David Casasent

Minimum average correlation energy filters

The synthesis of a new category of spatial filters that produces sharp output correlation peaks with controlled peak values is considered. The sharp nature of the correlation peak is the major feature emphasized, since it facilitates target detection. Since these filters minimize the average correlation plane energy as the first step in filter synthesis, we refer to them as minimum average correlation energy filters. Experimental laboratory results from optical implementation of the filters are also presented and discussed.

Position, rotation, and scale invariant optical correlation

A new optical transformation that combines geometrical coordinate transformations with the conventional optical Fourier transform is described. The resultant transformations are invariant to both scale and rotational changes in the input object or function. Extensions of these operations to optical pattern recognition and initial experimental demonstrations are also presented.

Spatial light modulators

Near real-time reusable spatial light modulators for coherent optical data processing are reviewed. The PROM, liquid crystal, and electron beam addressed DKDP and oil film light valves appear to be the most promising devices for coherent optical data processing.

Multivariant technique for multiclass pattern recognition

A technique for multiclass optical pattern recognition of different perspective views of an object is described. Each multiclass representation of an object is described as an orthonormal basis function expansion, and a single averaged matched spatial filter is then produced from a weighted linear combination of these functions. The technique is demonstrated for a terminal missile guidance application using IR tank imagery.

Unified synthetic discriminant function computational formulation.

A most attractive approach to distortion-invariant pattern recognition uses a synthetic discriminant function (SDF) as the matched spatial filter in a correlator. In this paper, we (1) provide a general basis function and hyperspace description of SDFs, (2) advance a derivation showing the generality of the correlation matrix observation space that we use in our filter synthesis, and (3) detail a unified SDF filter synthesis technique for five different types of pattern recognition problem.

New optical transforms for pattern recognition

New optical transformations are discussed. These include Mellin transforms, Fourier-Mellin transforms, and combinations of Geometrical transformations and Fourier-Mellin operations. Scale, postional, and rotational invariant correlations with no loss in SNR are demonstrated.

Application Of The Liquid Crystal Light Valve To Real-Time Optical Data Processing

This paper reviews the hybrid field-effect liquid crystal light valve (LCLV) and its application to real-time coherent optical data processing. The light valve is basically a high resolution optical-to-optical image converter. The device embodies a CdS photoconductor, a CdTe light-absorbing layer, a dielectric mirror, and a biphenyl liquid crystal layer sandwiched between indium-tin-oxide transparent electrodes deposited on optical quality glass flats. The input image is directed onto the photo-conductor to reduce the impedance of the photoconductor, thereby switching the ac voltage that is impressed across the electrodes onto the liquid crystal to activate the device. The ac operation ensures long operating life for the device. The liquid crystal is operated in a hybrid field-effect mode. It utilizes the twisted nematic effect to create a dark off-state (voltage off the liquid crystal) and optical birefringence to create the bright on-state. The liquid crystal modulates the phase of the coherent readout light. By an additional analyzer an intensity modulation is created.

Correlation Synthetic Discriminant Functions

Advanced filters are described for distortion-invariant space-invariant object identification and location in clutter using correlators. These correlation synthetic discriminant functions (SDFs) are extensions of earlier projection SDFs. They provide control of the sidelobe levels and the shape of the output correlation function as well as its peak intensity. The theory for synthesis of three such SDFs and a discussion of correlation plane detection criteria for use with these filters are presented.

SCALE INVARIANT OPTICAL CORRELATION USING MELLIN TRANSFORMS

The use of optical Mellin transforms in matched spatial filter correlation of imagery that differs in scale is discussed. Theoretical considerations and initial experimental results are included. The intensity of the correlation peak is found to be indeigendent of the input scale, and the scale difference between the two functions to be correlated can also be extracted from the location of the correlation peak.

Detection filters and algorithm fusion for ATR

Detection involves locating all candidate regions of interest (objects) in a scene independent of the object class with object distortions and contrast differences, etc., present. It is one of the most formidable problems in automatic target recognition, since it involves analysis of every local scene region. We consider new detection algorithms and the fusion of their outputs to reduce the probability of false alarm P(FA) while maintaining high probability of detection P(D). Emphasis is given to detecting obscured targets in infrared imagery.