ROTATIONALLY INVARIANT CORRELATOR

A rotationally invariant correlator which correlates an arbitrarily rotated image with a large database of similar stored images. The correlator initially scans the image to produce a two-dimensional array of pixels representative thereof. A plurality of concentric rings of pixel data are then produced from the two-dimensional array of pixels. A Fast Fourier Transform is taken of each ring of pixel data which produces an amplitude spectra of the frequency components of that ring of pixel data, which is then normalized. The normalized amplitude spectra for the image being correlated is then compared with normalized amplitude spectra of similar rings of pixel data for similar images in memory, and any matches are identified. The width of each ring of pixel data is selected to be smaller than the size of the smallest features which are to be resolved, while being sufficiently wide to smooth out extraneous noise. Several of the processing steps for each ring of pixel data are performed in parallel in parallel processing arrangements.