Showing papers on "Monocular vision published in 2004"

Difference scaling of gloss: nonlinearity, binocularity, and constancy.

Abstract: Gloss is an attribute of visual appearance that originates from the geometrical distribution of the light reflected by the surface. We used the maximum likelihood difference scaling (MLDS) procedure (L.T. Maloney & J. N. Yang, 2003) to estimate gloss scales over an extended range. Observers' judgments were obtained for a series of 10 black, coated samples for two directions of illumination, in binocular and monocular vision. The results showed a nonlinear relation between gloss percept and instrumental specular gloss values. Sensitivity is higher at extreme scale values than in the middle. In binocular vision, the sensitivity to gloss is higher than in monocular vision exclusively for high gloss levels. Lastly, we found that gloss difference scales, when expressed in terms of the samples rather than the photometric characteristics, vary little with the direction of illumination. Gloss scaling thus seems to be independent of the geometrical variations of the luminous flux at the surface of the sample. By analogy with the term "color constancy," we call this property "gloss constancy."

When two eyes are better than one in prehension: monocular viewing and end-point variance

Abstract: Previous research has suggested that binocular vision plays an important role in prehension. It has been shown that removing binocular vision affects (negatively) both the planning and on-line control of prehension. It has been suggested that the adverse impact of removing binocular vision is because monocular viewing results in an underestimation of target distance in visuomotor tasks. This suggestion is based on the observation that the kinematics of prehension are altered when viewing monocularly. We argue that it is not possible to draw unambiguous conclusions regarding the accuracy of distance perception from these data. In experiment 1, we found data that contradict the idea that a consistent visuomotor underestimation of target distance is an inevitable consequence of monocular viewing. Our data did show, however, that positional variance increases under monocular viewing. We provide an alternative explanation for the kinematic changes found when binocular vision is removed. Our account is based on the changes in movement kinematics that occur when end-point variance is altered following the removal of binocular vision. We suggest that the removal of binocular vision leads to greater perceptual uncertainty (e.g. less precise stimulus cues), resulting in changes in the kinematics of the movement (longer duration movements). Our alternative account reconciles some differences within the research literature. We conducted a series of experiments to explore further the issue of when binocular information is advantageous in prehension. Three subsequent experiments were employed which varied binocular/monocular viewing in selectively lit conditions. Experiment 2 explored the differences in prehension measured between monocular and binocular viewing in a full cue environment with a continuous view of the target object. Experiment 3 required participants to reach, under a monocular or binocular view, for a continuously visible self-illuminated target object in an otherwise dark room. In Experiment 3, the participant could neither see the target object nor the reaching hand following initiation of the prehension movement. Our results suggest that binocular vision contributes to prehension by providing additional information (cues) to the nervous system. These cues appear to be weighted differentially according to the particular constellation of stimulus cues available to the participants when reaching to grasp. One constant advantage of a binocular view appears to be the provision of on-line information regarding the position of the hand relative to the target. In reduced cue conditions (i.e. where a view of the target object is lost following initiation of the movement), binocular information regarding target location appears to be particularly useful in the initial programming of reach distance. Our results are a step towards establishing the specific contributions that binocular vision makes to the control of prehension.

A novel method for resolving vehicle occlusion in a monocular traffic-image sequence

Abstract: This paper presents a novel method for resolving the occlusion of vehicles seen in a sequence of traffic images taken from a single roadside mounted camera. Its concept is built upon a previously proposed vehicle-segmentation method, which is able to extract the vehicle shape out of the background accurately without the effect of shadows and other visual artifacts. Based on the segmented shape and that the shape can be represented by a simple cubical model, we propose a two-step method: first, detect the curvature of the shape contour to generate a data set of the vehicles occluded and, second, decompose it into individual vehicle models using a vanishing point in three dimensions and the set of curvature points of the composite model. The proposed method has been tested on a number of monocular traffic-image sequences and found that it detects the presence of occlusion correctly and resolves most of the occlusion cases involving two vehicles. It only fails when the occlusion was very severe. Further analysis of vehicle dimension also shows that the average estimation accuracy for vehicle width, length, and height are 94.78%, 94.09%, and 95.44%, respectively.

