Showing papers on "Monocular vision published in 1996"

Direct computation of shape cues using scale-adapted spatial derivative operators

Abstract: This paper addresses the problem of computing cues to the three-dimensional structure of surfaces in the world directly from the local structure of the brightness pattern of either a single monocular image or a binocular image pair. It is shown that starting from Gaussian derivatives of order up to two at a range of scales in scale-space, local estimates of (i) surface orientation from monocular texture foreshortening, (ii) surface orientation from monocular texture gradients, and (iii) surface orientation from the binocular disparity gradient can be computed without iteration or search, and by using essentially the same basic mechanism. The methodology is based on a multi-scale descriptor of image structure called the windowed second moment matrix, which is computed with adaptive selection of both scale levels and spatial positions. Notably, this descriptor comprises two scale parameters; a local scale parameter describing the amount of smoothing used in derivative computations, and an integration scale parameter determining over how large a region in space the statistics of regional descriptors is accumulated. Experimental results for both synthetic and natural images are presented, and the relation with models of biological vision is briefly discussed.

Accommodation, convergence, pupil diameter and eye blinks at a CRT display flickering near fusion limit.

Abstract: This study investigates possible effects of temporally modulated light stimulation near critical fusion frequency (CFF) when subjects observe a cathode ray tube (CRT) operated at different refresh rates. Various visual functions were measured in a series of tests of 2.5 min duration. In experiment 1, at a repetition rate of 50 Hz mean pupil size was 0.055 mm smaller than at 300 Hz. The precision of convergence and accommodation in binocular vision was not affected. In experiment 2, 300 Hz was compared with the lowest frequency that did not produce visible flicker for each subject. At the lower rate (55 to 90 Hz), mean accommodation in monocular vision was 0.06 D weaker, median eye blink duration was 6% shorter, and mean eye blink interval was 15% longer. Individual differences and possible fatigue effects of intermittent light at visual display units are discussed.

Binocular visual surface perception

Abstract: Binocular disparity, the differential angular separation between pairs of image points in the two eyes, is the well-recognized basis for binocular distance perception. Without denying disparity's role in perceiving depth, we describe two perceptual phenomena, which indicate that a wider view of binocular vision is warranted. First, we show that disparity can play a critical role in two-dimensional perception by determining whether separate image fragments should be grouped as part of a single surface or segregated as parts of separate surfaces. Second, we show that stereoscopic vision is not limited to the registration and interpretation of binocular disparity but that it relies on half-occluded points, visible to one eye and not the other, to determine the layout and transparency of surfaces. Because these half-visible points are coded by neurons carrying eye-of-origin information, we suggest that the perception of these surface properties depends on neural activity available at visual cortical area V1.

Monocular mechanisms determine plaid motion coherence

Abstract: Although the neural location of the plaid motion coherence process is not precisely known, the middle temporal (MT) cortical area has been proposed as a likely candidate. This claim rests largely on the neurophysiological findings showing that in response to plaid stimuli, a subgroup of cells in area MT responds to the pattern direction, whereas cells in area V1 respond only to the directions of the component gratings. In Experiment 1, we report that the coherent motion of a plaid pattern can be completely abolished following adaptation to a grating which moves in the plaid direction and has the same spatial period as the plaid features (the so-called "blobs"). Interestingly, we find this phenomenon is monocular: monocular adaptation destroys plaid coherence in the exposed eye but leaves it unaffected in the other eye. Experiment 2 demonstrates that adaptation to a purely binocular (dichoptic) grating does not affect perceived plaid coherence. These data suggest several conclusions: (1) that the mechanism determining plaid coherence responds to the motion of plaid features, (2) that the coherence mechanism is monocular, and thus (3), that it is probably located at a relatively low level in the visual system and peripherally to the binocular mechanisms commonly presumed to underlie two-dimensional (2-D) motion perception. Experiment 3 examines the spatial tuning of the monocular coherence mechanism and our results suggest it is broadly tuned with a preference for lower spatial frequencies. In Experiment 4, we examine whether perceived plaid direction is determined by the motion of the grating components or the features. Our data strongly support a feature-based model.

Human Body Tracking by Monocular Vision

Abstract: This article describes a tracking method of 3D articulated complex objects (for example, the human body), from a monocular sequence of perspective images. These objects and their associated articulations must be modelled. The principle of the method is based on the interpretation of image features as the 3D perspective projections points of the object model and an iterative Levenberg-Marquardt process to compute the model pose in accordance with the analysed image.

Binocular night vision goggles, where one ocular could be moved from the beam path

Abstract: The invention relates to a compact night observation viewer (Fig. 1) with one light amplifier (1) and amongst others two eyepieces (13A/B) in the horizontal plane under the input aperture (20), and where one eyepiece (13A) can be folded out of the beam path (Fig. 3) so that a free through-view passage is opened through the viewer, whereby the observed scene can also be observed without light amplification. The invention solves thereby the problem of how in a technically and economically satisfactory way it is able to freely change between binocular and monocular vision. As an addition and optionally, the invention permits the distance between the two eyepieces to become adjustable and that a teleconverter (Fig. 3) can be applied in front of the light amplifier input (20) and possibly also in above described free through-view opening so that magnification can be switched (Fig. 4) both with and without light amplification.

