An image sensor or imaging sensor is a sensor that detects and conveys the information that constitutes an image. It does so by converting the variable attenuation of light waves (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. Image sensors are used
A CCD image sensor on a flexible circuit board
in electronic imaging devices of both analog and digital types, which include digital cameras, camera modules, medical imaging equipment, night vision equipment such as thermal imaging devices, radar, sonar, and others. As technology changes, digital imaging tends to replace analog imaging.
Early analog sensors for visible light were video camera tubes. Currently, used types are semiconductor charge-coupled devices (CCD) or active pixel sensors in complementary metal–oxide–semiconductor (CMOS) or N-type metal-oxide-semiconductor (NMOS, Live MOS) technologies. Analog sensors for invisible radiation tend to involve vacuum tubes of various kinds. Digital sensors include flat panel detectors.
CCD vs CMOS technology
Today, most digital cameras use a CMOS sensor, because CMOS sensors perform better than CCDs. An example is the fact that they incorporate an integrated circuit, helping reduce costs. CCD is still in use for cheap low entry cameras, but weak in burst mode. 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. 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 amplifier(s), filling the empty line closest to the amplifiers(s). 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 be detected. Some CMOS imaging
A micrograph of the corner of the photosensor array of a ‘webcam’ digital camera
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 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 arrays and now adapted to silicon-based detector technology. Another approach is to utilize the very fine dimensions available in modern CMOS technology to implement a CCD like structure entirely in CMOS technology. This can be achieved by separating individual poly-silicon gates by a very small gap. These hybrid sensors are still in the research phase and can potentially harness the benefits of both CCD and CMOS imagers.
See also: EMVA1288
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 size increases.
There are several main types of color image sensors, differing by the type of color-separation mechanism:
Image sensor on the motherboard of a Nikon Coolpix L2 6 MP
- Bayer filter sensor, low-cost and most common, using a color filter array that passes red, green, or blue light to selected pixel sensors, forming interlaced grids sensitive to red, green, and blue – the missing color samples are interpolated using a demosaicing algorithm. In order to avoid interpolated color information, techniques like color co-site sampling use a piezo mechanism to shift the color sensor in pixel steps. The Bayer filter sensors also include back-illuminated sensors, where the light enters the sensitive silicon from the opposite side of where the transistors and metal wires are, such that the metal connections on the devices side are not an obstacle for the light, and the efficiency is higher.
- 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.
- 3CCD, using three discrete image sensors, with the color separation done by a dichroic prism.
Special sensors are used in various applications such as thermography, creation of multi-spectral images, video laryngoscopes, gamma cameras, sensor arrays for x-rays, and other highly sensitive arrays for astronomy.
