The principle of the scanner is actually very simple, is the same as we usually look in the mirror. When it scans the image (only one line at a time), the light is reflected back from the object, through the lens into the CCD (charge-coupled device). the CCD converts the light into an analog voltage signal, and mark each pixel's grayscale, and then by the ADC (analog-to-digital converter) will be converted from an analog voltage signal to a digital signal, each color using 8, 10, or 12-bit to indicate that the scanned image is saved in the computer through the Twain (a special format for scanned images) format. Twain (a special format for scanned images) format is saved in the computer.