Scanner is the main equipment for inputting words and pictures, which is equivalent to the eyes of a computer. It can convert optical signals into electrical signals through photoelectric devices, convert electrical signals into digital signals through analog-to-digital converters and transmit them to computers, and input a large number of words and pictures into computers.

The key device of scanner is charge coupler, which uses prism dichroic optical system to divide natural light into three primary colors of red, green and blue to scan graphics.

Flat scanner, text and pictures are fixed in a glass window, and the scanning head moves under the text or pictures to receive the light reflected by the text or pictures. These reflected lines are reflected by the mirror system, and the light is focused on the photodiode through the convex lens, which turns the light into current and finally converts it into digital information and stores it in the computer. It can scan and read a whole page of text or pictures at a time.

The performance indicators of the scanner include: optical resolution, color number, scanning speed and format size. Optical resolution is also called horizontal resolution, and the unit is pixel/inch or point/inch. The number of color bits is the scanner's ability to distinguish the color of a picture.