Video data signal digitization and correction system

摘要

An analog video data signal digitization and correction system scans a medium to produce video data signals representing images printed on the medium. Two reference quantities representing analog reference signals produced by scanning a densely printed image and an area of the medium having no printed image are used to establish the maximum and minimum values of a range of possible values for each video data signal. The analog video data signals are compared with this range and a corrected digital value obtained for each data signal depending on its position in the range. In generating the reference quantities each analog reference signal is converted into a digital reference signal dependent on the position of the analog signal in a range of possible values. For each analog reference signal only a portion of the range of possible values is selected in order to increase the accuracy of the corresponding digital reference signal. The number of bits in the digital reference signal is kept low but the accuracy of each digital reference signal remains high. In converting each digital reference signal into an analog reference quantity additional high order bits are added to the digital reference signal so that each analog reference quantity has the same accuracy as its corresponding digital reference signal.