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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.
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