Binary phase only reference for invariant pattern recognition with the joint transform correlator

Abstract

The joint transform correlator (JTC) is one of two main optical image processing architectures which provide us with a highly effective way of comparing images in a wide range of applications. Traditionally an optical correlator is used to compare an unknown input scene with a pre-captured reference image library, to detect if the reference occurs within the input. There is a new class of application for the JTC where they are used as image comparators, not having a known reference image, rather frames from a video sequence form both the input and reference. The JTC input plane is formed by combining the current frame with the previous frame in a video sequence and if the frames match, then there will be a correlation peak. If the objects move then the peaks will move (tracking) and if something has changed in the scene, then the correlation between the two frames is lost. This forms the basis of a very powerful application for the JTC in Defense and Security. Any change in the scene can be recorded and with the inherent shift invariance property of the correlator, any movement of the objects in the scene can also be detected. A major limitation of the JTC is its intolerance to rotation and scale changes in input compared to the reference images. The strength of the correlation signal decreases as the input object rotates or varies in scale relative to the reference object. We have designed binary phase only filters using the direct binary search algorithm for rotation invariant pattern recognition for a 1/f JTC. Simulation and experimental results are included. If the relative alignment of the images in the input plane is known then the desirable fringes in the resulting joint power spectrum (JPS) can be selectively enhanced during the binarisation process. This can have a highly beneficial effect on the resulting correlation intensities. For the input plane in which input and reference images are placed side by side we develop the vertical edge enhancement (VEE) technique that concentrate solely on the vertical components of the JPS during the binarisation process. Simulation and experiments proves that VEE enhances the correlation intensities and suppresses the zero order noise.© (2006) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.