A computational theory of human stereo vision.

An algorithm is proposed for solving the stereoscopic matching problem. The algorithm consists of five steps: (1) Each image is filtered at different orientations with bar masks of four sizes that increase with eccentricity; the equivalent filters are one or two octaves wide. (2) Zero-crossings in the filtered images, which roughly correspond to edges, are localized. Positions of the ends of lines and edges are also found. (3) For each mask orientation and size, matching takes place between pairs of zero-crossings or terminationss of the same sign in the two images, for a range of disparities up to about the width of the mask's central region. (4) Wide masks can control vergence movements, thus causing small masks to come into correspondence. (5) When a correspondence is achieved, it is stored in a dynamic buffer, called the 2 1/2-D sketch. It is shown that this proposal provides a theoretical framework for most existing psychophysical and neurophysiological data about stereopsis. Several critical experimental predictions are also made, for instance about the size of Panum's area under various conditions. The results of such experiments would tell us whether, for example, cooperativity is necessary for the matching process.     

Three-dimensional displays and stereo vision

Procedures for three-dimensional image reconstruction that are based on the optical and neural apparatus of human stereoscopic vision have to be designed to work in conjunction with it. The principal methods of implementing stereo displays are described. Properties of the human visual system are outlined as they relate to depth discrimination capabilities and achieving optimal performance in stereo tasks. The concept of depth rendition is introduced to define the change in the parameters of three-dimensional configurations for cases in which the physical disposition of the stereo camera with respect to the viewed object differs from that of the observer's eyes.     

A comparison of neural computations underlying stereo vision and sound localization.

Stereo vision and sound localization are behaviors that help organisms to orient in space. Stereo vision provides information about the distance of an object. In sound localization mainly directional signals are analyzed. Two specific cues, binocular disparities underlying stereo vision, and the interaural time difference, suited to represent azimuth in sound localization, have many computational problems in common, although they are generated in two different modalities. The extraction of both cues requires a comparison of signals that arise from two independent sensors, called two-sensor comparison here. This two-sensor comparison is achieved by algorithms similar to summation, half-wave rectification and multiplication. Since the underlying neurons are band-pass filters, the two-sensor comparison results in ambiguities. These are removed in a hierarchical way in several computational steps, involving squaring, inhibition and across-frequency integration.     

A shared vision

One of today's most powerful technologies in biomedical research--the creation of mutant mice by gene targeting in embryonic stem (ES) cells--was finally celebrated in this year's Nobel Prize in Medicine. The history of how ES cells were first discovered and genetically manipulated highlights the importance of collaboration among scientists from different backgrounds with a shared vision.     

A comparison of calibration methods for stereo fluoroscopic imaging systems

Stereo (biplane) fluoroscopic imaging systems are considered the most accurate and precise systems to study joint kinematics in vivo. Calibration of a biplane fluoroscopy system consists of three steps: (1) correction for spatial image distortion; (2) calculation of the focus position; and (3) calculation of the relative position and orientation of the two fluoroscopy systems with respect to each other. In this study we compared 6 methods for calibrating a biplane fluoroscopy system including a new method using a novel nested-optimization technique. To quantify bias and precision, an electronic digital caliper instrumented with two tantalum markers on radiolucent posts was imaged in three configurations, and for each configuration placed in ten static poses distributed throughout the viewing volume. Bias and precision were calculated as the mean and standard deviation of the displacement of the markers measured between the three caliper configurations. The data demonstrated that it is essential to correct for image distortion when sub-millimeter accuracy is required. We recommend calibrating a stereo fluoroscopic imaging system using an accurately machined plate and a calibration cube, which improved accuracy 2-3 times compared to the other calibration methods. Once image distortion is properly corrected, the focus position should be determined using the Direct Linear Transformation (DLT) method for its increased speed and equivalent accuracy compared to the novel nested-optimization method. The DLT method also automatically provides the 3D fluoroscopy configuration. Using the recommended calibration methodology, bias and precision of 0.09 and 0.05 mm or better can be expected for measuring inter-marker distances.     

A stereo music system as environmental enrichment for captive chimpanzees

Music has been shown to have beneficial effects on humans but little is known about the effects of music on nonhuman primates in biomedical research settings. The authors monitored the effects of music on the behavior of captive chimpanzees and found that music had significant positive effects, including a reduction in agitated and aggressive behaviors.     

A stereo imaging system for measuring structural parameters of plant canopies

Plants constantly adapt their leaf orientation in response to fluctuations in the environment, to maintain radiation use efficiency in the face of varying intensity and incidence direction of sunlight. Various methods exist for measuring structural canopy parameters such as leaf angle distribution. However, direct methods tend to be labour-intensive, while indirect methods usually give statistical information on stand level rather than on individual leaves. We present an area-based, binocular stereo system composed of commercially available components that allows three-dimensional reconstruction of small- to medium-sized canopies on the level of single leaves under field conditions. Spatial orientation of single leaves is computed with automated processes using modern, well-established stereo matching and segmentation techniques, which were adapted for the properties of plant canopies, providing high spatial and temporal resolution (angle measurements with an accuracy of approx. +/-5 degrees and a maximum sampling rate of three frames per second). The applicability of our approach is demonstrated in three case studies: (1) the dihedral leaflet angle of an individual soybean was tracked to monitor nocturnal and daytime leaf movement showing different frequencies and amplitudes; (2) drought stress was diagnosed in soybean by quantifying changes in the zenith leaflet angle distribution; and (3) the diurnal course of the zenith leaf angle distribution of a closed soybean canopy was measured.     

A new method for non-invasive biomass determination based on stereo photogrammetry

Bioprocess and Biosystems Engineering - A novel, non-destructive method for the biomass estimation of biological samples on culture dishes was developed. To achieve this, a photogrammetric system,...     

A cautiously optimistic vision for marker-assisted breeding

Even though marker-assisted selection now plays a prominent role in the field of plant breeding, examples of successful, practical outcomes are rare. It is clear that DNA markers hold great promise, but realizing that promise remains elusive. Despite innovations like better marker systems and improved genetic mapping strategies, most marker associations are not sufficiently robust for successful marker-assisted selection. In large part this is due to inadequate experimental design. Molecular breeders must reassess their research programs so that DNA marker work leads to useful selection tools and valuable germplasm. As molecular breeders adopt more rigorous experimental guidelines and ambitious goals, they also need to integrate the growing body of knowledge from genomics and bioinformatics.     

A nonlinear regularization approach to early vision

We propose a new class of approaches to smooth visual data while preserving significant transitions of these data as clues for segmentation. Formally, the given visual data are represented as a noisy (image) function , and we present a class of continuously formulated global minimization problems to smooth . The resulting function can be characterized as the minimizer of a specific nonquadratic functional or, equivalently, as the result of an associated nonlinear diffusion process. Our approach generalizes the well-known quadratic regularization principle while retaining its attractive properties: For any given , the solution to the proposed minimization problem is unique and depends continuously on the data . Furthermore, convergence of approximate solutions obtained by finite element discretization holds true. We show that the nodal variables of any chosen finite element subspace can be interpreted as computational units whose activation dynamics due to the nonlinear smoothing process evolve like a globally asymptotically stable network. A corresponding analogue implementation is thus feasible and would provide a real time processing stage for the transition preserving smoothing of visual data. Using artificial as well as real data we illustrate our approach by numerical examples. We demonstrate that solutions to our approach improve those obtained by quadratic minimization and show the influence of global parameters which allow for a continuous, scale-dependent, and selective control of the smoothing process. Received: 23 February 1994 / Accepted in revised form: 28 July 1994