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An image sensor or imager is a sensor that detects and conveys information used to make an
image An image is a visual representation of something. It can be two-dimensional, three-dimensional, or somehow otherwise feed into the visual system to convey information. An image can be an artifact, such as a photograph or other two-dimensio ...
. It does so by converting the variable
attenuation In physics, attenuation (in some contexts, extinction) is the gradual loss of flux intensity through a medium. For instance, dark glasses attenuate sunlight, lead attenuates X-rays, and water and air attenuate both light and sound at var ...
of light
wave In physics, mathematics, and related fields, a wave is a propagating dynamic disturbance (change from equilibrium) of one or more quantities. Waves can be periodic, in which case those quantities oscillate repeatedly about an equilibrium (re ...
s (as they pass through or reflect off objects) into signals, small bursts of current that convey the information. The waves can be light or other
electromagnetic radiation In physics, electromagnetic radiation (EMR) consists of waves of the electromagnetic (EM) field, which propagate through space and carry momentum and electromagnetic radiant energy. It includes radio waves, microwaves, infrared, (visib ...
. Image sensors are used in electronic imaging devices of both analog and
digital Digital usually refers to something using discrete digits, often binary digits. Technology and computing Hardware *Digital electronics, electronic circuits which operate using digital signals ** Digital camera, which captures and stores digital ...
types, which include digital cameras,
camera module {{unreferenced, date=August 2017 A camera module is an image sensor integrated with a lens, control electronics, and an interface like CSI, Ethernet or plain raw low-voltage differential signaling. See also * IP camera * Mobile Industry Process ...
s, camera phones,
optical mouse An optical mouse is a computer mouse which uses a light source, typically a light-emitting diode (LED), and a light detector, such as an array of photodiodes, to detect movement relative to a surface. Variations of the optical mouse have largely r ...
devices, medical imaging equipment, night vision equipment such as
thermal imaging Infrared thermography (IRT), thermal video and/or thermal imaging, is a process where a thermal camera captures and creates an image of an object by using infrared radiation emitted from the object in a process, which are examples of infrared ...
devices,
radar Radar is a detection system that uses radio waves to determine the distance (''ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, Marine radar, ships, spacecraft, guided missiles, motor v ...
,
sonar Sonar (sound navigation and ranging or sonic navigation and ranging) is a technique that uses sound propagation (usually underwater, as in submarine navigation) to navigate, measure distances (ranging), communicate with or detect objects on o ...
, and others. As technology changes, electronic and digital imaging tends to replace chemical and analog imaging. The two main types of electronic image sensors are the charge-coupled device (CCD) and the active-pixel sensor (
CMOS Complementary metal–oxide–semiconductor (CMOS, pronounced "sea-moss", ) is a type of metal–oxide–semiconductor field-effect transistor (MOSFET) fabrication process that uses complementary and symmetrical pairs of p-type and n-type MOSF ...
sensor). Both CCD and CMOS sensors are based on metal–oxide–semiconductor (MOS) technology, with CCDs based on MOS capacitors and CMOS sensors based on
MOSFET The metal–oxide–semiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET) is a type of field-effect transistor (FET), most commonly fabricated by the controlled oxidation of silicon. It has an insulated gate, the voltage of which d ...
(MOS field-effect transistor)
amplifiers An amplifier, electronic amplifier or (informally) amp is an electronic device that can increase the magnitude of a signal (a time-varying voltage or current). It may increase the power significantly, or its main effect may be to boost th ...
. Analog sensors for invisible radiation tend to involve
vacuum tube A vacuum tube, electron tube, valve (British usage), or tube (North America), is a device that controls electric current flow in a high vacuum between electrodes to which an electric potential difference has been applied. The type known as ...
s of various kinds, while digital sensors include
flat-panel detector Flat-panel detectors are a class of solid-state x-ray digital radiography devices similar in principle to the image sensors used in digital photography and video. They are used in both projectional radiography and as an alternative to x-ray ima ...
s.


