Contact Image Sensor
Contact Image Sensor (CIS) (German as contact image sensor ) is an affordable, on CMOS -based technology for image sensors . CIS technology was mainly used for fax machines , but for some years it has been used increasingly for scanners in the lower price and quality categories. The manufacturer Canon calls this technique "LiDE": L ED i n d irect e xposure.
CIS are usually in the form of a line sensor (in contrast to area sensors in digital cameras, for example ), i.e. several thousand light-sensitive points are in a row. There is a tiny plastic lens on each of these points . The lighting is mostly done via LEDs attached parallel to the sensors - with color scanners via RGB LEDs. In order to capture images, the sensor needs almost direct contact with the original - hence the name.
The advantage of the CIS scanners compared to the established CCD scanners is the significantly lower overall height and the more cost-effective construction due to the elimination of complex optics as well as the lower power consumption, which could sometimes be reduced so that USB devices can be supplied with power directly via the USB cable can be supplied.
The disadvantage of the technology is the extremely shallow depth of field . In the case of originals that do not lie flat (e.g. folds in documents or book creases), blurring quickly occurs . Another disadvantage is a sometimes high level of image noise , which, however, is directly related to the manufacturing quality of the sensors.