Incorporation of polar Mellin transform in a hybrid optoelectronic correlator for scale and rotation invariant target recognition.

In this paper, we show that our proposed hybrid optoelectronic correlator (HOC), which correlates images using spatial light modulators (SLMs), detectors, and field-programmable gate arrays (FPGAs), is capable of detecting objects in a scale and rotation invariant manner, along with the shift invariance feature, by incorporating polar Mellin transform (PMT). For realistic images, we cut out a small circle at the center of the Fourier transform domain, as required for PMT, and illustrate how this process corresponds to correlating images with real and imaginary parts. Furthermore, we show how to carry out shift, rotation, and scale invariant detection of multiple matching objects simultaneously, a process previously thought to be incompatible with PMT-based correlators. We present results of numerical simulations to validate the concepts.