Position, rotation, and intensity invariant recognizing method
A method is described 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 plant 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 plane to determine whether a particular target is present in the field of view. Preferably, a temporal pattern is imaged in the output plane with an optical detector having a plurality of pixels and a correlation coefficient for each pixel is determined by accumulating the intensity and intensity-squared of each pixel. The orbiting of the constant response caused by the filter rotation is also preferably eliminated either by the use of two orthogonal mirrors pivoted correspondingly to the rotation of the filter or the attaching of a refracting wedge to the filter to remove the offset angle. Preferably, detection of the temporal pattern in the output plane is performed at a plurality of arbitrary angles with angular separation sufficient to decorrelate successive frames.
- Assignee:
- Dept. of Energy, Washington, DC
- Patent Number(s):
- US 4838644
- OSTI ID:
- 5413188
- Resource Relation:
- Patent File Date: 15 Sep 1987
- Country of Publication:
- United States
- Language:
- English
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