CCD vs. CMOS sensors

The two main types of digital image sensors are the charge-coupled device (CCD) and the active-pixel sensor (CMOS sensor), fabricated in complementary MOS (CMOS) or N-type MOS ( NMOS or
Live MOS The Live MOS sensor is a brand name of an NMOS Image sensorOlympus E-330 EVOLT Review
) technologies. Both CCD and CMOS sensors are based on MOS technology, with MOS capacitors being the building blocks of a CCD, and
MOSFET The metal–oxide–semiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET) is a type of field-effect transistor (FET), most commonly fabricated by the controlled oxidation of silicon. It has an insulated gate, the voltage of which d ...
amplifiers being the building blocks of a CMOS sensor. 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. 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. Each cell of a CCD image sensor is an analog device. When light strikes the chip it is held as a small electrical charge in each
photo sensor Photodetectors, also called photosensors, are sensors of light or other electromagnetic radiation. There is a wide variety of photodetectors which may be classified by mechanism of detection, such as photoelectric or photochemical effects, or by ...
. 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. 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. Some CMOS imaging sensors also use Back-side illumination to increase the number of photons that hit the photodiode. CMOS sensors can potentially be implemented with fewer components, use less power, and/or provide faster readout than CCD sensors. They are also less vulnerable to static electricity discharges. 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 A staring array, also known as staring-plane array or focal-plane array (FPA), is an image sensor consisting of an array (typically rectangular) of light-sensing pixels at the focal plane of a lens. FPAs are used most commonly for imaging purp ...
s and has been adapted to silicon-based detector technology.scmos.com
, home page
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.ieee.org - CCD in CMOS
Padmakumar R. Rao et al., "CCD structures implemented in standard 0.18 µm CMOS technology"


Performance

There are many parameters that can be used to evaluate the performance of an image sensor, including
dynamic range Dynamic range (abbreviated DR, DNR, or DYR) is the ratio between the largest and smallest values that a certain quantity can assume. It is often used in the context of signals, like sound and light. It is measured either as a ratio or as a base ...
, signal-to-noise ratio, and low-light sensitivity. For sensors of comparable types, the signal-to-noise ratio and dynamic range improve as the
size Size in general is the magnitude or dimensions of a thing. More specifically, ''geometrical size'' (or ''spatial size'') can refer to linear dimensions ( length, width, height, diameter, perimeter), area, or volume. Size can also be me ...
increases.


Exposure-time control

Exposure time of image sensors is generally controlled by either a conventional mechanical shutter, as in film cameras, or by an
electronic shutter In photography, a shutter is a device that allows light to pass for a determined period, exposing photographic film or a photosensitive digital sensor to light in order to capture a permanent image of a scene. A shutter can also be used to allow p ...
. 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.


Color separation

There are several main types of color image sensors, differing by the type of color-separation mechanism: * Bayer-filter sensor, low-cost and most common, using a color filter array that passes red, green, and blue light to selected pixel sensors. Each individual sensor element is made sensitive to red, green, or blue by means of a color gel made of chemical dyes patterned over the elements. The most common filter matrix, the Bayer pattern, uses two green pixels for each red and blue. This results in less resolution for red and blue colors. The missing color samples may interpolated using a demosaicing algorithm, or ignored altogether by
lossy compression In information technology, lossy compression or irreversible compression is the class of data compression methods that uses inexact approximations and partial data discarding to represent the content. These techniques are used to reduce data si ...
. In order to improve color information, techniques like
color co-site sampling Colour co-site sampling is a system of photographic colour sensing, wherein 4, 16 or 36 images are collected from the sensor and merged to form a single image. Each subsequent image physically moves the sensor by exactly one pixel, in order to col ...
use a piezo mechanism to shift the color sensor in pixel steps. * 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. *
3CCD A three-CCD (3CCD) camera is a camera whose imaging system uses three separate charge-coupled devices (CCDs), each one receiving filtered red, green, or blue color ranges. Light coming in from the lens is split by a beam-splitter prism into th ...
, using three discrete image sensors, with the color separation done by a
dichroic prism A dichroic prism is a prism that splits light into two beams of differing wavelength (colour). A trichroic prism assembly combines two dichroic prisms to split an image into 3 colours, typically as red, green and blue of the RGB colour model. ...
. The dichroic elements provide a sharper color separation, thus improving color quality. Because each sensor is equally sensitive within its passband, and at full resolution, 3-CCD sensors produce better color quality and better low light performance. 3-CCD sensors produce a full 4:4:4 signal, which is preferred in
television broadcasting A television network or television broadcaster is a telecommunications network for distribution of television program content, where a central operation provides programming to many television stations or pay television providers. Until the mid- ...
, video editing and chroma key visual effects.