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.
Bayer pattern on sensor
Foveon's scheme of vertical filtering for color sensing
Sensors used in digital cameras
|Width (px)||Height (px)||Aspect ratio||Actual pixel count||Megapixels||Camera examples|
|100||100||1:1||10,000||0.01||Kodak (by Steven Sasson) Prototype (1975)|
|640||480||4:3||307,200||0.3||Apple QuickTake 100 (1994)|
|832||608||4:3||505,856||0.5||Canon Powershot 600 (1996)|
|1,024||768||4:3||786,432||0.8||Olympus D-300L (1996)|
|1024||1024||1,048,576||1.0||Nikon NASA F4 (1991)|
|1,280||960||4:3||1,228,800||1.3||Fujifilm DS-300 (1997)|
|1,280||1,024||5:4||1,310,720||1.3||Fujifilm MX-700, Fujifilm MX-1700 (1999), Leica Digilux (1998), Leica Digilux Zoom (2000)|
|1,600||1,200||4:3||1,920,000||2||Nikon Coolpix 950, Samsung GT-S3500|
|2,048||1,536||4:3||3,145,728||3||Canon PowerShot A75, Nikon Coolpix 995|
|2,272||1,704||4:3||3,871,488||4||Olympus Stylus 410, Contax i4R (although CCD is actually square 2,272×2,272)|
|2,560||1,920||4:3||4,915,200||5||Olympus E-1, Sony Cyber-shot DSC-F707, Sony Cyber-shot DSC-F717|
|2,816||2,112||4:3||5,947,392||5.9||Olympus Stylus 600 Digital|
|3,008||2,000||3:2||6,016,000||6||D100, Nikon D40, D50, D70, D70s, Pentax K100D, Konica Minolta Maxxum 7D, Konica Minolta Maxxum 5D, Epson R-D1|
|3,072||2,048||3:2||6,291,456||6.3||Canon EOS 10D, Canon EOS 300D|
|3,072||2,304||4:3||7,077,888||7||Olympus FE-210, Canon PowerShot A620|
|3,456||2,304||3:2||7,962,624||8||Canon EOS 350D|
|3,264||2,448||4:3||7,990,272||8||Olympus E-500, Olympus SP-350, Canon PowerShot A720 IS, Nokia 701, HTC Desire HD, Apple iPhone 4S|
|3,504||2,336||3:2||8,185,344||8.2||Canon EOS 30D, Canon EOS-1D Mark II, Canon EOS-1D Mark II N|
|3,520||2,344||3:2||8,250,880||8.25||Canon EOS 20D|
|3,648||2,736||4:3||9,980,928||10||Canon PowerShot G11, Canon PowerShot G12, Canon PowerShot S90, Canon PowerShot S95, Nikon CoolPix P7000, Nikon CoolPix P7100, Olympus E-410, Olympus E-510, Panasonic FZ50, Fujifilm FinePix HS10, Samsung EX1|
|3,872||2,592||3:2||10,036,224||10||Nikon D40x, Nikon D60, Nikon D3000, Nikon D200, Nikon D80, Pentax K10D, Pentax K200D, Sony DSLR-A100|
|3,888||2,592||3:2||10,077,696||10.1||Canon EOS 40D, Canon EOS 400D, Canon EOS 1000D|
|4,000||3,000||4:3||12,000,000||12||Canon Powershot G9, Fujifilm FinePix S200EXR, Nikon Coolpix L110, Kodak Easyshare Max Z990|
|4,256||2,832||3:2||12,052,992||12.1||Nikon D3, Nikon D3S, Nikon D700, Fujifilm FinePix S5 Pro|
|4,272||2,848||3:2||12,166,656||12.2||Canon EOS 450D|
|4,032||3,024||4:3||12,192,768||12.2||Olympus PEN E-P1|
|4,288||2,848||3:2||12,212,224||12.2||Nikon D2Xs/D2X, Nikon D300, Nikon D300S, Nikon D90, Nikon D5000, Pentax K-x|
|4,900||2,580||16:9||12,642,000||12.6||RED ONE Mysterium|
|4,368||2,912||3:2||12,719,616||12.7||Canon EOS 5D|
|7,920 (2,640 × 3)||1,760||3:2||13,939,200||13.9||Sigma SD14, Sigma DP1 (3 layers of pixels, 4.7 MP per layer, in Foveon X3 sensor)|
|4,672||3,104||3:2||14,501,888||14.5||Pentax K20D, Pentax K-7|
|4,752||3,168||3:2||15,054,336||15.1||Canon EOS 50D, Canon EOS 500D, Sigma SD1|
|4,896||3,264||3:2||15,980,544||16.0||Canon EOS 1D Mark IV, Fujifilm X-Pro1, Fujifilm X-E1 (X-Trans sensor has a different pattern to a Bayer sensor)|
|4,928||3,264||3:2||16,075,136||16.1||Nikon D7000, Nikon D5100, Pentax K-5|
|4,992||3,328||3:2||16,613,376||16.6||Canon EOS-1Ds Mark II|
|5,184||3,456||3:2||17,915,904||17.9||Canon EOS 1D X, Canon EOS 7D, Canon EOS 60D, Canon EOS 100D, Canon EOS 550D, Canon EOS 600D, Canon EOS 650D, Canon EOS 700D|
