Rotation-invariant digital pattern recognition using circular harmonic expansion.

A new method has been developed for rotation-invariant pattern recognition. One component of the circular harmonic expansion of the target is used in the preparation of the reference. Correlations between the input and reference objects are accomplished by FFT and multiplication in the frequency domain. In an experience with targets from an image with 192 x 192 pixels, target orientations were detected with an accuracy of approximately 0.1 degrees . This method is also suitable for optical implementation.