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Image sensor

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A CCD image sensor on a flexible circuit board
Image sensor on the motherboard of a Nikon Coolpix L2 6MP

An image sensor is a device that converts an optical image to an electric signal. It is used mostly in digital cameras and other imaging devices. Early sensors were video camera tubes but a modern one is typically a charge-coupled device (CCD) or a complementary metal–oxide–semiconductor (CMOS) active pixel sensor.

CCD vs CMOS

Today, most digital still cameras use either a CCD image sensor or a CMOS sensor. Both types of sensor accomplish the same task of capturing light and converting it into electrical signals.

A CCD 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 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 the other hand, CCD sensors are more susceptible to vertical smear from bright light sources when the sensor is overloaded; high-end frame transfer CCDs in turn do not suffer from this problem.

CMOS can potentially be implemented with fewer components, use less power and/or provide faster readout than CCDs. CCD is a more mature technology and is in most respects the equal of CMOS.[1][2] 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.[3] 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-silcion gates by a very small gap. These hybrid sensors are still in the research phase, and can potentially harness the benefits of both the CCDs and the CMOS imagers.[4]

Performance

An infrared-blocking filter removed from a Canon EOS 350D DSLR.

There are many parameters that can be used to evaluate the performance of an image sensor, including its dynamic range, its signal-to-noise ratio, its low-light sensitivity, etc. For sensors of comparable types, the signal-to-noise ratio and dynamic range improve as the size increases.

Color sensors

There are several main types of color image sensors, differing by the means of the color separation mechanism:

  • Bayer 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 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.[3][4]
  • 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. Considered the best quality, and generally more expensive than single-CCD sensors.

