How Does a Scanner Work?

A desktop scanner (flatbed scanner) usually consists of a glass pane, under which a very bright light (usually xenon or cold cathode fluorescent) illuminates the pane, and a moving charge-coupled device.

Color scanners generally consist of three rows of charge-coupled device elements with red, green, and blue filters. The media to be scanned (photos, articles, etc.) are placed face-down on the glass pane, the light turns on, and the charge-coupled device and light source move across the pane, "scanning" the entire area. An image (whatever was put face-down) is therefore visible to the charge-coupled device because of the light it reflects. Transparent images like film negatives do not work in this way, and require special accessories or dedicated models (film scanners) that illuminate them from the upper side.

Some scanner models (usually found in businesses) are equipped with an "automatic document feed" or ADF feature, which allows the user to stack multiple pages into a hopper. Then the pages are automatically fed individually into the scanner, similar to a copy machine. The charge-coupled device remains still during ADF scanning, while the pages are moved through the scanner by rollers at a steady rate. A separate collection hopper catches the pages after they are scanned.

Scanners always come with scanner software that enables the user to not only connect the scanner to a computer, but to manipulate and edit the scans as well. Generally, there are three main types of scanners sold in the consumer market. These types are:

Flatbed scanner – This is the most popular type of scanner. This design is the one that most likely pops in your head when you think of a computer scanner. It consists of a main scanning area—the bed—with a hinged lid on top. These scanners are ideal for copying media of varying size, from a small photo to a large newspaper page.

Portable scanner – Portable scanners (sometimes called handheld scanners) are designed to be easily carried with you throughout the workday. The most cutting-edge portable scanners today look like wands or large pens, and they just need to be "swiped" over the media you need to scan.

Slide scanner/ Film scanner – A film scanner and a slide scanner are sometimes the same thing. Just as the name implies, they are specially designed to scan film negatives or slides. Many photographers use these scanners instead of using a photo lab to reproduce negatives after processing. As mentioned, some scanners feature the ability to scan both slides and film, while others only scan one or the other.

More information on scanners