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Title: Invariant binary phase only filters for Joint Transform Correlator
Author: Butt, J. A.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2005
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Many JTC systems are constructed with the use of ferroelectric liquid crystal (FLC) spatial light modulators (SLMs) as they provide fast two dimensional binary modulation of coherent light. Due to the binary nature of the FLC SLMs used in the JTC systems, any image addressed to the device need to have some form of thresholding. Carefully thresholding the grey scale input plane and the joint power spectrum (JPS) has significant effect on the quality of correlation peaks and zero order (DC) noise. A new thresholding technique to binarise the JPS has been developed and implemented optically. This algorithm selectivity enhances the desirable fringes in the JPS which provide correlation peaks of higher intensity. Zero order noise is further reduced when compared to existing thresholding techniques. Keeping in mind the architecture of the JTC and limitations of FLC SLMs, a new technique to design rotation and scale invariant binary phase only filters for the JTC architecture is presented. Filers design with this technique have limited dynamic range, higher discriminability among target and non-target objects, and convenience for implementation on FLC SLMs. Simulation and experiments shows excellent results of various rotation and scale invariant filters designed with this technique. A rotation invariant filter is needed for various machine vision applications of the JTC. By fixing the distance between the camera and the input object, the scale sensitivity of the correlator can be avoided. In contrast to the industrial machine vision applications scale factor is very important factor for the applications of the JTC systems in defence and security. A security system using a scale invariant JTC will be able to detect a target object well in advance and will provide more time to take a decision. The CCD camera used in the current JTC system has limited dynamic range. Since intensities are distributed over a huge range in the JPS, a large amount of information is lost at the point of capture, particularly in areas where CCD array is saturated. Due to the camera saturation it is difficult to make a direct comparison with the experimental results. Hence, replacing the current CCD camera with equivalent CMOS camera would minimise the amount of information lost and avoid the camera saturation.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available