The contribution of stereo vision to one-handed catching

Abstract: Participants with normal (StereoN) and weak (StereoW) stereopsis caught tennis balls under monocular and binocular viewing at three different speed conditions. Monocular or binocular viewing did not affect catching performance in catchers with weak stereopsis, while the StereoN group caught more balls under binocular vision as compared with the monocular condition. These effects were more pronounced with increasing ball speed. Kinematic analysis of the catch partially corroborated these findings. These results indicate that StereoW catchers have not developed a compensatory strategy for information pick-up, and that negative effects of a lack of stereopsis grow larger as temporal constraints become more severe. These findings also support the notion that several monocular and/or binocular information sources can be used in the control of interceptive action.

Dichoptic Visual Masking Reveals that Early Binocular Neurons Exhibit Weak Interocular Suppression: Implications for Binocular Vision and Visual Awareness

Abstract: Visual masking effects are illusions in which a target is rendered invisible by a mask, which can either overlap or not overlap the target spatially and/or temporally. These illusions provide a powerful tool to study visibility and consciousness, object grouping, brightness perception, and much more. As such, the physiological mechanisms underlying the perception of masking are critically important to our understanding of visibility. Several models that require cortical circuits have been proposed previously to explain the mysterious spatial and timing effects associated with visual masking. Here we describe single-unit physiological experiments from the awake monkey that show that visual masking occurs in at least two separate and independent circuits, one that is binocular and one that is monocular (possibly even subcortical), without feedback from higher-level visual brain areas. These and other results together fail to support models of masking that require circuits found only in the cortex, but support our proposed model that suggests that simple ubiquitous lateral inhibition may itself be the fundamental mechanism that explains visual masking across multiple levels in the brain. We also show that area V1 neurons are dichoptic in terms of excitation, but monoptic in terms of inhibition. That is, responses within area V1 binocular neurons reveal that excitation to monocular targets is inhibited strongly only by masks presented to the same eye, and not by masks presented to the opposite eye. These results lead us to redefine the model for the first stage of binocular processing in the visual system, and may be crucial to interpreting the effects of other similar binocular and dichoptic stimulation paradigms, such as the binocular rivalry family of illusions.

Binocular cues and the control of prehension

Abstract: The present study was designed to assess the importance of binocular information (i.e. binocular disparity and angle of convergence) in the control of prehension. Previous studies which have addressed this question have typically used the same experimental manipulation: comparing prehensile movements executed either under binocular conditions to those executed when one eye was occluded (monocular). However this may not be the correct comparison as in addition to depriving the subject of binocular depth cues. it also deprives the subject of any visual information in one eye. Therefore we determined the prehensile performance when the subject viewed the target object and scene with either (i) two different views (binocular), (ii) two identical views (bi-ocular), or (iii) one view only (monocular). Overall, the qualitative and quantitative performance in the bi-ocular and monocular control conditions was very similar on all the main measures (and different from the performance in the binocular condition). We conclude that the deficits in performance observed found for 'monocular' reaches should be attributed to the lack of local depth information specified by the binocular cues. In addition we speculate that convergence angle and binocular disparity, although involved in both the pre-movement and movement-execution phases of the reach, the cues may be weighted differently in both phases of a prehension movement depending on the behavioural strategy involved.

Monocular visual activation patterns in albinism as revealed by functional magnetic resonance imaging.

Abstract: Human albinism is characterized by a disturbance of the chiasmatic projection system leading to predominant representation of just one eye in the contralateral hemisphere. Patients show congenital nystagmus without perceiving oscillopsia. The purpose of the present study was to demonstrate the consequences of atypical chiasmatic crossing with monocular visual stimulation using functional magnetic resonance imaging (fMRI). Sixteen patients with albinism and fifteen normally pigmented controls were stimulated with a monocular visual activation paradigm using flickering checkerboards. In patients, we observed contralaterally dominated activation of visual cortices correlating to clinical albinism parameters. This confirms albinism as a continuous range of hypopigmentation disorders. Additionally, albinos showed activation of the superior colliculus and of visual motion areas although the stimulus was stationary. Activation of visual motion areas is due probably to congenital nystagmus without a conscious correlate like oscillopsia.

