How Does a Flatbed Scanner Operate?

Parts of a Flatbed Scanner

A flatbed scanner is connected directly to a computer or piggybacked onto a computer printer. The connection can be by standard parallel port, USB, SCSI, or FireWire interface. Under the lid of the flatbed scanner is a transparent glass pane. Inside the scanner is a moving light source and other electronics. There are no user-serviceable parts inside a scanner. Depending on the particular model, there may be buttons on the front of the scanner, or it may operate strictly through its software. To communicate useful data to the computer, most scanners use the TWAIN protocol. TWAIN stands for "technology without an interesting name."

Depending on the size of the original document and the resolution and magnification selected, a scan can consist of many megabytes of data. Resolution is measured in dots per inch (dpi). A color scan produces a much larger file than the equivalent scan in black and white. To make your first scan, open an art program or the scanner's native software. Select the minimum resolution you believe will produce a usable scan. Place the original document face down on the glass and close the lid, then start the scan. Most scanners have a preview mode, which produces a quick image of what the final scan will look like. If the preview is acceptable, make the final scan. This can take a few minutes, while the light source moves slowly up and down the length of the scanner, translating the data from the image into a file that can be stored on the computer's hard drive. Scanners typically make files in the .jpg format. Some can also create files in .bmp, .tif or other formats. Last, save the file to your computer and open it with an art program. With the addition of OCR, or optical character recognition scanner software, you can scan documents and avoid retyping. Even with perfectly legible originals, OCR scanning of documents is not 100 percent accurate, and the documents will need to be proofread and corrected.

If a black and white scan of a document is too small to read, increase the resolution to 600 dpi or above. Use the scanning software's crop function to make the area to be scanned as small as possible. This saves time and megabytes.