Sensors used in digital cameras

Width Height Aspect ratio Actual pixel count Megapixels Camera examples
320 240 4:3 aspect ratio 76,800 0.07 Steven Sasson Prototype (1975)
640 480 4:3 aspect ratio 307,200 0.3 Apple QuickTake 100 (1994)
832 608 4:3 aspect ratio 505,856 0.5 Canon Powershot 600 (1996)
1,024 768 4:3 aspect ratio 786,432 0.8 Olympus D-300L (1996)
1,280 960 4:3 aspect ratio 1,228,800 1.3 Fujifilm DS-300 (1997)
1,280 1,024 5:4 1,310,720 1.3 Fujifilm MX-700 / Leica Digilux (1998), Fujifilm MX-1700 (1999) / Leica Digilux Zoom (2000)
1,600 1,200 4:3 aspect ratio 1,920,000 2 Nikon Coolpix 950
1,600 1,200 4:3 aspect ratio 1,920,000 2 Samsung GT-S3500
2,012 1,324 3:2 aspect ratio 2,663,888 2.74 Nikon D1
2,048 1,536 4:3 aspect ratio 3,145,728 3 Canon PowerShot A75, Nikon Coolpix 995
2,272 1,704 4:3 aspect ratio 3,871,488 4 Olympus Stylus 410, Contax i4R (although CCD is actually square 2,272x2,272)
2,464 1,648 3:2 aspect ratio 4,060,672 4.1 Canon 1D
2,560 1,920 4:3 aspect ratio 4,915,200 5 Olympus E-1, Sony Cyber-shot DSC-F707, Sony Cyber-shot DSC-F717
2,816 2,112 4:3 aspect ratio 5,947,392 6 Olympus Stylus 600 Digital
3,008 2,000 3:2 aspect ratio 6,016,000 6 Nikon D40, D50, D70, D70s, Pentax K100D
3,072 2,048 3:2 aspect ratio 6,291,456 6.3 Canon 300D, Canon 10D
3,072 2,304 4:3 aspect ratio 7,077,888 7 Olympus FE-210, Canon PowerShot A620
3,456 2,304 3:2 aspect ratio 7,962,624 8 Canon 350D
3,264 2,448 4:3 aspect ratio 7,990,272 8 Olympus E-500, Olympus SP-350, Canon PowerShot A720 IS
3,504 2,336 3:2 aspect ratio 8,185,344 8.2 Canon 30D, Canon 1D II, Canon 1D II N
3,520 2,344 3:2 aspect ratio 8,250,880 8.25 Canon 20D
3,648 2,736 4:3 aspect ratio 9,980,928 10 Olympus E-410, Olympus E-510, Panasonic FZ50, Fujifilm FinePix HS10
3,872 2,592 3:2 aspect ratio 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 3:2 aspect ratio 10,077,696 10.1 Canon 400D, Canon 40D
4,064 2,704 3:2 aspect ratio 10,989,056 11 Canon 1Ds
4,000 3,000 4:3 aspect ratio 12,000,000 12 Canon Powershot G9, Fujifilm FinePix S200EXR
4,256 2,832 3:2 aspect ratio 12,052,992 12.1 Nikon D3, Nikon D3S, Nikon D700, Fujifilm FinePix S5 Pro
4,272 2,848 3:2 aspect ratio 12,166,656 12.2 Canon 450D
4,032 3,024 4:3 aspect ratio 12,192,768 12.2 Olympus PEN E-P1
4,288 2,848 3:2 aspect ratio 12,212,224 12.2 Nikon D2Xs/D2X, Nikon D300, 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 aspect ratio 12,719,616 12.7 Canon 5D
7,920 (2,640 × 3) 1,760 3:2 aspect ratio 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 aspect ratio 14,501,888 14.5 Pentax K20D, Pentax K-7
4,752 3,168 3:2 aspect ratio 15,054,336 15.1 Canon EOS 500D, Canon EOS 50D
4,928 3,262 3:2 aspect ratio 16,075,136 16.1 Nikon D7000, Pentax K-5
4,992 3,328 3:2 aspect ratio 16,613,376 16.6 Canon 1Ds II, Canon 1D Mark IV
5,184 3,456 3:2 aspect ratio 17,915,904 17.9 Canon EOS 550D, Canon EOS 60D, Canon EOS 7D
5,270 3,516 3:2 aspect ratio 18,529,320 18.5 Leica M9
5,616 3,744 3:2 aspect ratio 21,026,304 21.0 Canon 1Ds III, Canon 5D Mark II
6,048 4,032 3:2 aspect ratio 24,385,536 24.4 Sony α 850, Sony α 900, Nikon D3X
7,500 5,000 3:2 aspect ratio 37,500,000 37.5 Leica S2
7,212 5,142 4:3 aspect ratio 39,031,344 39.0 Hasselblad H3DII-39
7,216 5,412 4:3 aspect ratio 39,052,992 39.1 Leica RCD100
8,176 6,132 4:3 aspect ratio 50,135,232 50.1 Hasselblad H3DII-50
11,250 5,000 9:4 56,250,000 56.3 Better Light 4000E-HS
8,956 6,708 4:3 aspect ratio 60,076,848 60.1 Hasselblad H4D-60
8,984 6,732 4:3 aspect ratio 60,480,288 60.5 Phase One P65+
10,320 7,752 4:3 aspect ratio 80,000,640 80 Leaf Aptus-II 12
9,372 9,372 1:1 87,834,384 87.8 Leica RC30
12,600 10,500 6:5 132,300,000 132.3 Phase One PowerPhase FX/FX+
18,000 8,000 9:4 144,000,000 144 Better Light 6000-HS/6000E-HS
21,250 7,500 17:6 159,375,000 159.4 Seitz 6x17 Digital
18,000 12,000 3:2 aspect ratio 216,000,000 216 Better Light Super 6K-HS
24,000 15,990 2,400:1,599 383,760,000 383.8 Better Light Super 8K-HS
30,600 13,600 9:4 416,160,000 416.2 Better Light Super 10K-HS
62,830 7,500 6,283:750 471,225,000 471.2 Seitz Roundshot D3 (80 mm lens)
62,830 13,500 6,283:1,350 848,205,000 848.2 Seitz Roundshot D3 (110 mm lens)
38,000 38,000 1:1 1,444,000,000 1,444 Pan-STARRS PS1
157,000 18,000 157:18 2,826,000,000 2,826 Better Light 300 mm lens Digital

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.

Companies

The largest companies that manufacture imaging sensors include the following:

See also

References

  1. ^ CCD vs CMOS from Photonics Spectra 2001
  2. ^ Sensors By Vincent Bockaert
  3. ^ a b [1] Cite error: The named reference "test3" was defined multiple times with different content (see the help page).
  4. ^ a b CCD in CMOS Padmakumar R. Rao et al., "CCD structures implemented in standard 0.18 µm CMOS technology" Cite error: The named reference "test4" was defined multiple times with different content (see the help page).
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