A scanner is a device that optically scans images, printed
text, handwriting, or an object, and converts it to a digital image. Common
examples found in offices are variations of the desktop (or flatbed) scanner
where the document is placed on a glass window for scanning. Hand-held
scanners, where the device is moved by hand, have evolved from text scanning
"wands" to 3D scanners used for industrial design, reverse
engineering, test and measurement, orthotics, gaming and other applications.
Mechanically driven scanners that move the document are typically used for
large-format documents, where a flatbed design would be impractical.
Modern scanners typically use a charge-coupled device (CCD)
or a Contact Image Sensor (CIS) as the image sensor, whereas older drum
scanners use a photomultiplier tube as the image sensor. A rotary scanner, used
for high-speed document scanning, is another type of drum scanner, using a CCD
array instead of a photomultiplier. Other types of scanners are planetary
scanners, which take photographs of books and documents, and 3D scanners, for
producing three-dimensional models of objects.
Another category of scanner is digital camera scanners, which
are based on the concept of reprographic cameras. Due to increasing resolution
and new features such as anti-shake, digital cameras have become an attractive
alternative to regular scanners. While still having disadvantages compared to
traditional scanners (such as distortion, reflections, shadows, low contrast),
digital cameras offer advantages such as speed, portability, gentle digitizing
of thick documents without damaging the book spine. New scanning technologies
are combining 3D scanners with digital cameras to create full-color,
photo-realistic 3D models of objects.
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