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Applied Optics

Applied Optics

APPLICATIONS-CENTERED RESEARCH IN OPTICS

  • Editor: James C. Wyant
  • Vol. 46, Iss. 33 — Nov. 20, 2007
  • pp: 7970–7977

Log-polar transform-based wavelet-modified maximum average correlation height filter for distortion invariance in a hybrid digital–optical correlator

Amit Aran, Naveen K. Nishchal, Vinod K. Beri, and Arun K. Gupta  »View Author Affiliations


Applied Optics, Vol. 46, Issue 33, pp. 7970-7977 (2007)
http://dx.doi.org/10.1364/AO.46.007970


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Abstract

We discuss and implement a log-polar transform-based distortion-invariant filter for automatic target recognition applications. The log-polar transform is a known space-invariant image representation used in several image vision systems to eliminate the effects of scale and rotation in an image. For in-plane rotation invariance and scale invariance, a log-polar transform-based filter was synthesized. In cases of in-plane rotation invariance, peaks shift horizontally, and in cases of scale invariance, peaks shift vertically. To achieve out-of-plane rotation invariance, log-polar images were used to train the wavelet-modified maximum average correlation height (WaveMACH) filter. The designed filters were implemented in the hybrid digital–optical correlation scheme. It was observed that, for a certain range of rotation and scale differences, the correlation signals merge with the strong dc. To solve this problem a shift was introduced in the log-polar image of the target. The use of a chirp function for dc removal has also been discussed. Correlation peak height and peak-to-sidelobe ratio have been calculated as metrics of goodness of the log-polar transform-based WaveMACH filter. Experimental results are presented.

© 2007 Optical Society of America

OCIS Codes
(070.0070) Fourier optics and signal processing : Fourier optics and signal processing
(070.4550) Fourier optics and signal processing : Correlators
(070.5010) Fourier optics and signal processing : Pattern recognition
(100.3008) Image processing : Image recognition, algorithms and filters

ToC Category:
Fourier Optics and Signal Processing

History
Original Manuscript: June 25, 2007
Revised Manuscript: October 2, 2007
Manuscript Accepted: October 3, 2007
Published: November 12, 2007

Citation
Amit Aran, Naveen K. Nishchal, Vinod K. Beri, and Arun K. Gupta, "Log-polar transform-based wavelet-modified maximum average correlation height filter for distortion invariance in a hybrid digital-optical correlator," Appl. Opt. 46, 7970-7977 (2007)
http://www.opticsinfobase.org/ao/abstract.cfm?URI=ao-46-33-7970

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