The computer scanner is one of the most precise methods of converting printed material such as documents and photographs into computer readable form. Scanners surged in popularity with the desk top publishing revolution and have since become more readily available, the cheapest being the hand held scanner which is passed over the document. The more expensive flat bed scanner is similar in operation to a photocopier and can be found in both colour and black and white variants.
The document or photograph to be scanned is placed face down on a glass plate and the lid is closed. A head the full width of the scanner then moves slowly over the document. As it moves it shines light at the document, the reflected light is picked up by receptors mounted in the moving head. Due to the fact that dark areas reflect less light than light areas, the scanner is able to build an accurate digital image of the document via this variance in the reflected light. This digital image is passed to the computer for further processing.
Colour scanners require three lights, one red, one green and one blue to build a colour image of the scanned document. Using this three light technique the head only needs to scan the document once to build a full colour image, the electronics required in a colour scanner are more sophisticated than those of the black and white scanner in order to process the larger amounts of data produced by the digital colour image.
