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Line Scan

Line scan camera acquire an image one line at a time rather than as an entire two-dimensional image.  These cameras us line scan imagers, which consist of a single line of pixels (or perhaps two or three parallel lines in color imagers) that is repeatedly read out.  In line scanning, the camera and the object being imaged must move relative to each other in a direction perpendicular to the pixel line on the image sensors.  It is best if the relative motion is constant but methods exist to compensate for some variation in motion.  

Line scanning has the advantage that there is no top or bottom to the images produced.  Essentially, they can go on forever.  This is especially useful for acquistion of very long images, of a roll of plastic to be inspected, for example.  Even if multiple scan of an item are required for full coverage as in the digitizing of large artwork, line scanning only produces seams in one direction to be matched.  

Because the exposure time for each line is very short, bright line lighting is usually required.  Special illuminators for this purpose are available.  Many line scan cameras offer sensor with taps along their lengrth to speed up the readout process.  Some cameras can offer line repetition rates in excess of 100 kHz.  Rates over 50 kHz are now fairly common.