Henri H. Arsenault

Experiments on pattern recognition using invariant Fourier-Mellin descriptors.

Image descriptors based on the circular-Fourier-radial-Mellin transform are used for position-, rotation-, scale-, and intensity-invariant multiclass pattern recognition. The orders of the radial moments and of the circular harmonics are chosen to obtain an efficient image description. The first-order radial moments of three circular harmonics are sufficient to obtain a satisfactory recognition performance. The influence of additive noise is investigated. Experimental results are shown.

Optical pattern recognition using circular harmonic expansion

Presented in this paper is an optical implementation of a shift- and rotation-invariant pattern recognition technique. A computer-generated hologram is designed to match with one of the circular harmonic components of the target. Experimental results with simple photographic objects show that targets with different locations and orientations can be simultaneously recognized by the optical system.

Rotation-invariant digital pattern recognition using circular harmonic expansion

A new method has been developed for rotation-invariant pattern recognition. One component of the circular harmonic expansion of the target is used in the preparation of the reference. Correlations between the input and reference objects are accomplished by FFT and multiplication in the frequency domain. In an experience with targets from an image with 192 x 192 pixels, target orientations were detected with an accuracy of approximately 0.1 degrees . This method is also suitable for optical implementation.

Properties of speckle integrated with a finite aperture and logarithmically transformed

When image plane speckle intensity integrated over a finite aperture is submitted to a logarithmic transformation, the noise becomes additive and signal independent. The first- and second-order moments of the probability distribution are derived. It is found that the logarithm of speckle noise approaches a normal distribution much faster than speckle intensity. The properties of speckle noise are different from those of film-grain noise; for example, neither Nutting’s law nor Selwyn’s law is satisfied by speckle.

Image Formation for Coherent Diffuse Objects: Statistical Properties

The properties of the amplitude and illuminance of the images of coherently illuminated diffuse objects are studied. Uniform and nonuniform objects are considered. The image illuminance is considered to result from a linear transformation of a nonstationary gaussian stochastic process followed by a square-law detection. Expressions are obtained for the mean, autocorrelation, variance, and spatial power spectral density of the amplitude and of the illuminance. Interpretation of the results led to conclusions concerning the speckle size, the noise power in the image, and the transfer function of an optical system when the object diffuses coherent light. When the autocorrelation width of the random fluctuations of the object amplitude is small compared to the impulse response of the system, the mean illuminance in the image plane is that which would be given by an incoherent object having the same luminance as the object considered; the average speckle size is equal to that of the impulse response of the system; the average transfer function of the system is the incoherent transfer function; and the distribution of the noise spatial frequencies does not depend upon the form of the signal, but only upon its total energy. Other results concerning the image statistics have also been obtained.

Pattern discrimination by multiple circular harmonic components

Multiple circular harmonic components of the same target can be used jointly to discriminate between the target and other objects. Two methods are considered: Coherent superposition and decision making in multidimensional space. Experimental results for the discrimination between a tank and a truck are given.

Phase calibration and applications of a liquid-crystal spatial light modulator

A simple phase-characterization method for spatial light modulators is proposed. The low-cost method permits high-precision measurement and provides data for the setting of the spatial-light-modulator operating point in the phase-modulation mode. The dynamic phase response is used to perform efficient kinoform recording. In order to record the kinoform, we modify the global iterative coding to compute phase holograms. Finally, modified phase-phase correlation is introduced. The phase-phase correlator permits sharper correlation peaks, better energy transmission, and higher discrimination than an amplitude-phase correlation. Optical experimental results are presented.

Combined homomorphic and local-statistics processing for restoration of images degraded by signal-dependent noise

The generalized homomorphic transformation to make signal-dependent noise independent of the signal is combined with a local-statistics image restoration technique to process images degraded by signal-dependent noise. Experimental results are given for images degraded by film-grain noise and by multiplicative noise.

Properties of the circular harmonic expansion for rotation-invariant pattern recognition

Some general properties of the circular harmonic expansion relevant to their use for pattern recognition are derived. Both circular harmonic filters and Fourier-Mellin descriptors, which are used as the moments of circular harmonic functions, are considered. Expressions for the asymptotic energy in terms of the circular harmonic orders are derived and experimentally verified.

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.