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 waves (as they pass through or reflect off objects) into signals, the small bursts of current that convey the information. The waves can be light or other electromagnetic radiation. Image sensors are used 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
Today, most digital still cameras use a CMOS sensor because CMOS sensor technology has leapfrogged CCDs in recent years. 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 are converted to voltage one pixel at a time as they are read from the chip. Additional circuitry in the camera converts the voltage into digital information.
A CMOS imaging chip is a type of active pixel sensor made using the CMOS semiconductor process. Extra circuitry next to each photo sensor converts the light energy to a voltage. Additional circuitry on the chip may be included to convert the voltage to digital data.
Neither technology has a clear advantage in image quality. On one hand, CCD sensors are more susceptible to vertical smear from bright light sources when the sensor is overloaded; high-end CMOS sensors in turn do not suffer from this problem. On the other hand, cheaper CMOS sensors are susceptible to undesired effects that come as a result of rolling shutter.
CMOS sensors can potentially be implemented with fewer components, use less power, and/or provide faster readout than CCD sensors. CCD is a more mature technology and is in most respects the equal of CMOS. CMOS sensors are less expensive to manufacture than CCD sensors.
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.
The newer sensor technology is Back-side illuminated CMOS (BSI-CMOS) which uses less electricity than traditional CMOS with better performance than CCD, so lower end cameras still use CCD sensors such as those implemented by Fujifilm in its Bridge cameras. CCD sensors are rarely used in new models, except for very high pixel count, big sensor cameras which still use CCDs.
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:
- 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.
Until now all digital cameras use a flat sensor, but in 2014 Sony has a prototype of a curved sensor which will reduce/eliminate Petzval field curvature that occurs with a flat sensor. Although it is a prototype design, it is possible the curved sensor will be implemented in Sony's new fixed lens camera at the end of 2014. 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.
Sensors used in digital cameras
Width (px) Height (px) Aspect ratio Actual pixel count Megapixels Camera examples 100 1001:1 10,000 0.01 Kodak (by Steven Sasson) Prototype (1975) 640 480 307,200 0.3 Apple QuickTake 100 (1994) 832 608 505,856 0.5 Canon Powershot 600 (1996) 1,024 768 786,432 0.8 Olympus D-300L (1996) 1024 10241:1 1,048,576 1.0 Nikon NASA F4 (1991) 1,280 960 1,228,800 1.3 Fujifilm DS-300 (1997) 1,280 1,0245:4 1,310,720 1.3 Fujifilm MX-700, Fujifilm MX-1700 (1999), Leica Digilux (1998), Leica Digilux Zoom (2000) 1,600 1,200 1,920,000 2 Nikon Coolpix 950, Samsung GT-S3500 2,012 1,324 2,663,888 2.74 Nikon D1 2,048 1,536 3,145,728 3 Canon PowerShot A75, Nikon Coolpix 995 2,272 1,704 3,871,488 4 Olympus Stylus 410, Contax i4R (although CCD is actually square 2,272×2,272) 2,464 1,648 4,060,672 4.1 Canon 1D 2,560 1,920 4,915,200 5 Olympus E-1, Sony Cyber-shot DSC-F707, Sony Cyber-shot DSC-F717 2,816 2,112 5,947,392 5.9 Olympus Stylus 600 Digital 3,008 2,000 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 6,291,456 6.3 Canon EOS 10D, Canon EOS 300D 3,072 2,304 7,077,888 7 Olympus FE-210, Canon PowerShot A620 3,456 2,304 7,962,624 