Showing papers on "Real image published in 1988"

A computational approach to motion perception

Abstract: In this paper it is shown that the computation of the optical flow from a sequence of timevarying images is not, in general, an underconstrained problem. A local algorithm for the computation of the optical flow which uses second order derivatives of the image brightness pattern, and that avoids the aperture problem, is presented. The obtained optical flow is very similar to the true motion field -- which is the vector field associated with moving features on the image plane -- and can be used to recover 3D motion information. Experimental results on sequences of real images, together with estimates of relevant motion parameters, like time-to-crash for translation and angular velocity for rotation, are presented and discussed. Due to the remarkable accuracy which can be achieved in estimating motion parameters, the proposed method is likely to be very useful in a number of computer vision applications.

Stereo disparity computation using Gabor filters

Abstract: A solution to the correspondence problem for stereopsis is proposed using the differences in the complex phase of local spatial frequency components. One-dimensional spatial Gabor filters (Gabor 1946; Marcelja 1980), at different positions and spatial frequencies are convolved with each member of a stereo pair. The difference between the complex phase at corresponding points in the two images is used to find the stereo disparity. Disparity values are combined across spatial frequencies for each image location. Three-dimensional depth maps have been computed from real images under standard lighting conditions, as well as from random-dot stereograms (Julesz 1971). The algorithm can discriminate disparities significantly smaller than the width of a pixel. It is possible that a similar mechanism might be used in the human visual system.

Structural stereopsis for 3-D vision

Abstract: A novel approach to solving the stereo correspondence problem in computer vision is described. Structural descriptions of two two-dimensional views of a scene are extracted by one of possibly several available low-level processes, and a new theory of inexact matching for such structures is derived. An entropy-based figure of merit for attribute selection and ordering is defined. Experimental results applying these techniques to real image pairs are presented. Some manipulation experiments are briefly presented. >

Detecting Specular Reflections Using Lambertian Constraints

Abstract: Specularities-briglit image regions formed by specular reflectioir-are likely to be mistalien for genuine surface ma,rking.j by processes that perform photometric analysis, derive motion fields from optical flow or estimate depth from binocular stereo. In addit8iori they can be uscd to infer surface geometry. This paper describes a scheme for detecting specularities based 011 a cliaracterisatioil of Larnbertian surfaces. Real surfaces are not simple composites of Lambertiaii and specular sur- faces hut evidence suggests that away from specrilnrities they do not deviate from the Lainbertian model by more than a factor of 3 or so. This proves adequate to serve as a constraint for specularity detection. Two independent tests identify iinage regions where tlie constraint is violated. Tlie detector is shown to performs well on a varicty of real images. Applications: improving binocular stereo and inferring surface geometry are described using specularities produced by the detector. ACI(NOWLEI)GEI\IENTS: Work done at:L)ept. Conip. Sci, TJniv. Edin- burgh; Studenthip: (gjh) IDM UKSC & SERC; Grant Pics: AIVRU Sliefield; IIelp: A.Zisserinan&C.hlarinos.

Real image holographic stereograms

Abstract: Methods and devices for recording and projecting holographic stereograms are disclosed. In one aspect of the invention, a concave semi-cylindrical ("alcove") display system is disclosed in which an image is projected in front of the alcove. The display system provides a very wide angle of view approaching 180 degrees (compared to the 30 degrees of a typical flat hologram) that allows the viewer to look around most of the image content. This type of display is particularly useful in computer aided design projects where designers wish to present an overall three-dimensional display of their work. In another aspect of the invention, a holographic printer and procedures for recording a stereogram are disclosed as well as techniques for producing "predistorted" images for the sub-holograms. A digital processing technique is disclosed which effectively predistorts the source two-dimensional image set for the stereogram to compensate for the effects of the display geometry. This predistortion technique relies upon anamorphic ray tracing. A crossed slit model for the holographic optical system is used to determine the direction and origin of the rays of light from which each sub-hologram of the stereogram is made.

Constraints on length and angle

Abstract: Given a perspective projection of line segments on the image plane, the constraints on their 3D positions and orientations are derived on the assumption that their true lengths or the true angles they make are known. The approach here is first to transform images of line segments to the center of the image plane as if the camera were rotated to aim at them. The 3D information extracted in this canonical position is then transformed back to the original configuration. Examples are given, by using real images, for analytical 3D recovery of a rectangular corner and a corner with two right angles.

Using Flow Field Divergence For Obstacle Avoidance: Towards Qualitative Vision

Abstract: The use of certain measures of flow field divergenee is investigated as a qualitative cue for obstacle avoidance during visual navigation. It is shown that a quantity termed the directional divergence of the 2-D motion field can be used as a reliable indicator of the presence of obstacles in the visual field of an observer undergoing generalized rotational and translational motion. Moreover, the necessary measurements can be robustly obtained from real image sequences. A procedure for robustly extracting divergence information from image sequences which can be performed using a highly parallel architecture is described. Experimental results are presented showing that the system responds as expected to divergence in real world image sequences, and the use of the system to navigate between obstacles is demonstrated.

