Image sensor

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:

• 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. The image is then interpolated using a demosaicing algorithm.

• Foveon X3 sensor, using an array of layered sensors where every pixel contains three stacked sensors sensitive to the individual colors.

• 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.

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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. 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.^{[1] [2]}

Performance

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.

Specialty sensors

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.

See also

• Video camera tube
• Semiconductor detector
• Contact Image Sensor (CIS)
• Charge-coupled device (CCD)
• Active pixel sensor (MOS, CMOS)
• Image sensor format: discusses the sizes and shapes of common image sensors

References

Leading Suppliers of Image Sensors

• OmniVision Technologies, Inc.
• Panavision SVI
• TOSHIBA Semiconductor Company - Click "Products/Imaging Solutions"
• STMicroelectronics Imaging Division
• Micron Technology, IncCMOS Image Sensors
• Galaxy Core, Inc CMOS Image Sensors