Luc Leclerc

Rotation invariant phase-only and binary phase-only correlation.

Phase-only circular harmonic filters and binary phase-only circular harmonic filters are proposed. Both filters have full rotation invariance and excellent performance for discrimination between objects and against background noise. Their properties have been studied and implemented for computer applications. The binary filters are appropriate for real-time applications using spatial light modulators.

Optical binary phase-only filters for circular harmonic correlations

In our previous paper we proposed using successively binary cosine and sine filters and combining the correlation intensities for rotation-invariant phase-only circular harmonic correlation. This paper presents an alternative method that uses a single filter. We present theory and optical and computer experimental results to show that, with a spatial frequency carrier, the binary phase-only filter [1, -1] and the binary filter [1, 0] yield the impulse response of a continuous phase-only filter. Compared with conventional computer-generated holographic filters, the binary phase-only filter and the binary filter have no representation-related error, require a minimum space-bandwidth product, and may be implemented in a spatial light modulator.

Circular harmonic covariance filters for rotation invariant object recognition and discrimination

Abstract We propose using the covariance function as a measure of similarity in the circular harmonic matched filters for rotation invariant pattern recognition and for discrimination against unwanted objects which are unknown a priori. An optical covariance filter is introduced, which is a modified circular harmonic composite filter combining a conventional circular harmonic filter with a uniform circular harmonic function. Both optical and computer experiments show improved discrimination capability.

Similarity And Invariance In Pattern Recognition

The arbitrary nature of the concept of similarity is discussed, and its consequences on the exploitation of invariants in pattern recognition. After briefly reviewing the main invariants of interest in automated pattern recognition, methods of achieving invariant pattern recognition are reviewed, with emphasis on the use of matched spatial filters made with Circular harmonic components. The progress in using such filters and their derivatives with sidelobe-rejection capability on images of increasing complexity, from simple binary shapes to complex grey-level objects on highly cluttered backgrounds, is described.

New emission band from a superradiant travelling-wave rhodamine 6G dye laser☆

Abstract A new emission band from a superradiant travelling-wave rhodamine 6G dye laser was observed only at high dye concentrations. It was verified to be due to emission from rhodamine 6G dimers.

Methods for reducing sidelobes associated with composite filters

Abstract We propose two new methods for reducing sidelobes associated with pattern recognition using composite filters, which are linear combinations of matched filters. The recognition of objects on uniform and on cluttered backgrounds are both discussed. Experiments on aircraft comparing these methods with previously published methods indicate that the new methods yield the best results.

Real-time binary phase-only circular harmonic filters using a liquid crystal television in the Fourier plane of an optical correlator

A rotation invariant optical correlator using a low-cost, liquid crystal television (LCTV) in the Fourier plane is described. The performance of the LCTV used as a filter support medium is evaluated, using interferometric measurements and an image reconstruction experiment. Different operating modes of an LCTV suitable for encoding binary phase-only filters are discussed. Finally, a modified LCTV is used in the filter plane of a conventional 4-f correlator to encode unipolar binary phase-only matched filters and unipolar binary phase-only circular harmonic filters. Optical experimental results are compared with the results of computer experiments.

New ways of using optics for faster pattern recognition

We review recent work on rotation invariant pattern recognition. We briefly review results involving Circular harmonic filters, then describe some of our more recent research in this area. A pattern classification system that achieves rotation invariance by means of an optical rectangular-to-polar coordinate transformation is described, as well as a system using circular sampling. Experimental results using optical systems are presented for all those methods.

Multiplexed binary phase-only circular harmonic filters

Multiplexed binary phase-only filters provide simultaneously multiple correlations for an input object. A theoretical harmonic analysis allows estimation of the crosstalk among component filters, caused by the nonlinear binarization. A method thresholding a combination of the component phase-only filters is proposed to recover the correlation peak intensities of the component filters. Experimental results using multiplexed binary phase-only circular harmonic filters for rotation invariant pattern recognition is presented.

Theoretical approach to the sidelobes in composite filters

Abstract We present some theoretical considerations on the appearance of sidelobes in the pattern recognition process when use is made of the composite filter of Caulfield and Maloney. The results previously obtained in this field by us and other workers are discussed.