The transient detection microscope

Abstract: We describe a microscope that preferentially displays moving objects. This all-optical device operates in real-time using the nonlinear coupling of optical beams in a photorefractive crystal of barium titanate. A holographic image is continuously written and compared with the real image, and any discrepancy between the two images is immediately visible. The device can be used to highlight moving objects, such as protozoans, while suppressing the image of any stationary objects in the background. The device needs only milliwatts of laser power, and can detect objects moving at velocities of a few micrometres per second.

Using Symmetries For Analysis Of Shape From Contour

Abstract: Inference of 3-D shape from 2-D contours in a single image is an important problem in machine vision. We survey classes of techniques proposed in the past and provide a critical analysis. We propose two kinds of symmetries in figures, which we call parallel and mirror symmetries, give significant information about surface shape for a variety of objects. We show the constraints imposed by these symmetries and how to use them to infer 3-D shape. Our method is applicable to any zero-gaussian curvature surface, and also to a variety of doubly curved surfaces. One of our mathematical results is that for a cone, the surface shape can be constructed uniquely under very simple assumptions. We also show some preliminary results on extraction of symmetries from real images.

Interactive image projection apparatus

Abstract: An interactive image projection apparatus for the projection of computer generated images on a projection surface in cooperation with a light source and projection optics for projecting a beam of light from the light source onto the projection surface The apparatus includes a substantially transparent image display device disposed in the beam of light and including means for receiving image-defining signals from a computer and producing an image based on the image-defining signals that is projected onto the projection surface in the beam of light A touch screen, at least a portion of which is substantially transparent, is disposed in the beam of light between the image display device and the projection surface and includes means for generating a signal when touched for use as input information at the computer Preferably, the touch screen is supported directly over the image display device The signal from the screen may be used to modify the projected image to facilitate interaction in a convenient manner which promotes the interest and maintains the attention of persons viewing the image

A New Stochastic Model-Based Image Segmentation Technique For X-Ray CT Image

Abstract: This manuscript demonstrates that X-ray CT image can be modeled by a finite normal mixture. The number of image classes in the observed image is detected by the information criteria (AIC or MDL). Parameters of the model are estimated by a modified K-mean algorithm and Bayesian decision criterion is the basis for this image segmentation approach. The use of simulated and real image data demonstrate the very promising results of this proposed technique.

Image information recognition apparatus

Abstract: In an image information recognition apparatus image information read by an image reader is stored in an image memory. Since the read image information corresponds to the entire reading range of the reader, an edge of a specific region of the image signals is detected by an edge detector. Boundaries of the region are determined by a coordinate emulator in accordance with a detection signal from the edge detector. Image information within the region surrounded by the boundaries is read out from the image memory, and a bit mover rotates the image information to a normal position or trims it, as needed.

Shape from patterns: Regularization

Abstract: We present a theory for the recovery of the shape of a surface covered with small elements (texels). The theory is based on the apparent surface-pattern distortion in the image and fits the regularization paradigm, recently introduced in computer vision by Poggio et al., [1985]. A mapping is defined on the basis of measurement of the local distortions of a repeated unknown texture pattern due to the image projection. From this, a constraint on the gradient orientation is determined from the apparent area of a texture element. The analysis is done under an approximation of the perspective projection called paraperspective. The resulting algorithm is applied to several synthetic and real images to demonstrate its performance.

Projection-based high accuracy measurement of straight line edges

Abstract: We present a novel projection-based high accuracy algorithm to determine the parameters of a straight edge in a noisy image. Our algorithm is equivalent to applying a set of very long directional operators over a range of finely quantized angles. This is known to improve both signal-to-noise ratio and localization in the measurement of straight line edges, but was rarely used in practice because of the expense and coefficient restrictions of the operators. The algorithm is implemented by taking a set of projections of the original grey level image, filtering the projections, and analyzing the peaks in projection space to estimate line offset and angle. It also includes a procedure to analyze the peaks in projection space which provides an accuracy better than the quantization in offset and angle parameters. The algorithm was tested on synthetic and a large number of real images and offers very high (subpixel) offset and angular accuracy. The advantages of the algorithm over traditional approaches are improved signal-to-noise ratio and localization accuracy (due to the effective use of very long directional edge operators), no need for expensive edge operators and related hardware, and no need for sophisticated thresholding of the gradient image for finding edges. It is robust in the presence of many types of texture, patterned and bias noise, light intensity, and focus change, and is ideal for use in industrial machine vision, where a large number of parts with straight edges are processed.

