Extraction of a Property of Visual Patterns by Fraunhofer Diffraction

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Abstract
A simple method is proposed to extract an information concerning relative orientation of straight lines which are contained in a visual pattern such as a character or a numeral by making use of Fraunhofer diffraction produced by a laser beam. When a pattern has straight lines, the diffraction pattern also has straight lines, all of which pass through a point (zero-order point) in the diffraction plane and each of which is perpendicular to the corresponding original one. The use of a rotating straight slit in the diffraction plane and a photomultiplier unit behind it enables us to obtain an electric time-signal which shows maxima corresponding to straight lines in the original pattern. The mutual separation of the maxima informs us of their relative orientation. The extraction of information is carried out quite independently of the position and the orientation of the original pattern.

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