Self-calibration and motion recovery from silhouettes with two mirrors

LNCS v. 7724-7727 (pts. 1-4) entitled: Computer vision - ACCV 2012: 11th Asian Conference on Computer Vision ... 2012: revised selected papersThis paper addresses the problem of self-calibration and motion recovery from a single snapshot obtained under a setting of two mirrors. The mirrors are able to show five views of an object in one image. In this paper, the epipoles of the real and virtual cameras are firstly estimated from the intersection of the bitangent lines between corresponding images, from which we can easily derive the horizon of the camera plane. The imaged circular points and the angle between the mirrors can then be obtained from equal angles between the bitangent lines, by planar rectification. The silhouettes produced by reflections can be treated as a special circular motion sequence. With this observation, technique developed for calibrating a circular motion sequence can be exploited to simplify the calibration of a single-view two-mirror system. Different from the state-of-the-art approaches, only one snapshot is required in this work for self-calibrating a natural camera and recovering the poses of the two mirrors. This is more flexible than previous approaches which require at least two images. When more than a single image is available, each image can be calibrated independently and the problem of varying focal length does not complicate the calibration problem. After the calibration, the visual hull of the objects can be obtained from the silhouettes. Experimental results show the feasibility and the preciseness of the proposed approach. © 2013 Springer-Verlag.postprin

Euclidean Structure from N>=2 Parallel Circles: Theory and Algorithms

International audienceOur problem is that of recovering, in one view, the 2D Euclidean structure, induced by the projections of N parallel circles. This structure is a prerequisite for camera calibration and pose computation. Until now, no general method has been described for N > 2. The main contribution of this work is to state the problem in terms of a system of linear equations to solve.We give a closed-form solution as well as bundle adjustment-like refinements, increasing the technical applicability and numerical stability. Our theoretical approach generalizes and extends all those described in existing works for N = 2 in several respects, as we can treat simultaneously pairs of orthogonal lines and pairs of circles within a unified framework. The proposed algorithm may be easily implemented, using well-known numerical algorithms. Its performance is illustrated by simulations and experiments with real images

Non-Parametric Sequential Frame Decimation for Scene Reconstruction in Low-Memory Streaming Environments

Abstract not provide

Visualization of Industrial Structures with Implicit GPU Primitives

International audienceWe present a method to interactively visualize large industrial models by replacing most triangles with implicit GPU primitives: cylinders, cone and torus slices. After a reverse-engineering process that recovers these primitives from triangle meshes, we encode their implicit parameters in a texture that is sent to the GPU. In rendering time, the implicit primitives are visualized seamlessly with other triangles in the scene. The method was tested on two massive industrial models, achieving better performance and image quality while reducing memory use

An automated calibration method for non-see-through head mounted displays

Accurate calibration of a head mounted display (HMD) is essential both for research on the visual system and for realistic interaction with virtual objects. Yet, existing calibration methods are time consuming and depend on human judgements, making them error prone. The methods are also limited to optical see-through HMDs. Building on our existing HMD calibration method [1], we show here how it is possible to calibrate a non-see-through HMD. A camera is placed inside an HMD displaying an image of a regular grid, which is captured by the camera. The HMD is then removed and the camera, which remains fixed in position, is used to capture images of a tracked calibration object in various positions. The locations of image features on the calibration object are then re-expressed in relation to the HMD grid. This allows established camera calibration techniques to be used to recover estimates of the display’s intrinsic parameters (width, height, focal length) and extrinsic parameters (optic centre and orientation of the principal ray). We calibrated a HMD in this manner in both see-through and in non-see-through modes and report the magnitude of the errors between real image features and reprojected features. Our calibration method produces low reprojection errors and involves no error-prone human measurements

Direct Calibration and Data Consistency in 3-D Laser Scanning

This paper addresses two aspects of trian ulation- ased ran e sensors usin structured laser li ht: cali ration and easure ents consistenc . e present a irec ca i ra io techni ue which does not re uire odellin an speci c sensor co ponent or pheno ena, therefore is not li ited in accurac the ina ilit to odel error sources. e also s etch so e co sis e c es s ased on two-ca era eo etr which a e it possi le to ac uire satisfactor ran e i a es of hi hl re ecti e surfaces with holes. peri ental results indicatin the alidit of the ethods are reported. ntro uction This paper addresses two aspects of the acquisition of range data with the popular triangulation-based range sensors using structured laser light [1, 2, 3, 12]: direct calibration and measurement consistency. The commonly adopted model-based calibration estimates the parameters of the geometric transformation that back-projects any points of the image plane of each camera onto the laser plane [1, 2]. This requires a valid closed-f..

Motion recovery for uncalibrated turntable sequences using silhouettes and a single point

LNCS v. 5259 is the conference proceedings of ACIVS 2008This paper addresses the problem of self-calibration and motion recovery for turntable sequences. Previous works exploited silhouette correspondences induced by epipolar tangencies to estimate the image invariants under turntable motion and recover the epipolar geometry. These approaches, however, require the camera intrinsics in order to obtain an Euclidean motion, and a dense sequence is required to provide a precise initialization of the image invariants. This paper proposes a novel approach to estimate the camera intrinsics, the image invariants and the rotation angles from a sparse turntable sequence. The silhouettes and a single point correspondence are extracted from the image sequence. The point traces out a conic in the sequence, from which the fixed entities (i.e., the image of the rotation axis, the horizon, the vanishing point of the coordinates, the circular points and a scalar) can be recovered given a simple initialization of the camera intrinsic matrix. The rotation angles are then recovered by estimating the epipoles that minimize the transfer errors of the outer epipolar tangents to the silhouettes for each pair of images. The camera intrinsics can be further refined by the above optimization. Based on a given range of the initial focal length, a robust method is proposed to give the best estimate of the camera intrinsics, the image invariants, the full camera positions and orientations, and hence a Euclidean reconstruction. Experimental results demonstrate the simplicity of this approach and the accuracy in the estimated motion and reconstruction. © 2008 Springer Berlin Heidelberg.link_to_subscribed_fulltextThe 10th International Conference on Advanced Concepts for Intelligent Vision Systems (ACIVS 2008), Juan-les-Pins, France, 20-24 October 2008. In Lecture Notes in Computer Science, 2008, v. 5259, p. 796-80

Motion Recovery for Uncalibrated Turntable Sequences Using Silhouettes and a Single Point

This paper addresses the problem of self-calibration and motion recovery for turntable sequences. Previous works exploited silhouette correspondences induced by epipolar tangencies to estimate the image invariants under turntable motion and recover the epipolar geometry. These approaches, however, require the camera intrinsics in order to obtain an Euclidean motion, and a dense sequence is required to provide a precise initialization of the image invariants. This paper proposes a novel approach to estimate the camera intrinsics, the image invariants and the rotation angles from a sparse turntable sequence. The silhouettes and a single point correspondence are extracted from the image sequence. The point traces out a conic in the sequence, from which the fixed entities (i.e., the image of the rotation axis, the horizon, the vanishing point of the coordinates, the circular points and a scalar) can be recovered given a simple initialization of the camera intrinsic matrix. The rotation angles are then recovered by estimating the epipoles that minimize the transfer errors of the outer epipolar tangents to the silhouettes for each pair of images. The camera intrinsics can be further refined by the above optimization. Based on a given range of the initial focal length, a robust method is proposed to give the best estimate of the camera intrinsics, the image invariants, the full camera positions and orientations, and hence a Euclidean reconstruction. Experimental results demonstrate the simplicity of this approach and the accuracy in the estimated motion and reconstruction