Specialty sensors

Special sensors are used in various applications such as
thermography Infrared thermography (IRT), thermal video and/or thermal imaging, is a process where a thermal camera captures and creates an image of an object by using infrared radiation emitted from the object in a process, which are examples of infrared i ...
, creation of multi-spectral images, video laryngoscopes,
gamma camera A gamma camera (γ-camera), also called a scintillation camera or Anger camera, is a device used to image gamma radiation emitting radioisotopes, a technique known as scintigraphy. The applications of scintigraphy include early drug development ...
s, sensor arrays for
x-ray An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10  nanometers, corresponding to frequencies in the range 30&nb ...
s, and other highly sensitive arrays for
astronomy Astronomy () is a natural science that studies celestial objects and phenomena. It uses mathematics, physics, and chemistry in order to explain their origin and evolution. Objects of interest include planets, moons, stars, nebulae, g ...
. While in general digital cameras use a flat sensor, Sony prototyped a curved sensor in 2014 to reduce/eliminate
Petzval field curvature Petzval field curvature, named for Joseph Petzval, describes the optical aberration in which a flat object normal to the optical axis (or a non-flat object past the hyperfocal distance) cannot be brought properly into focus on a flat image plan ...
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.


History

Early analog sensors for visible light were video camera tubes. They date back to the 1930s, and several types were developed up until the 1980s. By the early 1990s, they had been replaced by modern
solid-state Solid state, or solid matter, is one of the four fundamental states of matter. Solid state may also refer to: Electronics * Solid-state electronics, circuits built of solid materials * Solid state ionics, study of ionic conductors and their ...
CCD image sensors. The basis for modern solid-state image sensors is MOS technology, which originates from the invention of the MOSFET by Mohamed M. Atalla and Dawon Kahng at
Bell Labs Nokia Bell Labs, originally named Bell Telephone Laboratories (1925–1984), then AT&T Bell Laboratories (1984–1996) and Bell Labs Innovations (1996–2007), is an American industrial research and scientific development company owned by mul ...
in 1959. Later research on MOS technology led to the development of solid-state
semiconductor A semiconductor is a material which has an electrical conductivity value falling between that of a conductor, such as copper, and an insulator, such as glass. Its resistivity falls as its temperature rises; metals behave in the opposite way ...
image sensors, including the charge-coupled device (CCD) and later the active-pixel sensor (
CMOS Complementary metal–oxide–semiconductor (CMOS, pronounced "sea-moss", ) is a type of metal–oxide–semiconductor field-effect transistor (MOSFET) fabrication process that uses complementary and symmetrical pairs of p-type and n-type MOSF ...
sensor). The passive-pixel sensor (PPS) was the precursor to the active-pixel sensor (APS). A PPS consists of passive pixels which are read out without amplification, with each pixel consisting of a photodiode and a
MOSFET The metal–oxide–semiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET) is a type of field-effect transistor (FET), most commonly fabricated by the controlled oxidation of silicon. It has an insulated gate, the voltage of which d ...
switch. It is a type of
photodiode array A photodiode is a light-sensitive semiconductor diode. It produces current when it absorbs photons. The package of a photodiode allows light (or infrared or ultraviolet radiation, or X-rays) to reach the sensitive part of the device. The packag ...
, with pixels containing a p-n junction, integrated
capacitor A capacitor is a device that stores electrical energy in an electric field by virtue of accumulating electric charges on two close surfaces insulated from each other. It is a passive electronic component with two terminals. The effect of ...
, and MOSFETs as selection
transistors upright=1.4, gate (G), body (B), source (S) and drain (D) terminals. The gate is separated from the body by an insulating layer (pink). A transistor is a semiconductor device used to Electronic amplifier, amplify or electronic switch, switch ...
. A photodiode array was proposed by G. Weckler in 1968. This was the basis for the PPS. These early photodiode arrays were complex and impractical, requiring selection transistors to be fabricated within each pixel, along with on-chip multiplexer circuits. The
noise Noise is unwanted sound considered unpleasant, loud or disruptive to hearing. From a physics standpoint, there is no distinction between noise and desired sound, as both are vibrations through a medium, such as air or water. The difference aris ...
of photodiode arrays was also a limitation to performance, as the photodiode readout bus capacitance resulted in increased noise level. Correlated double sampling (CDS) could also not be used with a photodiode array without external
memory Memory is the faculty of the mind by which data or information is encoded, stored, and retrieved when needed. It is the retention of information over time for the purpose of influencing future action. If past events could not be remember ...
. However, in 1914 Deputy Consul General Carl R. Loop, reported to the state department in a Consular Report on Archibald M. Low's Televista system that "It is stated that the selenium in the transmitting screen may be replaced by any diamagnetic material". In June 2022, Samsung Electronics announced that it had created a 200 million pixel image sensor. The 200MP ISOCELL HP3 has 0.56 micrometer pixels with Samsung reporting that previous sensors had 064 micrometer pixels, a 12% decrease since 2019. The new sensor contains 200 million pixels in a 2 x 1.4 inch lens.


