A contact image sensor (CIS) scans materials in close proximity, rather than using mirrors to reflect light to an image sensor inside a device. In a flatbed scanner, for example, the image sensor is directly below the glass, as close as possible to the media in the scanner bed. These devices can be more efficient than older scanning techniques, but they also tend to produce images of a lower quality. The tradeoff may be acceptable with some scans and settings.
These devices include an array of light emitting diodes (LEDs) to illuminate the media, along with an optical head and a sensor to detect and record light. The contact image sensor provides scans at a one to one ratio, with no magnification of the image or other distortions. These life-size scans can include documents, three dimensional objects, and materials like textiles that may need to be evaluated with the assistance of a scanner.
This technology includes some advantages for manufacturers and users. It can be very compact, which is useful for mobile scanners and devices that need to fit in compact areas. It's also highly efficient and is usually less expensive to produce than similar products. The LEDs use less energy than other light sources and can be turned off and on between uses. Unlike scanners which use older forms of illumination, a device that uses a contact image sensor is ready for use immediately, and does not need to be warmed up.
The disadvantage is the lower image quality. Documents produced with a contact image sensor may have a narrower range of colors and a lower resolution. Three dimensional objects can also be more challenging to scan, as the device works best with materials in close proximity. Shadowing and other artifacts can develop in the image when the technician works with materials that do not lie flat against the scanning bed.
Product developers who focus on contact image sensor technology also work on ways to make the technology better. Increases in image quality are a topic of research at some companies that make contact image sensor heads and integrated devices. Like other technology, it can progress rapidly, and newer equipment tends to offer the most advantages to users. Consumers interested in the technology may want to research to determine what kinds of products are currently on the market, and when companies are likely to issue new releases that might be of better quality.