Scanner Imaging TechnologyExplains the difference between CCD (Charged Coupled Device) imaging technology and CIS (Contact Image Sensor) technology used in large format scanners.
CCD vs. CIS Imaging Technology
CCD Imaging (Charged Coupled Device):
This method of scanning involves capturing images through the use of a series of cameras that are spread out across the scanning area. These scanning systems use a fluorescent light source and a series of mirrors to reflect light from the surface of the document and pass it to the camera array. The number of cameras will vary depending on brand, model, and scanner width. These systems are also very sensitive, and require calibration from time to time as atmospheric and environmental factors can throw the camera alignment off. The main calibration that needs to be performed is a stitching calibration which aligns the areas where camera fields intersect. Color and white point calibrations generally required for these scanners as well.
CIS Imaging ( Contact Image Sensor):
This method of scanning involves capturing images through the use of light reflected off of the surface of the document on to a silicone light sensing array. The silicone sensors are divided into individual sensing cells, and the size and density of these cells determines the optical DPI of the Scanner. The illumination for these Scanners is produced by Light Emitting Diodes (LED) pulses that are directed along surface of the document, and then on to the sensor. Color CIS sensing is produced by rapidly pulsing red, green and blue LEDs. Because there is no color filter used, the color gamut (range of the color spectrum that the scanner can capture), is generally somewhat less than that of a CCD scanner. One big advantage to these Scanners is that they do not require a warm up period like CCD scanners do.
Which Technology is right for me?
This question is somewhat dependent upon the application that the scanner is being used for. A good way to make this determination is whether you need to capture color at a high resolution and with a wide and highly accurate color gamut. If you really need high end graphics resolution, then a CCD Scanner is what you should be looking at. If you primarily scan line drawings, blueprints, or any other document that does not require high end graphics resolution, then you may want to consider a CIS Scanner. CIS Scanners require less calibration, will maintain calibration longer, are very effective and accurate machines for most scanning applications.
Explains the difference between true DPI (dots per inch) and interpolated DPI ratings.