Optical absolute difference measurement for gray-scale image matching

In this paper absolute difference measurement (ADM) is proposed for optical gray-scale image recognition. ADM measures the similarity between different gray-scale images and the value of measurement reflects the similarity linearly. Using optical correlation and a novel cycle-encoding method the processing of gray-scale image matching based on absolute difference measurement can be realized simply. This new method can be used in coherent correlators or incoherent correlators. In this paper a compact hybrid image recognition unit (CHIRU) based on an incoherent correlator is constructed. The system has good fault-tolerance ability for rotation distortion, Gauss noise disturbance or information losing. In the experiments some pictures of military objects are processed. The recognition speed is 12 frames per second and the accuracy of recognition is more than 95 percent.