Scanning systems

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. The most common type of scanner used in offices and in the home is the flatbed scanner, where the document is placed on a glass window for scanning. A sheetfed scanner, which moves the page across an image sensor using a series of rollers, may be used to scan one document at a time or multiple, as in an automatic document feeder. A handheld scanner is a portable version of an image scanner that can be used on any flat surface. Scans are usually downloaded to the computer that the scanner is connected to, although some scanners are able to store scans on standalone flash media (e.g., memory cards and USB drives). Modern scanners typically use a charge-coupled device (CCD) or a contact image sensor (CIS) as the image sensor, whereas drum scanners, developed earlier and still used for the highest possible image quality, use a photomultiplier tube (PMT) as the image sensor. Document cameras, which use commodity or specialized high-resolution cameras, photograph documents all at once.