Portable image scanner

Abstract: Reflected image light obtained by illuminating a reading portion to be read on a given objective image plane is sent to an image sensor located on the rear side through a reflecting member disposed substantially just above the reading portion. By forming a viewing path inclined forward against the image sensor so as to permit the reading portion to be observed easily, the desired image light reflected from the reading portion is little interfered with external light entering inside the scanner through the viewing path, thereby to enjoy image processing of high quality.

Optical system for compensating chromatic abherration of image

Abstract: An optical system comprises an image deflector having a variable refraction angle for forcibly moving an object image formed by an objective lens onto an image plane, and an aberration suppressor linked to the image deflector for suppressing a chromatic aberration developed in the object image due to the light refraction by the image deflector.

A contour detection algorithm based on the minimum radial inertia (MRI) criterion

Abstract: A new method for contour detection of objects in images is presented. It works simultaneously on all the pixels of real images, in which the object of interest has a radially connected contour. As a consequence, the contour can be described as a linear combination of periodic basic (cubic) splines in polar coordinates. To this aim, the “radial inertia” defined versus a generic radially connected curve, is introduced as a functional over the “significant” pixels of the image. The minimization of this functional supplies the required contour. If necessary, some iterations of the method allow the distortion effects due to extraneous structures and noise to be reduced. Several examples show the capabilities of the proposed method in practical cases.

Underwater hologrammetry: aberrations in the real image of an underwater object when replayed in air

Abstract: The use of holography in the optical inspection and measurement of three-dimensional objects, now known as hologrammetry, places considerable emphasis on geometric precision and high resolution in the reconstructed real image. A discussion of the factors which dictate image fidelity in reconstruction must include an assessment of potential sources of optical aberration. In this paper the authors consider the aberrations introduced when the refractive index of the medium in which the subject is located differs from that in which the real image is replayed, addressing specifically their quantitative evaluation in relation to underwater hologrammetry.

Method of determining the trajectory of a body suitable for moving along a portion of a path, and apparatus for implementing the method

Abstract: A method of determining the trajectory of a body (1) such as a vehicle body on a relatively plane path portion (2), the method being characterized in that it consists: in forming a main real image (4) of the path portion in a plane (19) at a non-zero angle (5) with the path portion; in decomposing said main image as formed into a plurality of points (21); in determining the relationship between the size of a unit length (30) taken substantially at the level of the path portion and the size of its image formed in the main image the size being a function of the number of points covered by the image and of the location of the unit length on said path portion; in determining a secondary image (32) in the main image, the secondary image corresponding to a longitudinal reference mark (31) related to the vehicle on the path portion; and in determining the various successive positions (32, 33, 34) of the secondary image by correlation of the number of points covered by the secondary image, given that the secondary image corresponds, according to the relationship, to a length which is constant on the path portion.

Vehicle head-up display

Abstract: In the display, in which a real image is represented by means of a lens and the windscreen, which follows in the beam path, as a virtual image in the field of view of the vehicle user, the real image and the lens are arranged at the upper rim of the windscreen. Only a mirror element is located in the region of the surface of the dashboard between the lens and the windscreen. This mirror element requires relatively little space, and because of the relatively large distance from the lens element is capable of adjusting the virtual image impinging on the eye of the vehicle user to the respective conditions.

Robust depth estimation from optical flow

Abstract: A robust method for obtaining dense depth-maps from a sequence of noisy intensity images (obtained by a moving camera is presented. Controlled camera motion is exploited to reduce the complexity of the optical flow solution to closed-form. It is well known that optical flow computations suffer from high noise sensitivity. Tensor-product smoothing splines are employed to construct a 3-D continuous approximation to the time-varying intensity data which serves to reduce the effects of noise and restore the properties of continuous optical flow. Spatial and temporal derivative estimates obtained from the 3-D spline approximation are used to compute the depth. Unreliable depth estimates are discarded based on the temporal rate of change of intensity. The effectiveness of the smoothing spline approximation coupled with the efficiency of tensor products and the closed form solution for depth leads to a robust method for obtaining dense depth maps with low computational cost. Experimental results are presented which demonstrate the robustness of the method applied to real image data. These experiments indicate an average relative error of 3.7 percent in the depth measurement is obtainable using a sequence of seven 8-bit quantized images. Suggestions for further improvements in the quality of the depth maps by adjusting the parameters of the smoothing spline are discussed.

