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5 September 2002 Applications of small optical correlator in traffic
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A small optical correlator has been developed with shortened optical architecture and spatial folded architecture by means of design of new specified two FT lenses, which is fully controlled by Windows-based software. A hybrid real-time pattern recognition system comes into being, since it integrates the programmability, flexibility and accuracy of electronic computer to the rapidness, huge information and parallelism of optics. The small optical correlator overcomes the disadvantages of complex structure, bulkiness and resort to optical platform. It not only possesses such good performances as small bulk, vibration strength and high discrimination, but also can easily be switched between VanderLugt and joint transform operation due to its convenient disassociation. Compared with Vander Lugt correlator, joint transform correlator offers many advantages, such as no complex filter fabrication and stringent alignment problems, flexible structure, easy realization of correlation and suitability for real-time implementation. So in the article, the small optical correlator is used as one-armed JTC to study in two applications: license plate recognition and license plate supervision. Two methods are used to recognize license plate in JTC. One is feature-extracted preprocess, joint power spectrum subtraction and adaptive threshold; the other is data fusion and Lagrange multiplier. Meanwhile, considering the traits of CCD and framer, the program is optimally designed to make JTC system work on line. License plate supervision can be realized by choosing correlation threshold. License plate recognition and supervision are able to be switched by a shortcut key in C++ Builder. Computer simulation results and optical experiment results have been presented in the article
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Yongjie Hao, Wenyao Liu, Shuo Lu, and Yu Zhang "Applications of small optical correlator in traffic", Proc. SPIE 4921, Optical Manufacturing Technologies, (5 September 2002);

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