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An image sensor is a device that converts a visual image to an electric signal. It is used mostly used in digital cameras and other imaging devices. It is a set of charge-coupled devices (CCD) or CMOS sensors such as active-pixel sensors.
There are several main types of color image sensors, differing by the means of the color separation mechanism:
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. 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 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. 
There are a 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 a detailed guide to digital sensor performance, see Roger Clark's article.
Special sensors are used for various applications. The most important are the sensors for thermal imaging, creation of multi-spectral images, gamma cameras, sensor arrays for x-rays, IR Rays Infrared Rays and other highly sensitive arrays for astronomy.
Leading Suppliers of Image Sensors
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Image_sensor". A list of authors is available in Wikipedia.|