In computing, an image scanner—often abbreviated to just 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, 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 and 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.
In the biomedical research area, detection devices for DNA microarrays are called scanners as well. These scanners are high-resolution systems (up to 1 µm/ pixel), similar to microscopes. The detection is done via CCD or a photomultiplier tube (PMT).
Scanners are input devices which are capable of recognizing marks or characters. They are capable of entering information directly from the computer without the user keying it in. They are fast and accurate. the two major types of scanners are OCR (Optical character Reader) and MICR (Magnetic Ink character Reader)
OCR (Optical Character Reader)
These scanners are capable of detecting alphabetic and numeric characters. If the characters are handwritten, they should be of standard size and there should be no stylish loops in the letters and lines. The characters should be properly connected if hand-written or in characters of a special font called OCR, if typed. OCR devices examine each character as if they were made up of a collection of minute spots.
OMR (Optical Mark Reader)
These scanners are capable of recognizing a pen or pencil mark made on a paper. An OMR scanner can sense the presence and absence of a mark. When you appear in objective-type tests or examinations in future, where you have to mark your answers by filling up a square box or a circular shape with a pencil, out of all the square/circular shapes provided, to indicate your choice of answer - you will know that these types of answer sheets are to be fed directly in to the computer to be scanned by an OMR.
MICR (Magnetic Ink character Reader)
MICR was developed to assist the banking industry to process a large number of cheques everyday. The bank identification code and the customer's account number are pre-printed with a special ink on every cheque. the ink contains magnetizable particles of iron oxide. a magnetic ink character reader reads these characters by examining their shapes with the help of a matrix, and sends this information to the system.