Differentiation of VEP intermodulation and second harmonic components by dichoptic, monocular, and binocular stimulation

Abstract: Modulation by two temporal frequencies differentiates visual processing at the fundamentals (1Fs), second harmonics (2Fs), and second-order intermodulation components (IMCs), the latter created neurally as the sum or difference of the two modulation frequencies. Steady-state VEPs were recorded while stereo-normal adults viewed luminance or grating stimuli modulated by up to three temporal frequencies under dichoptic, monocular, or ordinary (binocular) viewing conditions arranged using liquid crystal light shutters. In Experiment 1, modulation of luminance by a single temporal frequency produced strong 1F and 2F VEP components, but modulation of gratings produced only 2Fs. Modulation by two temporal frequencies resulted in IMCs, often in the absence of evoked activity in the EEC at the 1Fs. IMCs were generally larger during pattern as compared to luminance modulation. Amplitudes of 1Fs and IMCs were smaller, but 2Fs were larger, during dichoptic as compared to ordinary viewing. Although the 2F to a single modulation presented to one eye was not reduced when a second frequency was added to the opposite eye, monocular IMCs were diminished when a frequency was added to the opposite eye. We conclude that 2Fs and IMCs are associated with different neural substrates. Results are consistent with a two pathway model with one pathway having a nonlinear filter prior to binocular combination, the other pathway having a nonlinearity following binocular linear summation. Implications of these data for binocular function are discussed.

Dynamic vision for ROV stabilization

Abstract: Stationkeeping is an important capability for various functions involving the operation of undersea vehicles. This involves an accurate estimation of the vehicle displacement. In this paper we propose a monocular vision system for determining the motion of an underwater remotely operated vehicle. The camera motion is estimated with a feature-based method which requires the extraction and the matching of relevant features. The performance of the algorithm is presented with simulated and synthetic images.

Recovering Generalized Cylinders by Monocular Vision

Abstract: In this paper, we propose a theoretical study of the Generalized Cylinders (GC) with constant circular cross-section viewed under perspective projection.

Curved surface reconstruction using monocular vision

Abstract: In monocular vision, a priori knowledge is necessary to perform 3D reconstruction. This paper describes how to evaluate two out of six external parameters of a camera in order to project an image on a curved surface (generalized cylinder). The final aim consists of reconstructing the model of the surface. Afterwards, with this model we can derive a flat representation of the scene without any distortions due to the projective geometry. In this work based on one projected view of the scene, we develop two methods to detect the projection of the revolution axis of the curved surface. With this axis, we can then extract the external parameters of a camera. The first one is based on the derivation of a polynomial function and the second one is based on the detection of the common normal between curves.

Case studies of a new approach using partial and selective occlusion for the clinical treatment of diplopia.

Abstract: Diplopia is a serious and intolerable sequelae to the problems of strabismus, ophthalmoplegia, gaze palsy, and decompensated binocular skills that occur in patients with head injury, stroke and other neurologically compromising conditions. A variety of treatment measures are available for diplopia, but they are not always successful. When treatment is either not used, or fails, patching has been used to occlude the vision of one eye. Although patching is effective in eliminating diplopia, it creates problems by rendering the patient monocular. Monocular vision causes a loss of stereopsis and reduction of peripheral visual field which in turn causes problems in eye hand coordination, depth judgments, orientation, balance, and mobility. A new method of treating diplopia, the 'spot patch', has been successfully evaluated. It is a procedure that eliminates diplopia without the limitations and side effects of traditional patching.

Binocular vision planning with anthropomorphic features for grasping parts by robots

Abstract: Planning of an active vision having anthropomorphic features, such as binocularity, foveas and gaze control, is proposed. The aim of the vision is to provide robots with the pose informaton of an adequate object to be grasped by the robots. For this, the paper describes a viewer-oriented fixation point frame and its calibration, active motion and gaze control of the vision, disparity filtering, zoom control, and estimation of the pose of a specific portion of a selected object. On the basis of the importance of the contour information and the scheme of stereo vision in recognizing objects by humans, the occluding contour pairs of objects are used as inputs in order to show the proposed visual planning.

