In order to recognize vehicle license numbers in real time, a CCD (charge-coupled device) camera with electronic shutter and a hierarchical computer system with a general-purpose microprocessor and pipelined image processors have been developed. Much quicker extraction of the vehicle-license plate on the front-view image is realized by optimization of parameters using Taguchi's method. Distinct images outdoors can be obtained using a suitable control of the lens-diaphragm and continuous lighting via floodlight equipment. The results of field tests show that recognition rates of about 90% in the daytime and about 65% at night were attained. The processing time per vehicle is about 150 ms on average.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
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Kanayama et al. (2002) studied this question.