8 Canon EOS 350D 3,264 2,448 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 8,185,344 8.2 Canon EOS 30D, Canon EOS-1D Mark II, Canon EOS-1D Mark II N 3,520 2,344 8,250,880 8.25 Canon EOS 20D 3,648 2,736 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 10,036,224 10 Nikon D40x, Nikon D60, Nikon D3000, Nikon D200, Nikon D80, Pentax K10D, Pentax K200D, Sony Alpha A100 3,888 2,592 10,077,696 10.1 Canon EOS 40D, Canon EOS 400D, Canon EOS 1000D 4,064 2,704 10,989,056 11 Canon EOS-1Ds 4,000 3,000 12,000,000 12 Canon Powershot G9, Fujifilm FinePix S200EXR, Nikon Coolpix L110, Kodak Easyshare Max Z990 4,256 2,832 12,052,992 12.1 Nikon D3, Nikon D3S, Nikon D700, Fujifilm FinePix S5 Pro 4,272 2,848 12,166,656 12.2 Canon EOS 450D 4,032 3,024 12,192,768 12.2 Olympus PEN E-P1 4,288 2,848 12,212,224 12.2 Nikon D2Xs/D2X, Nikon D300, Nikon D300S, Nikon D90, Nikon D5000, Pentax K-x 4,900 2,580 12,642,000 12.6 RED ONE Mysterium 4,368 2,912 12,719,616 12.7 Canon EOS 5D 5,120 2,700 13,824,000 13.8 RED Mysterium-X 7,920 (2,640 × 3) 1,760 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 14,501,888 14.5 Pentax K20D, Pentax K-7 4,752 3,168 15,054,336 15.1 Canon EOS 50D, Canon EOS 500D, Sigma SD1 4,896 3,264 15,980,544 16.0 Fujifilm X-Pro1, Fujifilm X-E1 (X-Trans sensor has a different pattern to a Bayer sensor) 4,928 3,262 16,075,136 16.1 Nikon D7000, Nikon D5100, Pentax K-5 4,992 3,328 16,613,376 16.6 Canon EOS-1Ds Mark II, Canon EOS-1D Mark IV 5,184 3,456 17,915,904 17.9 Canon EOS 7D, Canon EOS 60D, Canon EOS 600D, Canon EOS 550D, Canon EOS 650D, Canon EOS 700D 4,928 3,696 18,200,000 18.2 Sony HX20 5,270 3,516 18,529,320 18.5 Leica M9, RED Dragon 5,616 3,744 21,026,304 21.0 Canon EOS-1Ds Mark III, Canon EOS-5D Mark II 6,048 4,032 24,385,536 24.4 Sony α 850, Sony α 900, Sony Alpha 99, Nikon D3X and Nikon D600 5,140 5,1401:1 26,419,600 26.4 Leica S1 (line scanner, 1997) 7,360 4,912 36,152,320 36.2 Nikon D800, Sony Alpha 7R 7,500 5,000 37,500,000 37.5 Leica S2 7,212 5,142 39,031,344 39.0 Hasselblad H3DII-39 7,216 5,412 39,052,992 39.1 Leica RCD100 7,264 5,440 39,516,160 39.5 Pentax 645D 7,320 5,484 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 50,135,232 50.1 Hasselblad H3DII-50, Hasselblad H4D-50 11,250 5,000 9:4 56,250,000 56.3 Better Light 4000E-HS (scanned) 8,956 6,708 60,076,848 60.1 Hasselblad H4D-60 8,984 6,732 60,480,288 60.5 Phase One IQ160, Phase One P65+ 10,320 7,752 80,000,640 80 Leaf Aptus-II 12, Leaf Aptus-II 12R 10,328 7,760 80,145,280 80.1 Phase One IQ180 9,372 9,3721:1 87,834,384 87.8 Leica RC30 (point scanner) 12,600 10,5006:5 132,300,000 132.3 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* 200,540,928 200.5 Hasselblad H4D-200MS (*actuated multi (6x) shot) 18,000 12,000 216,000,000 216 Better Light Super 6K-HS (line scanner) 24,000 15,990 ~ 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) 38,000 38,0001:1 1,444,000,000 1,444 Pan-STARRS PS1 157,000 18,000 ~ 26:3 2,826,000,000 2,826 Better Light 300 mm lens Digital (line scanner)
|This section does not cite any references or sources. (September 2013)|
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
- MAZeT GmbH
- OmniVision Technologies
- ON Semiconductor (formerly Cypress Semiconductor)
- PixArt Imaging
- Town Line Technologies
- Trusense imaging - Now part of ON 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
- 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.
- dalsa.com - CCD vs CMOS from Photonics Spectra 2001
- dpreview.com - Sensors By Vincent Bockaert
- 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
- 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.