1. Field of the Invention:
The present invention relates to optical signal processing using electron trapping materials, and more specifically, to the use of electron trapping materials for incoherent image subtraction.
2. Description of the Related Art:
The capabilities of electron trapping materials having been demonstrated in various disciplines of optical signal processing. For example, the application of electron trapping materials to parallel Boolean logic has been reported by S. Jutamulia, G. M. Storti, J. Lindmayer, and W. Seiderman in "Application of Electron Trapping (ET) Materials to Optical Parallel Logic Processing," Proc. SPIE, 1151, 83, 1989. The use of electron trapping materials in memory devices has been demonstrated by S. Jutamulia, J. Lindmayer, and G. Storti in "Optical Pattern Recognition and Associative Memory Using Electron Trapping Materials," Proc. SPIE 1053, 67, 1989. Recently, the capabilities of electron trapping materials applied to Hopfield type neural networks has been discussed by S. Jutamulia, G. M. Storti, J. Lindmayer, W. Seiderman in "Optical Neural Network Digital Multi-Value Processor with Learning Capability Using Electron Trapping Materials," Proc. SPIE 1215, 457, 1990.
Other areas of optical signal processing have the potential to realize further advances from the continuing developments in electron trapping material applications. One such area of particular current interest is that of image subtraction, which has proved very useful in automatic surveillance and inspection. Image subtraction techniques can also be applied to bandwidth compression in communication based on an interframe coding paradigm, such as described by T. J. Lynch in Data Compression, Techniques and Applications, Lifetime Learning, Belmont, Calif., 1985.
There are several known methods for optically subtracting one image from another in order to detect differences between scenes. A review of various image subtraction techniques has been presented in a classic paper by J. F. Ebersole, "Optical Image Subtraction," Opt. Eng. 14, 426, 1975, as well as in a more recent paper by H. K. Liu and T. H. Chao, "Optical Image Subtraction Techniques, 1975-1985," Proc. SPIE 638, 55, 1986. Rapid progress in the development of real-time electro-optic devices has also stimulated many new techniques in image subtraction, such as those reported by F. T. S. Yu, M. F. Cao, and X. J. Lu, in "Real-Time Programmable Image Subtractor Using a Magnetooptic Device," Appl. Opt. 25, 3773, 1986; see also F. T. S. Yu, S. Jutamulia, D. A. Gregory, "Real-Time Liquid Crystal TV XOR- and XNOR- Gate Binary Image Subtraction Technique," Appl. Opt. 26, 2738, 1987.
These known techniques as reported in the cited publications, however, have limitations, such as a low space-bandwidth product (SBP), coherent noise, and difficulty in performing gray level image subtraction.
While progress has been made in the area of optical imagery, the features and advantage of electron trapping materials to image subtraction has heretofore been lacking. While current techniques are satisfactory in some applications, they do not overcome the limitations mentioned above that presently exist in the field, nor do they provide the advantages realized with the use of electron trapping materials to image subtraction using the method described below.