Position, rotation, and intensity invariant recognizing method
First Claim
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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Abstract
A method for recognizing the presence of a particular target in a field of view which is target position, rotation, and intensity invariant includes the preparing of a target-specific invariant filter from a combination of all eigen-modes of a pattern of the particular target. Coherent radiation from the field of view is then imaged into an optical correlator in which the invariant filter is located. The invariant filter is rotated in the frequency plane of the 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. Any constant response is thus detected in the output
The U.S. Government has rights in this invention pursuant to Contract No. DE-AC04-76DP00789 between the U.S. Department of Energy and AT&T Technologies, Inc.
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Citations
6 Claims
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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:
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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 of imaging 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, and determining 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, and N=number of summations. - View Dependent Claims (2, 3, 4, 5, 6)
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Specification