  In this paper, we show that our proposed hybrid optoelectronic correlator
(HOC), which correlates images using spatial light modulators (SLM), 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). We also illustrate a key
limitation of the ideas presented in previous papers on performing PMT and
present a solution to circumvent this limitation by cutting out a small circle
at the center of the Fourier Transform which precedes PMT. 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.