Binocular correspondence in stereoscopic vision

Abstract: For binocular stereoscopic vision to be possible, the visual nervous system needs to perform two tasks with the information available from the left and right eyes. First, features visible from the left eye must be paired up with the corresponding feature as seen from the right eye's vantage point. Second, the geometric information from the matched binocular features must be transformed into an estimate of binocular disparity. In this sense, the paper by Barlow, Blakemore and Pettigrew1 represents the first complete proposal for the neural mechanisms underlying binocular correspondence and the per­ception of stereoscopic depth. They proposed that the feature selectivity of visually-responsive neurons should have a central role in sorting out which visual features in the left eye should match with those in the right eye and that the same group of neurons should provide signals from which binocular disparity could be extracted to signal depth. In short, for the cat's visual system, the neurons in cortical area VI were proposed to be involved in both binocular matching and the recovery of stereoscopic depth. Neurons in VI have a number of obvious monocular feature selectivities that can be exploited for binocular matching, namely the local orientation, spatial frequency and spatial phase of regions of the image's luminance (black/white) contrast. The beha­vioural significance of these features is also con­firmed by numerous psychophysical studies of the stereoscopic capabilities of human vision. Other feature selectivities in VI, such as colour, may have

On the horopter and Hering-Hillebrand deviation

Abstract: We discuss the usage of Hering-Hillebrand deviation H in depth perception, be it machine vision or human vision.

Detection of obstacle from monocular vision based on histogram matching method

Abstract: This paper proposes a detection method of an unknown obstacle trespassing upon the field of view from a monocular vision installed in an autonomous land vehicle which moves in the unknown static environment. Taking account of the motion restriction of the vehicle, we investigate the vanishing point of motion and the direction of each optical flow as the motion vector observed on a 2D-image. Then, in the case of no obstacles, it is shown that the vector field forms a uniform radial configuration centered at the vanishing point of motion. In this paper, the obstacle detection is performed by extracting a certain disturbed region in the vector field caused by the trespassing obstacle. The normalized histogram matching method suitable for obtaining the vector field is introduced. The experimental result for the real images in the case of an obstacle trespassing upon the field of view is shown.

Computer vision -- ECCV '96 : 4th European Conference on Computer Vision, Cambridge, UK, April 15-18, 1996 : proceedings

Abstract: Colour constancy for scenes with varying illumination.- Color angular indexing.- Bidirectional reflection distribution function expressed in terms of surface scattering modes.- Generalizing Lambert's Law for smooth surfaces.- Local scale control for edge detection and blur estimation.- Regularization, scale-space, and edge detection filters.- Direct differential range estimation using optical masks.- Generalised epipolar constraints.- Object models from contour sequences.- Directions of motion fields are hardly ever ambiguous.- Euclidean reconstruction: From paraperspective to perspective.- Optical flow and phase portrait methods for environmental satellite image sequences.- Refinement of optical flow estimation and detection of motion edges.- Reliable extraction of the camera motion using constraints on the epipole.- Accuracy vs. efficiency trade-offs in optical flow algorithms.- Rigorous bounds for two-frame structure from motion.- The rank 4 constraint in multiple (?3) view geometry.- Using singular displacements for uncalibrated monocular visual systems.- Duality of multi-point and multi-frame geometry: Fundamental shape matrices and tensors.- On the appropriateness of camera models.- Ground plane motion camera models.- Snakes and splines for tracking non-rigid heart motion.- Local quantitative measurements for cardiac motion analysis.- Application of model based image interpretation methods to diabetic neuropathy.- Global alignment of MR images using a scale based hierarchical model.- Reconstruction of blood vessel networks from x-ray projections and a vascular catalogue.- Combining multiple motion estimates for vehicle tracking.- Visual surveillance monitoring and watching.- A robust active contour model for natural scene contour extraction with automatic thresholding.- A maximum-likelihood approach to visual event classification.- Measures for silhouettes resemblance and representative silhouettes of curved objects.- Real-time lip tracking for audio-visual speech recognition applications.- Matching object models to segments from an optical flow field.- Quantification of articular cartilage from MR images using active shape models.- Direct methods for self-calibration of a moving stereo head.- Dense reconstruction by zooming.- Telecentric optics for computational vision.- Recognition, pose and tracking of modelled polyhedral objects by multi-ocular vision.- Locating objects of varying shape using statistical feature detectors.- Generation of semantic regions from image sequences.- Tracking of occluded vehicles in traffic scenes.- Imposing hard constraints on soft snakes.- X Vision: Combining image warping and geometric constraints for fast visual tracking.- Human body tracking by monocular vision.- Computational perception of scene dynamics.- A filter for visual tracking based on a stochastic model for driver behaviour.- Elastically adaptive deformable models.- Statistical feature modelling for active contours.- Motion deblurring and super-resolution from an image sequence.- Uncalibrated visual tasks via linear interaction.- Finding naked people.- Acquiring visual-motor models for precision manipulation with robot hands.- A system for reconstruction of missing data in image sequences using sampled 3D AR models and MRF motion priors.- Elimination of specular surface-reflectance using polarized and unpolarized light.- Separating real and virtual objects from their overlapping images.- Goal-directed video metrology.- Reconstructing polyhedral models of architectural scenes from photographs.- Algebraic varieties in multiple view geometry.- 3D model acquisition from extended image sequences.- Computing structure and motion of general 3D curves from monocular sequences of perspective images.- A factorization based algorithm for multi-image projective structure and motion.