Vision-based adaptive cruise control for intelligent road vehicles

Abstract: There is a broad range of robotics technologies that are currently being applied to the generic topic of intelligent transportation systems (ITS). One of the most important research topics in this field is adaptive cruise control (ACC), aiming at adapting the vehicle speed to a predefined value while keeping a safe gap with regard to potential obstacles. For this purpose, a monocular vision system provides the distance between the ego vehicle and the preceding vehicle on the road. The complete system can be understood as a vision-based ACC controller, based on fuzzy logic, which assists the velocity vehicle control offering driving strategies and actuation over the throttle of a car. This controller is embedded in an automatic driving system installed in two testbed mass-produced cars operating in a real environment. The results obtained in these experiments show a very good performance of the vision-based gap controller, which is adaptable to all speeds and safe gap selections.

Depth of Monocular Elements in a Binocular Scene: The Conditions for da Vinci Stereopsis.

Abstract: Quantitative depth based on binocular resolution of visibility constraints is demonstrated in a novel stereogram representing an object, visible to 1 eye only, and seen through an aperture or camouflaged against a background. The monocular region in the display is attached to the binocular region, so that the stereogram represents an object which is only partially visible to the eye that sees it. The results show that this feature is necessary for quantitative depth, which is not found for a fully visible monocular object in the same location, and that depth in these displays, although very precise, is not based on fusional Stereopsis. The findings provide clear support for the existence of a process of da Vinci Stereopsis, but one more sophisticated than the one proposed by K. Nakayama and S. Shimojo (1990).

Automated agricultural equipment navigation using stereo disparity images

Abstract: Visual perception is a key source of information for autonomous navigation of agricultural equipment. Stereoscopic vision improves the monocular vision by adding the third dimension (depth) to attain more accurate object localization within the sensed scene. This research used a compact stereovision camera to find paths from structured agricultural fields to automatically navigate a tractor following crop rows in the field. Stereo disparity was obtained by processing the stereo images of the structured crops. A linear regression method was applied to determine the position of the crop rows from the acquired stereo disparity. A base rule was developed to determine a central path for the tractor based on the resulting crop lines in a window of the interested region within the stereo disparity image. A target point was identified on the central path through stereo analysis, providing critical navigation information. This research proved that stereovision has a great potential for generating navigation information for autonomous agricultural tractors operating in a wide variety of field conditions.

Monocular Vision as a Range Sensor

Abstract: One of the most important abilities for a mobile robot is detecting obstacles in order to avoid collisions. Building a map of these obstacles is the next logical step. Most robots to date have used sensors such as passive or active infrared, sonar or laser range finders to locate obstacles in their path. In contrast, this work uses a single colour camera as the only sensor, and consequently the robot must obtain range information from the camera images. We propose simple methods for determining the range to the nearest obstacle in any direction in the robot’s field of view, referred to as the Radial Obstacle Profile. The ROP can then be used to determine the amount of rotation between two successive images, which is important for constructing a 360o view of the surrounding environment as part of map construction.

Evolution for Monocular Vision Measurement

Abstract: Monocular vision measuring methods are demonstrated, such as geometry analogue method, geometric shape constraint method, structured light method, aided measuring probe(AMP) method and laser aided distance measurement method. The characteristics and principles of structured light method and AMP method are analyzed in detail.

Indoor autonomous navigation using visual memory and pattern tracking

Abstract: The paper deals with autonomous environment mapping, localisation and navigation using exclusively monocular vision and multiple 2D pattern tracking. The environment map is a mosaic of 2D patterns detected on the ceiling plane and used as natural landmarks. The robot is able to reproduce learned trajectories defined by key images representing the visual memory. The pattern tracker is based on particle filetring. It uses both image contours and gray scale level variations to track efficiently 2D patterns on cluttered background. An original observation model used for filter state updating is presented.

