Biomedical subjects

A Yuille

Publications and source records attributed to A Yuille.

3 recordsLinked to original sources

PubMed1989

Stereo and eye movement.

We describe a method to solve stereo correspondence using controlled eye (or camera) movements. Eye movements supply additional image frames and monocular depth estimate, which can be used to constrain stereo matching. Because the eye movements are small, traditional stereo techniques of stereo with multiple frame will not work. We develop an alternative approach using a systematic analysis to define a probability distribution for the errors. Our matching strategy then matches the most probable points first, thereby reducing the ambiguity for the remaining matches. We demonstrate this algorithms with several examples.

Computer Simulation↗

PubMed1987

A method for computing spectral reflectance.

Psychophysical experiments show that the perceived colour of an object is relatively independent of the spectrum of the incident illumination and mainly depends on the surface spectral reflectance. We first demonstrate a possible solution to this undetermined problem for a Mondrian world of flat rectangular patches. We expand the illumination and surface reflectances in terms of a finite number of basis functions. We assume that the number of colour receptors is greater than the number of basis functions. This yields a set of nonlinear equations for each colour patch. Number counting arguments show that, given a sufficient number of surface patches with the same illumination, there are enough equations to determine the surface reflectances up to an overall scaling factor. This theory is similar to previous and independent work by Maloney and Wandell (Maloney 1985). We demonstrate a simple method of solving these non-linear equations. We generalize to situations where the illumination varies in space and the objects are three dimensional shapes. To do this we define a method for detecting material changes, a colour edge detector, and illustrate a way of detecting the colour of a material at its boundaries and propagating it inwards.

Color Perception↗

PubMed1986

Analog "neuronal" networks in early vision.

Many problems in early vision can be formulated in terms of minimizing a cost function. Examples are shape from shading, edge detection, motion analysis, structure from motion, and surface interpolation. As shown by Poggio and Koch [Poggio, T. & Koch, C. (1985) Proc. R. Soc. London, Ser. B 226, 303-323], quadratic variational problems, an important subset of early vision tasks, can be "solved" by linear, analog electrical, or chemical networks. However, in the presence of discontinuities, the cost function is nonquadratic, raising the question of designing efficient algorithms for computing the optimal solution. Recently, Hopfield and Tank [Hopfield, J. J. & Tank, D. W. (1985) Biol. Cybern. 52, 141-152] have shown that networks of nonlinear analog "neurons" can be effective in computing the solution of optimization problems. We show how these networks can be generalized to solve the nonconvex energy functionals of early vision. We illustrate this approach by implementing a specific analog network, solving the problem of reconstructing a smooth surface from sparse data while preserving its discontinuities. These results suggest a novel computational strategy for solving early vision problems in both biological and real-time artificial vision systems.

Humans↗