Showing papers by "Eero P. Simoncelli published in 1996"

Noise removal via Bayesian wavelet coring

Abstract: The classical solution to the noise removal problem is the Wiener filter, which utilizes the second-order statistics of the Fourier decomposition. Subband decompositions of natural images have significantly non-Gaussian higher-order point statistics; these statistics capture image properties that elude Fourier-based techniques. We develop a Bayesian estimator that is a natural extension of the Wiener solution, and that exploits these higher-order statistics. The resulting nonlinear estimator performs a "coring" operation. We provide a simple model for the subband statistics, and use it to develop a semi-blind noise removal algorithm based on a steerable wavelet pyramid.

Computational models of cortical visual processing

Abstract: The visual responses of neurons in the cerebral cortex were first adequately characterized in the 1960s by D. H. Hubel and T. N. Wiesel [(1962) J. Physiol. (London) 160, 106-154; (1968) J. Physiol. (London) 195, 215-243] using qualitative analyses based on simple geometric visual targets. Over the past 30 years, it has become common to consider the properties of these neurons by attempting to make formal descriptions of these transformations they execute on the visual image. Most such models have their roots in linear-systems approaches pioneered in the retina by C. Enroth-Cugell and J. R. Robson [(1966) J. Physiol. (London) 187, 517-552], but it is clear that purely linear models of cortical neurons are inadequate. We present two related models: one designed to account for the responses of simple cells in primary visual cortex (V1) and one designed to account for the responses of pattern direction selective cells in MT (or V5), an extrastriate visual area thought to be involved in the analysis of visual motion. These models share a common structure that operates in the same way on different kinds of input, and instantiate the widely held view that computational strategies are similar throughout the cerebral cortex. Implementations of these models for Macintosh microcomputers are available and can be used to explore the models' properties.

Steerable wedge filters for local orientation analysis

Abstract: Steerable filters have been used to analyze local orientation patterns in imagery. Such filters are typically based on directional derivatives, whose symmetry produces orientation responses that are periodic with period /spl pi/, independent of image structure. We present a more general set of steerable filters that alleviate this problem.

A filter design technique for steerable pyramid image transforms

Abstract: We describe a novel recursive filter design technique for multi-scale "pyramid" transforms. The recursion in the design technique follows that of the pyramid construction, and allows us to solve a reduced design problem at each step. We demonstrate the use of this technique by designing filters of various orientation bandwidths for use in a "steerable pyramid" image transform.

A rotation invariant pattern signature

Abstract: We propose a "signature" for rotation-invariant representation of local image structure. The signature is a complex-valued vector constructed analytically from the projections of the image onto a set of oriented basis kernels. The components of the signature form an over-complete set of algebraic invariants, but are chosen to avoid instabilities associated with previously developed algebraic invariants. We demonstrate the use of this signature for representing and classifying junctions in grayscale imagery.

Single lens range imaging method and apparatus

Abstract: A single lens range sensor comprises a camera (27) having a pair of plano-convex lenses (28a, 28b), an optical mask (30), an imaging sensor (32), a digitizer (34) and a computer (36). The optical mask (30) may be implemented with a liquid crystal array having spatially varying opacity which can be switched (e.g., by the computer) (36) between masks derived from a differentiable mask function and its derivative. Alternatively, the mask (30) may be composed of two printed masks which are mechanically switched to obtain two images based on the differentiable mask function and its derivative. The imaging sensor (32) may be implemented with a CCD array. The invention avoids the correspondence problems of the two camera and moving camera approaches, and is simple to calibrate.

Direct Differential Range Estimation Using Optical Masks

Abstract: We describe a novel formulation of the range recovery problem, based on computation of the differential variation in image intensities with respect to changes in camera position. The method uses a single stationary camera and a pair of calibrated optical masks to directly measure this differential quantity. The subsequent computation of the range image is simple and should be suitable for real-time implementation. We also describe a variant of this technique, based on direct measurement of the differential change in image intensities with respect to aperture size. These methods are comparable in accuracy to other single-lens ranging techniques. We demonstrate the potential of our approach with a simple example.

Appareil capteur d'images monoculaire et procede associe

Abstract: Un capteur d'images monoculaire comporte une camera (27) presentant une paire de lentilles plano-convexes (28a, 28b), un masque optique (30), un capteur d'images (32), un numeriseur (34) et un ordinateur (36). Le masque optique (30) peut etre equipe d'une matrice a cristaux liquides presentant une opacite variable dans l'espace, qui peut etre basculee (par exemple par l'ordinateur 36) entre des masques derives d'une fonction differentiable et sa derivee. Le masque (30) peut egalement se composer de deux masques imprimes qui sont bascules mecaniquement de sorte que deux images soient produites selon la fonction differentiable et sa derivee. Le capteur d'images (32) peut etre equipe d'une matrice a CCD. Avec l'appareil et le procede selon l'invention, on evite le probleme de correspondance inherent aux techniques a deux cameras et a une camera en mouvement, et l'etalonnage en est simplifie.