Discrimination-sensitive rotation-invariant joint-transform correlator using gradient preprocessing and circular harmonic components

The advantage of discrimination sensitivity of a preprocessed binarized joint-transform correlator (PBJTC) has been combined with the rotational tolerance of circular harmonic component (CHC) analysis to realize a JTC which gives a discrimination-sensitive, rotation-invariant pattern recognition system. Both computer simulation and experimental results are provided. The use of gradient preprocessing and adaptive binarization helps in suppressing the sidelobes otherwise associated with a conventional CHC-based JTC. The simulation study shows that such a composite JTC gives a sharp correlation peak for the rotated target and discriminates nontarget, producing a very low crosscorrelation peak that stays below the detection threshold. Although it involves two additional improvisation steps (gradient preprocessing and computation of the CHCs), they can be performed prior to the correlation operation, and the simple binarization process can be realized faster optically along with a dedicated digital comparator. (C) 1998 Society of Photo-Optical Instrumentation Engineers. [S0091-3286(98)01301-4].