Automatic Recognition And Tracking Of Targets From Visible Or Thermal Imagery, Using Optical Processing

(0272) 693831 Ext. 171/177AbstractA real -time Vander Lugt correlator for automatic recognition and tracking of targetsfrom visible or thermal data is described. A modification to the classical systemarchitecture was the use of difference -of- Gaussian spatial filtering, which providedgreater tolerance to scale and aspect variations in targets.Incoherent -to- coherent conversion was achieved using a Hughes LCLV, and the results ofa rigorous evaluation study of the device are discussed.IntroductionRecent research and development in the area of real -time spatial light modulators hasled to an upsurge of interest in optical information processing, in areas such as opticallogic, signal processing, and optical pattern recognition_A system is described which utilises a Hughes Liquid crystal light valve (LCLV) toimpose imagery, in near real time, onto the coherent beam of an optical correlator, withthe aim of achieving automatic recognition and tracking of targets. This is based uponthe classic Van der Lugt architecture (reference 1), but incorporates an intermediatespatial filtering stage, which provides a convenient means of modifying the Fourier spectraof both reference and input functions, in order to achieve increased tolerance to scale andorientation variations in targets.System operationA schematic diagram of the optical system is shown in Figure 1. There are two stagesinvolved in its use. The first is production of the matched spatial filter (MSF), and thesecond is correlation with input data. For production of the MSF, a reference function,either in the form of a suitably apertured target from within the field -of -view of theinput sensor, or a computer -generated, weighted combination function of a number of viewsof the target (reference 2), is introduced at plane P1, via a fibre -optic faceplate C.R.T.The Fourier transform of the reference function is formed at P2, where it is modifiedby the difference -of- Gaussian (DOG) filter, and the relay lens L then refocuses themodified Fourier transform at P