Image scanners are commonly used for scanning documents into computers. The most commonly used scanners are flatbed scanners. Flat bed scanners are widely used today as a
computer peripheral equipment for scanning documents, books and pictures and for furnishing the scanned information to a
computer to be processed. A flatbed scanner is capable of converting the printed data on a document into digital form for processing by the computer. A typical flatbed scanner may include illumination and optical systems to accomplish scanning of the object. A document to be scanned or exposed is placed face down on a platen window, while a movable scan head moves over the document and to make a scan that converts the printed data on the document into digital form. The scan head is optically coupled to a linear array of light-sensing cells as
CCD or CIS cells, each cell corresponding to a pixel in the scanned image. The document that is to be scanned is fixedly placed on a transparent glass plate on the flat bed scanner. The transparent glass plate is rectangular-shaped with a size larger than the document that is to be scanned. Reference marks are provided on the transparent glass plate that allow the user to place the document at correct positions.
