Rotation-invariant binary joint transform correlator

A novel thresholding method is proposed in a binary joint transform correlator (BJTC). We select the power spectrum of the reference pattern, instead of the joint transform power spectra of the reference and the target patterns, as the thresholding value. Compared with the routine BJTC, the additional real-time recording of the power spectrum of the target is avoided, and the procedure of the pattern recognition is reduced. Then the BJTC is combined with the circular harmonic expansion technique to achieve rotation invariance. Computer simulation results show that the circular-harmonic-based BJTC possesses high light efficiency, high discrimination capability, as well as good rotation invariance.