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Position, rotation, and intensity invariant recognizing method

  • US 4,838,644 A
  • Filed: 09/15/1987
  • Issued: 06/13/1989
  • Est. Priority Date: 09/15/1987
  • Status: Expired due to Fees
First Claim
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1. A method of recognizing the presence of a particular target in a field of view which is target position, rotation, and intensity invariant, comprising the steps of:

  • preparing a target-specific filter, which is invariant to geometric distortions in target pattern due to changes in position in the field of view, rotation and intensity, from a combination of all eigen-modes of a pattern of the particular target;

    imaging coherent radiation from the field of view into an optical correlator;

    rotating said filter in the frequency plane of an optical correlator in order to produce a constant-amplitude rotational response in a correlation output plane when the particular target is present in the field of view; and

    detecting any constant amplitude response in the output plane to determine whether a particular target is present in the field of view, wherein said detecting step includes the steps ofimaging a temporal pattern in the output plane with an optical detector having a plurality of pixels, said imaging occuring at a plurality of different arbitrary angles of rotation of the filter with angular separation sufficient to decorrelate successive frames, anddetermining a correlation coefficient for each pixel where a correlation coefficient of unity indicates the presence of a temporal signature of the particular target, wherein said step of determining a correlation coefficient includes the steps of accumulating the intensity and intensity-squared of each pixel such that the correlation coefficient is calculated from ##EQU7## where Ik =intensity value at each pixel k, andN=number of summations.

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