|5,270||3,516||3:2||18,529,320||18.5||Leica M9, RED Dragon|
|5,472||3,648||3:2||19,961,856||19,9||Canon EOS-1D X Mark II, Canon EOS 6D, Canon EOS 7D Mark II, Canon EOS 70D|
|5,616||3,744||3:2||21,026,304||21.0||Canon EOS-1Ds Mark III, Canon EOS-5D Mark II|
|5,760||3,840||3:2||22,118,400||22,1||Canon EOS 5D Mark III|
|6,000||4,000||3:2||24,000,000||24||Canon EOS 80D, Canon EOS 750D, Canon EOS 760D|
|6,048||4,032||3:2||24,385,536||24.4||Sony α850, Sony α900, Sony α99, Nikon D3X and Nikon D600|
|5,140||5,140||1:1||26,419,600||26.4||Leica S1 (line scanner, 1997)|
|7,360||4,912||3:2||36,152,320||36.2||Nikon D800, Sony α7R|
|7,320||5,484||4:3||40,142,880||40.1||Phase One IQ140|
|7,728||5,368||~10:7||41,483,904||41.5||Nokia 808 PureView|
|8,176||6,132||4:3||50,135,232||50.1||Hasselblad H3DII-50, Hasselblad H4D-50|
|8,688||5,792||3:2||50,320,896||50,3||Canon EOS 5DS / 5DS R|
|11,250||5,000||9:4||56,250,000||56.3||Better Light 4000E-HS (scanned)|
|8,984||6,732||4:3||60,480,288||60.5||Phase One IQ160, Phase One P65+|
|10,320||7,752||4:3||80,000,640||80||Leaf Aptus-II 12, Leaf Aptus-II 12R|
|10,328||7,760||4:3||80,145,280||80.1||Phase One IQ180|
|9,372||9,372||1:1||87,834,384||87.8||Leica RC30 (point scanner)|
|12,600||10,500||6:5||132,300,000||132.3||Phase One PowerPhase FX/FX+ (line scanner)|
|18,000||8,000||9:4||144,000,000||144||Better Light 6000-HS/6000E-HS (line scanner)|
|21,250||7,500||17:6||159,375,000||159.4||Seitz 6x17 Digital (line scanner)|
|16,352*||12,264*||4:3||200,540,928||200.5||Hasselblad H4D-200MS (*actuated multi (6x) shot)|
|18,000||12,000||4:3||216,000,000||216||Better Light Super 6K-HS (line scanner)|
|24,000||15,990||~ 3:2||383,760,000||383.8||Better Light Super 8K-HS (line scanner)|
|30,600||13,600||9:4||416,160,000||416.2||Better Light Super 10K-HS (line scanner)|
|62,830||7,500||~ 25:3||471,225,000||471.2||Seitz Roundshot D3 (80 mm lens) (scanned)|
|62,830||13,500||~ 5:1||848,205,000||848.2||Seitz Roundshot D3 (110 mm lens) (line scanner)|
|157,000||18,000||~ 26:3||2,826,000,000||2,826||Better Light 300 mm lens Digital (line scanner)|
Infrared view of the Orion Nebula taken by ESO's HAWK-I, a cryogenic wide-field imager.
The largest companies that manufacture imaging sensors include the following:
- Aptina (formerly division of Micron Technology) - Now part of ON Semiconductor
- Eastman Kodak
- ESS Technology
- OmniVision Technologies
- ON Semiconductor (formerly Cypress Semiconductor)
- Video camera tube
- Semiconductor detector
- Full-frame digital SLR
- 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
- Oversampled binary image sensor
- computer vision
- TJ Donegan. "Casio Exilim EX-H50 First Impressions Review". Retrieved February 23, 2015.
- Moynihan, Tom. "CMOS Is Winning the Camera Sensor Battle, and Here's Why". Retrieved 10 April 2015.
- scmos.com, home page
- ieee.org - CCD in CMOS Padmakumar R. Rao et al., "CCD structures implemented in standard 0.18 µm CMOS technology"
- semiconductor.net - Sony Backside Illuminated CMOS Image Sensor
- nikkeibp.co.jp - OmniVision on Backside-illuminated CMOS Sensors
- "Deepest Ever Look into Orion". Retrieved 13 July 2016.
- Steve Dent. "Sony's first 'curved sensor' photo may herald better images, cheaper lenses". Retrieved July 8, 2014.
- Digicam history 1997
- ON Semiconductor to Acquire Aptina Imaging
- ON Semiconductor to Acquire Truesense Imaging, Inc
- Digital Camera Sensor Performance Summary by Roger Clark.