There was not sufficient time in this task to examine more than a few of the large number of scanners and digital cameras that are now commercially available. Therefore, we have selected four units for discussion that reasonably cover the range of configurations which the Smithsonian might consider for its document imaging activities. The third is a 35 mm color slide scanner. The CCD elements are spaced at intervals corresponding to the sampling frequency of 600 ppi on the original material. The glass scanning stage, which supports the document, also contains a white-reference board just outside of the area where the document is normally placed.
Every scan starts at the white-reference board.
Only the brightest reading for each of the CCD elements is retained. At this point, a dark reading and three bright color readings have been recorded for each CCD element. As the scanning table moves the original material over the fluorescent tubes and the CCD sensor, the dark and bright references are used to adjust the output of each CCD element. The Super Coolscan scans 35 mm mounted or unmounted slides, with a maximum sampling frequency of 2,700 ppi. It can produce a full 28 Mbyte file in less than 45 seconds.