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Contact image sensors (CIS) are image sensors used in flatbed scanners almost in direct contact with the object to be scanned. 
A CIS typically consists of a linear array of detectors, covered by focusing lenses and flanked by red, green, and blue LEDs for illumination. The use of LEDs allows the CIS to be highly power efficient, allowing scanners to be powered through the minimal line voltage supplied via a
Contact image sensors (CIS) are image sensors used in flatbed scanners almost in direct contact with the object to be scanned. Charge-coupled device
A charge-coupled device (CCD) is an integrated circuit containing an array of linked, or coupled, capacitors. Under the control of an external circuit, each capacitor can transfer its electric charge to a neighboring capacitor. CCD sensors are a ...
s (CCDs), the other kind of sensor often used in scanners, use mirrors to bounce light to a stationary sensor. Scanners using CISs are much smaller than ones that use CCDs, use typically a tenth as much power, and are particularly suitable for low power and portable applications, often powered over USB
Universal Serial Bus (USB) is an industry standard, developed by USB Implementers Forum (USB-IF), for digital data transmission and power delivery between many types of electronics. It specifies the architecture, in particular the physical ...
.
A CIS typically consists of a linear array of detectors, covered by focusing lenses and flanked by red, green, and blue LEDs for illumination. The use of LEDs allows the CIS to be highly power efficient, allowing scanners to be powered through the minimal line voltage supplied via a USB
Universal Serial Bus (USB) is an industry standard, developed by USB Implementers Forum (USB-IF), for digital data transmission and power delivery between many types of electronics. It specifies the architecture, in particular the physical ...
connection. CIS devices typically produce lower image quality compared to CCD devices; in particular, the depth of field
The depth of field (DOF) is the distance between the nearest and the farthest objects that are in acceptably sharp focus (optics), focus in an image captured with a camera. See also the closely related depth of focus.
Factors affecting depth ...
is greatly limited, which poses a problem for material that is not perfectly flat. However, a CIS contact sensor is smaller and lighter than a CCD line sensor, and allows all the necessary optical elements to be included in a compact module, thus helping to simplify the inner structure of the scanner. With a CIS contact sensor, the scanner can be portable, with a height of only around 30 mm.
CIS is a key component widely used in scanners (especially portable scanners), electrographs, bar code readers and optical identification technology.
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