How a Scanner Works


Tutorial Home >Hardware >Peripherals >Scanners >How do I learn how a scanner scans content into my computer?
Tutorial Home >Hardware >Peripherals >Scanners >Installing a Scanner >How a Scanner Works

  Step 1:  Image

The process begins by placing an image face down on a glass window in the scanner. Beneath the glass window is a light source and a scanning mechanism—the scan head.
  Step 2:  Scan Head

As light bounces off the page from the light source, the scan head moves by means of a small motor beneath the glass. As the scan head moves, it captures the light that bounces off the page. The head can read very small portions of the page-less than 1/90,000th of a square inch.
  Step 3:  Mirrors

The light captured by the scan head is bounced through a set of mirrors inside the scanner. These mirrors constantly shift their position so that the light aligns with a scanner lens.
  Step 4:  Diodes

The scanner lens focuses the light onto devices called diodes. These diodes translate light into electrical current. As the strength of the light changes, so does the strength of the electrical current. When there is more light, the voltage is greater; when there's less light, the voltage is less.
  Step 5:  Analog-to-Digital Converter

A device called an analog-to-digital converter (ADC) reads this constantly changing stream of electrical voltage. It converts this analog stream into a series of thousands of digital pixels. Depending on the resolution of the scanner, it creates from 300 to 1,200 pixels per inch. In a color scanner, light is first directed through red, green, or blue filters before hitting the image being scanned.
  Step 6:  PC Connection

The pixels are sent to the PC via one of a variety of physical connections. Some scanners are connected via the parallel port, others via a USB port, and still others via a SCSI connection. No matter what connection is used, the data is stored on the PC in a digital format.