Part of what determines the overall quality of a scanned image is the method by which a scanner collects data. Unlike other kinds of scanners, flatbed scanners use two different approaches. One is charge-coupled devices, or CCDs, and the other is contact image sensors, or CIS.

Charge-coupled devices are tiny light-sensitive semiconductor chips that consist of an array of light-sensitive photocells. CCD scanners pass a light source over a document on the scanning bed and use a system of mirrors and a lens to focus the image on the chip. CIS scanners, on the other hand, replace the chips, mirror and lens with a single row of sensors placed extremely close to the document. The result is a scanner that is thinner and cheaper than traditional CCD scanners but not yet as good in resolution, image quality and color fidelity.