Litton Systems, Inc.

Phillip Wayne Dennis

Stuart A Mills

Robert Barry Dydyk

The invention corrects for rotational misalignment of images having a prominent periodic structure in a preferred direction, particularly imaged text pages. It preferably also finds the degree of correlation between different images. First the rotational misalignment of an imaged page is detected and corrected, bringing the page into alignment with an axis. The angle of rotation of the page is detected by performing a linear regression analysis on filtered, two-dimensional power spectral density distribution of the page, to find the angular orientation of the periodic components. In the preferred embodiment, two imaged pages are then cross-correlated, preferably by an optical correlator, to find the degree of correlation between the pages.

Rotational correction and duplicate image identification by fourier transform correlation

The present invention is a method and apparatus for automatically placing a first unknown image, such as an unknown fingerprint image, into one of a plurality of categories. The invention includes storing in a library a plurality of value series, each of which series is derived from the frequency representation of an image category. The categorization process and apparatus takes the frequency image of a first unknown pattern to create a first frequency image. The frequency image plane of the first (unknown) frequency image is divided into a plurality of frequency image plane regions. Each of the frequency image plane regions may be an angular segment radiating from the origin of the frequency image plane. A region value is assigned to each of the frequency image plane regions based on the total energy in the frequency image in that region. The region values for the first frequency image are combined to generate a first series of region values. The first series of region values is compared in a comparator with each of the stored value series. The comparator preferably performs a correlation function on the pattern or series of the regional values using the one dimensional frequency transform of the spatial representation of the pattern of series of regional values.

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Thousand Oaks, CA, United States of America

Phillip Wayne Dennis