Charge-coupled device

The charge-coupled device (CCD) was invented by
Willard S. Boyle Willard Sterling Boyle, (August 19, 1924May 7, 2011) was a Canadian physicist. He was a pioneer in the field of laser technology and co-inventor of the charge-coupled device. As director of Space Science and Exploratory Studies at Bellcomm he h ...
and George E. Smith at Bell Labs in 1969. While researching MOS technology, they realized that an electric charge was the analogy of the magnetic bubble and that it could be stored on a tiny MOS capacitor. As it was fairly straightforward to fabricate a series of MOS capacitors in a row, they connected a suitable voltage to them so that the charge could be stepped along from one to the next. The CCD is a semiconductor circuit that was later used in the first digital video cameras for
television broadcasting A television network or television broadcaster is a telecommunications network for distribution of television program content, where a central operation provides programming to many television stations or pay television providers. Until the mid- ...
. Early CCD sensors suffered from
shutter lag In photography, shutter lag is the delay between triggering the shutter and when the photograph is actually recorded. This is a common problem in the photography of fast-moving objects or animals and people in motion. The term narrowly refers only ...
. This was largely resolved with the invention of the pinned photodiode (PPD). It was invented by Nobukazu Teranishi, Hiromitsu Shiraki and Yasuo Ishihara at
NEC is a Japanese multinational information technology and electronics corporation, headquartered in Minato, Tokyo. The company was known as the Nippon Electric Company, Limited, before rebranding in 1983 as NEC. It provides IT and network soluti ...
in 1980. It was a photodetector structure with low lag, low
noise Noise is unwanted sound considered unpleasant, loud or disruptive to hearing. From a physics standpoint, there is no distinction between noise and desired sound, as both are vibrations through a medium, such as air or water. The difference aris ...
, high
quantum efficiency The term quantum efficiency (QE) may apply to incident photon to converted electron (IPCE) ratio of a photosensitive device, or it may refer to the TMR effect of a Magnetic Tunnel Junction. This article deals with the term as a measurement of ...
and low dark current. In 1987, the PPD began to be incorporated into most CCD devices, becoming a fixture in consumer electronic video cameras and then
digital still camera A digital camera is a camera that captures photographs in digital memory. Most cameras produced today are digital, largely replacing those that capture images on photographic film. Digital cameras are now widely incorporated into mobile devic ...
s. Since then, the PPD has been used in nearly all CCD sensors and then CMOS sensors.


Active-pixel sensor

The NMOS active-pixel sensor (APS) was invented by
Olympus Olympus or Olympos ( grc, Ὄλυμπος, link=no) may refer to: Mountains In antiquity Greece * Mount Olympus in Thessaly, northern Greece, the home of the twelve gods of Olympus in Greek mythology * Mount Olympus (Lesvos), located in Le ...
in Japan during the mid-1980s. This was enabled by advances in MOS
semiconductor device fabrication Semiconductor device fabrication is the process used to manufacture semiconductor devices, typically integrated circuit (IC) chips such as modern computer processors, microcontrollers, and memory chips such as NAND flash and DRAM that are ...
, with MOSFET scaling reaching smaller micron and then sub-micron levels. The first NMOS APS was fabricated by Tsutomu Nakamura's team at Olympus in 1985. The
CMOS Complementary metal–oxide–semiconductor (CMOS, pronounced "sea-moss", ) is a type of metal–oxide–semiconductor field-effect transistor (MOSFET) fabrication process that uses complementary and symmetrical pairs of p-type and n-type MOSF ...
active-pixel sensor (CMOS sensor) was later improved by a group of scientists at the
NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeedin ...
Jet Propulsion Laboratory The Jet Propulsion Laboratory (JPL) is a Federally funded research and development centers, federally funded research and development center and NASA field center in the City of La Cañada Flintridge, California, La Cañada Flintridge, California ...
in 1993. By 2007, sales of CMOS sensors had surpassed CCD sensors. By the 2010s, CMOS sensors largely displaced CCD sensors in all new applications.


