Position, rotation, and intensity invariant recognizing method

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 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 I k =intensity value at each pixel k, and N=number of summations.

Claim 2

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 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 I k =intensity value at each pixel k, and N=number of summations.