_the_image/ccd_and_cmos_sensors.do|archive-date=28 April 2018}}</ref>
A CMOS image sensor has an amplifier for each pixel compared to the few amplifiers of a CCD. This results in less area for the capture of photons than a CCD, but this problem has been overcome by using microlenses in front of each photodiode, which focus light into the photodiode that would have otherwise hit the amplifier and not been detected.<ref name="auto"/>
Another design, a hybrid CCD/CMOS architecture (sold under the name "[[sCMOS]]") consists of CMOS readout integrated circuits (ROICs) that are bump bonded to a CCD imaging substrate – a technology that was developed for infrared [[staring array]]s and has been adapted to silicon-based detector technology.<ref name="test3">[http://www.scmos.com/ scmos.com] {{webarchive|url=https://web.archive.org/web/20120603082322/http://www.scmos.com/ |date=2012-06-03 }}, home page</ref> Another approach is to utilize the very fine dimensions available in modern CMOS technology to implement a CCD like structure entirely in CMOS technology: such structures can be achieved by separating individual poly-silicon gates by a very small gap; though still a product of research hybrid sensors can potentially harness the benefits of both CCD and CMOS imagers.<ref name="test4">[http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=4489895 ieee.org - CCD in CMOS] {{webarchive|url=https://web.archive.org/web/20150622073305/http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=4489895 |date=2015-06-22 }} Padmakumar R. Rao et al., "CCD structures implemented in standard 0.18 μm CMOS technology"</ref>
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{{see also|EMVA1288}}
<!--[[File:Removed EOS 350D IR-blocking filter.jpg|thumb|An infrared-blocking filter removed from a [[Canon EOS 350D]] [[Digital single-lens reflex camera|DSLR]]]]
There are many parameters that can be used to evaluate the performance of an image sensor, including [[dynamic range]], [[signal-to-noise ratio]], and low-light sensitivity. For sensors of comparable types, the signal-to-noise ratio and dynamic range improve as the [[Image sensor format#Sensor size|size]] increases. It is because in a given integration (exposure) time, more photons hit the pixel with larger area.
==Exposure-time control==
[[Exposure time]] of image sensors is generally controlled by either a conventional mechanical [[shutter (photography)|shutter]], as in film cameras, or by an [[electronic shutter]].
▲[[Exposure time]] of image sensors is generally controlled by either a conventional mechanical [[shutter (photography)|shutter]], as in film cameras, or by an [[electronic shutter]]. Electronic shuttering can be "global," in which case the entire image sensor area's accumulation of photoelectrons starts and stops simultaneously, or "rolling" in which case the exposure interval of each row immediate precedes that row's readout, in a process that "rolls" across the image frame (typically from top to bottom in landscape format). Global electronic shuttering is less common, as it requires "storage" circuits to hold charge from the end of the exposure interval until the readout process gets there, typically a few milliseconds later.<ref>{{cite book |last1=Nakamura |first1=Junichi |title=Image Sensors and Signal Processing for Digital Still Cameras |date=2005 |publisher=CRC Press |isbn=9781420026856 |pages=169–172 |url=https://books.google.com/books?id=UY6QzgzgieYC&pg=PA170}}</ref>
==Color separation==
[[
[[File:Absorption-X3.svg
There are several main types of color image sensors, differing by the type of color-separation mechanism:
* '''Integral color sensors'''<ref>{{Cite conference <!-- Citation bot no -->|last=Dillon |first=Peter |title=1976 International Electron Devices Meeting |chapter=Integral color filter arrays for solid state imagers |date=Dec 1976 |chapter-url=https://ieeexplore.ieee.org/document/1478779 |conference=Technical Digest International Electron Device Meeting (IEDM), Washington, DC, Dec 1976 |pages=400–403 |doi=10.1109/IEDM.1976.189067 |s2cid=35103154 |via=IEEE}}</ref> use a [[color filter array]] fabricated on top of a single monochrome CCD or CMOS image sensor.
* '''[[Foveon X3 sensor]]''', using an array of layered pixel sensors, separating light via the inherent wavelength-dependent absorption property of silicon, such that every ___location senses all three color channels. This method is similar to how color film for photography works.
* '''[[Three-CCD camera|3CCD]]''', using three discrete image sensors, with the color separation done by a [[dichroic prism]].
==Specialty sensors==
[[File:A deep infrared view of the Orion Nebula from HAWK-I - Eso1625a.jpg|right|thumb|Infrared view of the [[Orion Nebula]] taken by [[ESO]]'s HAWK-I, a cryogenic wide-field imager<ref>{{cite web|title=Deepest Ever Look into Orion|url=http://www.eso.org/public/news/eso1625/|access-date=13 July 2016|url-status=live|archive-url=https://web.archive.org/web/20160713170150/http://www.eso.org/public/news/eso1625/|archive-date=13 July 2016}}</ref>]]
Special sensors are used in various applications such as creation of [[multi-spectral image]]s, [[Laryngoscopy|video laryngoscopes]], [[gamma camera]]s, [[Flat-panel detector]]s and other [[sensor array]]s for [[x-ray]]s, [[microbolometer]] arrays in [[thermography]],
While in general, digital cameras use a flat sensor, Sony prototyped a curved sensor in 2014 to reduce/eliminate [[Petzval field curvature]] that occurs with a flat sensor. Use of a curved sensor allows a shorter and smaller diameter of the lens with reduced elements and components with greater aperture and reduced light fall-off at the edge of the photo.<ref>{{cite web |url=https://www.engadget.com/2014/07/08/sony-shows-off-first-picture-taken-with-curved-sensor/ |title=Sony's first 'curved sensor' photo may herald better images, cheaper lenses |first=Steve |last=Dent |date=8 July 2014 |access-date=July 8, 2014 |url-status=live |archive-url=https://web.archive.org/web/20140711224002/http://www.engadget.com/2014/07/08/sony-shows-off-first-picture-taken-with-curved-sensor/ |archive-date=July 11, 2014 }}</ref>
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