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. Many compact digital still cameras can record Sound and moving Video as well as still Photograph. It is a set of charge-coupled devices (CCD) or CMOS sensors such as active-pixel sensors. A charge-coupled device ( CCD) is an analog Shift register, that enables the transportation of analog signals (electric charges through successive stages (capacitors Complementary metal–oxide–semiconductor ( CMOS) (pronounced "see-moss" siːmɔːs ˈsiːmɒs is a major class of Integrated circuits CMOS technology An active-pixel sensor (APS, also commonly written active pixel sensor, is an Image sensor consisting of an Integrated circuit containing an array of pixel
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CCD vs CMOS
Today, most digital still cameras use either a CCD images 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. A charge-coupled device ( CCD) is an analog Shift register, that enables the transportation of analog signals (electric charges through successive stages (capacitors 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. An active-pixel sensor (APS, also commonly written active pixel sensor, is an Image sensor consisting of an Integrated circuit containing an array of pixel Complementary metal–oxide–semiconductor ( CMOS) (pronounced "see-moss" siːmɔːs ˈsiːmɒs is a major class of Integrated circuits CMOS technology Extra circuitry next to each photo sensor converts the light energy to a voltage. Additional circuitry on the chip converts the voltage to digital data.
Neither technology has a clear advantage in image quality. CMOS can potentially be implemented with fewer components, use less power and provide data faster than CCDs. CCD is a more mature technology and is in most respects the equal of CMOS. [1][2]
Performance
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. Dynamic range is a term used frequently in numerous fields to describe the Ratio between the smallest and largest possible values of a changeable quantity such as in Sound Signal-to-noise ratio (often abbreviated SNR or S/N) is an Electrical engineering concept also used in other fields (such as scientific Measurements
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 Bayer filter that passes red, green, or blue light to selected sensels, or pixels, forming interlaced grids sensitive to red, green, and blue. Explanation Bryce Bayer's patent called the green photosensors luminance-sensitive elements and the red and blue ones chrominance-sensitive elements. The image is then interpolated using a demosaicing algorithm. A demosaicing Algorithm is a digital image process used to interpolate a complete image from the partial raw data received from the color-filtered
- Foveon X3 sensor, using an array of layered sensors where every pixel contains three stacked sensors sensitive to the individual colors. The Foveon X3 sensor is a CMOS Image sensor for digital cameras designed by Foveon Inc
- 3CCD, using three discrete image sensors, with the color separation done by a dichroic prism. Three-CCD or 3CCD is a term used to describe an imaging system employed by some still cameras Video cameras Telecine and Camcorders A dichroic prism is a prism that splits Light into two beams of differing Wavelength ( Colour) Considered the best quality, and generally more expensive than single-CCD sensors.
Specialty sensors
Special sensors are used for various applications such as thermal imaging, creation of multi-spectral images, gamma cameras, sensor arrays for x-rays, and other highly sensitive arrays for astronomy. wiki stranglesnakejpg|thumb|Thermographic image of a Snake held by a human]] Infrared Thermography, thermal imaging, or thermal video, is a type of Multi-spectral imaging is a technology originally developed for space-based imaging A gamma camera is a device used to image gamma radiation emitting radioisotopes a technique known as scintigraphy X-radiation (composed of X-rays) is a form of Electromagnetic radiation. Astronomy (from the Greek words astron (ἄστρον "star" and nomos (νόμος "law" is the scientific study
See also
- Video camera tube
- Semiconductor detector
- Contact Image Sensor (CIS)
- Image sensor format: discusses the sizes and shapes of common image sensors
References
- ^ CCD vs CMOS from Photonics Spectra 2001
- ^ Sensors By Vincent Bockaert
External links
- Digital Camera Sensor Performance Summary by Roger Clark. In older Video cameras before the mid to late 1980s a video camera tube or pickup tube was used instead of a Charge-coupled device (CCD A semiconductor detector is a device that uses a semiconductor (usually Silicon or Germanium) to detect 'Contact Image Sensors (CIS' are a relatively recent technological innovation in the field of optical flatbed scanners that are rapidly replacing CCDs in low power and portable In Digital photography, the image sensor format is the shape and size of the Image sensor.
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