Cooperation of passive vision systems in detection and tracking of pedestrians

Abstract: This work presents a cooperative approach for detecting and tracking pedestrians in an urban environment. Its originality lies in the cooperation of two vision systems. A monocular vision system retrieves feature elements and these elements are visualized. However, false detection can occur due to objects whose outline is similar to that of a pedestrian. This problem is solved by the introduction of an auto-adaptive stereovision algorithm that recovers all the vertical 3D segments of the scene. This cooperation supplies a fast and robust method for detecting pedestrian presence. Then, it allows for pedestrian tracking through multiple images.

General design of the lateral control system based on monocular vision on THASV-I

Abstract: In the paper, an intelligent vehicle prototype - THASV-I is designed to study the vehicle active safety on highway environment. The structure features and the relative technologies of the prototype are described. The principle and structure of monocular vision system are described in detail, as well as the lane identification and following algorithm. With some restrictions the monocular vision system can also be used to detect the obstacles in lane before the vehicle. At last, a vision based human-simulating steering control algorithm is presented. The results of the vision based auto-drive experiments on the prototype are also described and analyzed in the paper.

Perception of 3D spatial relations for 3D displays

Abstract: We test perception of 3D spatial relations in 3D images rendered by a 3D display (Perspecta from Actuality Systems) and compare it to that of a high-resolution flat panel display. 3D images provide the observer with such depth cues as motion parallax and binocular disparity. Our 3D display is a device that renders a 3D image by displaying, in rapid succession, radial slices through the scene on a rotating screen. The image is contained in a glass globe and can be viewed from virtually any direction. In the psychophysical experiment several families of 3D objects are used as stimuli: primitive shapes (cylinders and cuboids), and complex objects (multi-story buildings, cars, and pieces of furniture). Each object has at least one plane of symmetry. On each trial an object or its "distorted" version is shown at an arbitrary orientation. The distortion is produced by stretching an object in a random direction by 40%. This distortion must eliminate the symmetry of an object. The subject's task is to decide whether or not the presented object is distorted under several viewing conditions (monocular/binocular, with/without motion parallax, and near/far). The subject's performance is measured by the discriminability d ', which is a conventional dependent variable in signal detection experiments.© (2004) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Vision-based multi-person tracking by using MCMC-PF and RRF in office environments

Abstract: We propose a vision-based method for tracking multiple persons with gray-scale image sequence acquired by a monocular vision sensor in cluttered office environments. This method is based on a novel algorithm for acquiring depth of targets with primitive and robust features, position and size of targets. To cope with long-term occlusions caused by both fixed and moving objects, the method memorizes and utilizes history data of targets' state. We employ MCMC-based particle filter (MCMC-PF) to implement such domain knowledge including, interactions between targets, as well as radial reach filter (RRF) to extract objects in noisy gray-scale images. In experiments, the method could track multiple persons reliably, and recover from errors even when it loses sight of targets.

Experience of Monocular Vision in Australia

Abstract: In-depth interviews with 20 people with monocular vision identified a number of themes associated with the impairment, including psychological, psychosocial, physical, vocational, and daily living problems. They also revealed that in many cases, these problems had profound implications for people's adjustment to daily living. The implications of these findings for the delivery of rehabilitation services are discussed. People with monocular vision have no vision in one eye and typical vision in the other eye, with the

A gradient based approach for stereoscopic error concealment

Abstract: Error concealment is an important field of research in image processing. Many methods have been applied to conceal block losses in monocular images. We present a concealment strategy for block loss in stereoscopic image pairs. Unlike the error concealment techniques used for monocular images, the information of the associated image is utilized, i.e., by means of a projective transformation model, pixel values from the associated stereo image are warped to their corresponding positions in the lost block. The stereoscopic depth perception is much less affected in our approach than using monoscopic error concealment techniques.