Other image sensors

The first commercial digital camera, the Cromemco Cyclops in 1975, used a 32×32 MOS image sensor. It was a modified MOS dynamic RAM ( DRAM) memory chip. MOS image sensors are widely used in
optical mouse An optical mouse is a computer mouse which uses a light source, typically a light-emitting diode (LED), and a light detector, such as an array of photodiodes, to detect movement relative to a surface. Variations of the optical mouse have largely r ...
technology. The first optical mouse, invented by
Richard F. Lyon Richard "Dick" Francis Lyon (born 1952) is an American inventor, scientist, and engineer. He is one of the two people who independently invented the first optical mouse devices in 1980. He has worked in many aspects of signal processing and wa ...
at
Xerox Xerox Holdings Corporation (; also known simply as Xerox) is an American corporation that sells print and digital document products and services in more than 160 countries. Xerox is headquartered in Norwalk, Connecticut (having moved from St ...
in 1980, used a 5µm NMOS
integrated circuit An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuits on one small flat piece (or "chip") of semiconductor material, usually silicon. Large numbers of tiny ...
sensor chip. Since the first commercial optical mouse, the IntelliMouse introduced in 1999, most optical mouse devices use CMOS sensors. In February 2018, researchers at
Dartmouth College Dartmouth College (; ) is a private research university in Hanover, New Hampshire. Established in 1769 by Eleazar Wheelock, it is one of the nine colonial colleges chartered before the American Revolution. Although founded to educate Native ...
announced a new image sensing technology that the researchers call QIS, for Quanta Image Sensor. Instead of pixels, QIS chips have what the researchers call "jots." Each jot can detect a single particle of light, called a
photon A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless, so they alwa ...
.


See also

* List of sensors used in digital cameras *
Contact image sensor Contact image sensors (CIS) are image sensors used in flatbed scanners almost in direct contact with the object to be scanned. Charge-coupled devices (CCDs), the other kind of sensor often used in scanners, use mirrors to bounce light to a stati ...
(CIS) * Electro-optical sensor * Video camera tube *
Semiconductor detector A semiconductor detector in ionizing radiation detection physics is a device that uses a semiconductor (usually silicon or germanium) to measure the effect of incident charged particles or photons. Semiconductor detectors find broad applicat ...
* Fill factor * Full-frame digital SLR *
Image resolution Image resolution is the detail an image holds. The term applies to digital images, film images, and other types of images. "Higher resolution" means more image detail. Image resolution can be measured in various ways. Resolution quantifies how ...
* Image sensor format, the sizes and shapes of common image sensors * Color filter array, mosaic of tiny color filters over color image sensors * Sensitometry, the scientific study of light-sensitive materials * History of television, the development of electronic imaging technology since the 1880s *
List of large sensor interchangeable-lens video cameras List of digital video cameras with an image sensor larger than 2/3 inch and producing video in a horizontal resolution equal or higher than 1920 pixels. Digital video cameras Still cameras with video mode See also * List of 4K video re ...
*
Oversampled binary image sensor An oversampled binary image sensor is an image sensor with non-linear response capabilities reminiscent of traditional photographic film. Each pixel in the sensor has a binary response, giving only a one-bit quantized measurement of the local light ...
*
Computer vision Computer vision is an interdisciplinary scientific field that deals with how computers can gain high-level understanding from digital images or videos. From the perspective of engineering, it seeks to understand and automate tasks that the human ...
*
Push broom scanner A push broom scanner, also known as an along-track scanner, is a device for obtaining images with spectroscopic sensors. The scanners are regularly used for passive remote sensing from space, and in spectral analysis on production lines, for exampl ...
* Whisk broom scanner


References


External links


Digital Camera Sensor Performance Summary
by Roger Clark * (with graphical buckets and rainwater analogies) {{Authority control Digital photography MOSFETs