Image-reproducing arrangement for motor vehicles including lens means forming a real image adjacent an upper edge of a windshield to which an instrument panel mirror reflects to form a virtual image

Abstract: An image-reproducing arrangement for motor vehicles, in which a real image is represented as virtual image in the field of vision of the vehicle user by means of a lens and the windshield following the lens in the path of the light rays; the real image and the lens are thereby arranged at the upper edge of the windshield. Only a mirror element is located between the lens and the windshield within the area of the surface of the instrument panel. This mirror element requires a relatively small amount of space and by reason of the relatively large distance from the lens element offers the possibility to match the virtual image falling into the eye of the vehicle user to the respective prevailing conditions.

On-line object feature extraction for multispectral scene representation

Abstract: A new on-line unsupervised object-feature extraction method is presented that reduces the complexity and costs associated with the analysis of the multispectral image data and data transmission, storage, archival and distribution. The ambiguity in the object detection process can be reduced if the spatial dependencies, which exist among the adjacent pixels, are intelligently incorporated into the decision making process. The unity relation was defined that must exist among the pixels of an object. Automatic Multispectral Image Compaction Algorithm (AMICA) uses the within object pixel-feature gradient vector as a valuable contextual information to construct the object's features, which preserve the class separability information within the data. For on-line object extraction the path-hypothesis and the basic mathematical tools for its realization are introduced in terms of a specific similarity measure and adjacency relation. AMICA is applied to several sets of real image data, and the performance and reliability of features is evaluated.

Spatio-temporal analysis for velocity estimation of contours in an image sequence with occlusion

Abstract: A method is presented for analyzing a sequence of closely sampled images, forming a spatio-temporal volume. It is proposed to find the normal velocity component of each edge point by making assumptions about this scene, such as smooth motion, common motion and constant illumination. The resulting normal velocity field can then be used to resolve the real velocity field and to perform segmentation. The system is quite robust and is capable of handling occlusion as well as disocclusion. Results are presented on synthetic data consisting of two objects moving with occlusion and on real image sequences. >

Object cues for model-based image interpretation

Abstract: This paper is concerned with generating object cues from grey-level images for use in model-based image interpretation. We describe the idea of local grey-level symmetry and illustrate how points in the grey-level image with this property form local axes of symmetry. These axes together with appropriate scale information form the object cues. The degree of local symmetry in the grey-level image is made explicit by introducing a Centre of Gravity filter. The local axes of symmetry are shown to appear in the centre of gravity image as troughs and a method for labelling the troughs is described. We give results for real images and make an objective comparison with other published methods.

Electronic photographic printer/enlarger

Abstract: A photographic printer has a image taking means such as a color TV camera which takes an image of each picture of a roll of film which includes different sizes of pictures such as 35 mm full-size and 35 mm half-size picture frames to provide image signals, and a memory for storing the image signals. The image signals are read from the memory and displayed as a negative image in the form of a brightness pattern on a display such as CRT. Image signals for a half-size picture are read out from the memory in a direction perpendicular to that in which image signals of a full-size picture are read out, and interpolated so as to display a negative image magnified as large as an image of a full-size picture.

Image recording apparatus for recording still image and letters without distortion

Abstract: An image recording apparatus displays, together with information, an image represented by video signals read out from a video signal recording medium on a video display so as to project the displayed image and information onto an image recording medium. For the displayed image and the information displayed in the proximity of the image, light is interrupted in the vicinity of edges of areas of the image recording medium where the image and the information are projected. From the image projected onto the image recording medium, a printed picture thereof is attained in which the contour of the image is not distorted and the position thereof is fixed.

Application Of Qualitative Depth And Shape From Stereo

Abstract: Obtaining exact depth from binocular dis- parities is hard if camera calibration is needed. We will show that qualitative depth and shape information can be obtained from stereo disparities with almost no computations, and with no prior knowledge (or computation) of camera's parameters. First, we derive two expressions that order matched points in the images in two distinct depth-consistent ways from image coor- dinates only. Their use demonstrates some anomalies that have been observed in psychophysical experiments, most notably the "induced size effect". Second, we apply the same approach to estimate some qualitative behavior of the normal to the surface of any object in the field of view. In a similar way we develop an algorithm to compute axes of zero-curvature from disparities alone. The algorithm is shown to be quite robust against viola- tions of the basic assumptions of the computation on synthetic images, with relatively large controlled deviations. It performs almost as well on real images, as demonstrated on an image of four cans at different orientations. In this example, the true zero- curvature axes have been found for three cans, and an estimate with some small error has been found for the fourth.

Method of increasing the brightness of an image and helmet mounted display

Abstract: A helmet mounted display in which a filter (34) receives rays of light at various angles of incidence from an image (40) to be superimposed on the scene being viewed by the operator and reflects these rays to a second surface (32) where the rays are re-reflected through the filter (34) and to the eye (28) of the observer characterized in that the filter is coated in such a manner that it reflects from each position (A-F) on its surface rays from the image that strike at predetermined angles of incidence but which transmits at each position rays which are received from the second surface