Image sensor

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.[1] 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.[2]

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.[3] 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.[4] 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.[5] 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.[6]

Performance

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.

Color separation

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.[7][8]
•     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.

Specialty sensors

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.^{[citation needed]}

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.^[10]

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
2,012	1,324	3:2	2,663,888	2.74	Nikon D1
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)
2,464	1,648	3:2	4,060,672	4.1	Canon 1D
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
4,064	2,704	3:2	10,989,056	11	Canon EOS-1Ds
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
5,120	2,700	16:9	13,824,000	13.8	RED Mysterium-X
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
4,080	4,080	1:1	16,646,400	16.6	Hasselblad 503CWD
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
4,928	3,696	4:3	18,200,000	18.2	Sony DSC-HX20
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)[11]
7,360	4,912	3:2	36,152,320	36.2	Nikon D800, Sony α7R
7,500	5,000	3:2	37,500,000	37.5	Leica S2
7,212	5,142	4:3	39,031,344	39.0	Hasselblad H3DII-39
7,216	5,412	4:3	39,052,992	39.1	Leica RCD100
7,264	5,440	4:3	39,516,160	39.5	Pentax 645D
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)
8,956	6,708	4:3	60,076,848	60.1	Hasselblad H4D-60
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)
38,000	38,000	1:1	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)

Infrared view of the Orion Nebula taken by ESO's HAWK-I, a cryogenic wide-field imager.^[9]

Companies

The largest companies that manufacture imaging sensors include the following:

• Agilent
• Aptina (formerly division of Micron Technology) - Now part of ON Semiconductor^[12]
• Canesta
• Canon
• Dalsa
• Eastman Kodak
• ESS Technology
• Fujifilm
• Matsushita
• Mitsubishi
• Nikon
• OmniVision Technologies
• ON Semiconductor (formerly Cypress Semiconductor)^[13]
• Samsung
• Sharp
• Sony
• STMicroelectronics
• Toshiba
• TowerJazz

See also

• 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

References

1. TJ Donegan. "Casio Exilim EX-H50 First Impressions Review". Retrieved February 23, 2015.
2. http://cpn.canon-europe.com/content/education/infobank/capturing_the_ima...
3. http://cpn.canon-europe.com/content/education/infobank/capturing_the_ima...
4. Moynihan, Tom. "CMOS Is Winning the Camera Sensor Battle, and Here's Why". Retrieved 10 April 2015.
5. scmos.com, home page
6. ieee.org - CCD in CMOS Padmakumar R. Rao et al., "CCD structures implemented in standard 0.18 µm CMOS technology"
7. semiconductor.net - Sony Backside Illuminated CMOS Image Sensor
8. nikkeibp.co.jp - OmniVision on Backside-illuminated CMOS Sensors
9. "Deepest Ever Look into Orion". Retrieved 13 July 2016.
10. Steve Dent. "Sony's first 'curved sensor' photo may herald better images, cheaper lenses". Retrieved July 8, 2014.
11. Digicam history 1997
12. ON Semiconductor to Acquire Aptina Imaging
13. ON Semiconductor to Acquire Truesense Imaging, Inc

External links

• Digital Camera Sensor Performance Summary by Roger Clark.