A scanner is a device that can scan, analyze, and convert images of photos, printed documents, and handwritten documents, or small objects such as ornaments into digital images.
Most scanners are now variants of desktop scanners. Hand-held scanners were once popular; however, because it fails to obtain ideal image quality, it has now been eliminated. These scanners all use charge-coupled devices as image sensors, while drum scanners use photomultiplier tubes as image sensors. Scanners are very important in our daily lives are widely used. Other types of scanners, such as planetary scanners, which belong to book scanner, can shoot images for books and documents. The laser distance scanner can make a model of a three-dimensional space object. The multifunction printer (MFP) commonly used today integrates a scanner, printer, copier, and fax machine.
The scanner can usually read the red, green, and blue (RGB) 3 primary color data through the photosensitive CCD, process different exposure situations with some patented algorithms, and send the image data to the computer through the scanner's input/output interface. The transmission interface includes SCSI, USB, or parallel ports used earlier. The color depth would be determined by the characteristics of the CCD, usually at least 24 bits. Advanced models have 48 bit or higher.
Another indicator that affects image quality is the resolution of the image, measured in dots per hour (dpi), or more accurately measured in samples per inch. Scanner manufacturers usually prefer to advertise their products with interpolated resolution rather than true optical resolution. However, the interpolation resolution could be greatly improved by software interpolation, resulting in the illusion of exaggerated resolution. In 2004, a home-grade scanner can achieve an optical resolution of 1600–3200 dpi. High-end desktop scanners can scan at up to 5400 dpi, while drum scanners can achieve optical resolutions of 8000–14,000 dpi. Scanner manufacturers usually claim that the interpolation resolution can reach 19,200 dpi, but these numbers are meaningless, and the theoretically possible interpolation pixels are infinite.