Defining the Pose of any 3D Rigid Object and an Associated Distance

The pose of a rigid object is usually regarded as a rigid transformation, described by a translation and a rotation. However, equating the pose space with the space of rigid transformations is in general abusive, as it does not account for objects with proper symmetries -- which are common among man-made objects.In this article, we define pose as a distinguishable static state of an object, and equate a pose with a set of rigid transformations. Based solely on geometric considerations, we propose a frame-invariant metric on the space of possible poses, valid for any physical rigid object, and requiring no arbitrary tuning. This distance can be evaluated efficiently using a representation of poses within an Euclidean space of at most 12 dimensions depending on the object's symmetries. This makes it possible to efficiently perform neighborhood queries such as radius searches or k-nearest neighbor searches within a large set of poses using off-the-shelf methods. Pose averaging considering this metric can similarly be performed easily, using a projection function from the Euclidean space onto the pose space. The practical value of those theoretical developments is illustrated with an application of pose estimation of instances of a 3D rigid object given an input depth map, via a Mean Shift procedure

Interpolation de points de vue : approches directe et variationnelle

National audienceNous abordons la problématique d'interpolation de points de vue à partir d'une paire d'images stéréoscopique. Ces techniques comportent généralement 3 étapes : l'estimation des correspondances entre les vues, le dosage des contributions de chaque image dans la vue finale, et le rendu. D'un côté, tandis que l'état de l'art est très vaste dans l'estimation des correspondances, nous trouvons peu de travaux formels analysant quel est le "bon" dosage des contributions lors du mélange des images. D'un autre côté, concernant le rendu de nouveaux points de vue nous identifions deux groupes de méthodes bien distincts, les méthodes "directes", et les méthodes "variationnelles". Nous conduisons une étude pour analyser la performance des facteurs de dosage ainsi que l'impact de la méthode utilisée sur le résultat final obtenu. Nous évaluons ces méthodes sur des scènes lambertiennes et non-lambertiennes afin de voir, dans chaque cas, quel choix est le plus pertinent

Viewpoint Interpolation: Direct and Variational Methods

International audienceWe address the topic of novel view synthesis from a stereoscopic pair of images. The techniques have mainly 3 stages: the reconstruction of correspondences between the views, the estimation of the blending factor of each view for the final view, and the rendering. The state of the art has mainly focused on the correspondence topic, but little work addresses the question of which blending factors are best. The rendering methods can be classified into "direct" methods, defining the final image as a function of the original images, and "variational" methods, where the synthesized image is expressed as the solution minimising an energy. In this paper, we experiment different combinations of the blending factors and the rendering method, in order to demonstrate the effect of these two factors on the final image quality

Systèmes d'acquisition multivues

National audienceMultiview acquisition, the focus of this chapter, relates to the capture of synchronized video data representing different viewpoints of a single scene. In contrast to video surveillance systems, which deploy multiple cameras to visually cover a large scale environment to be monitored with little redundancy, the materials, devices or systems used in multiview acquisition are designed to cover several perspectives of a single, often fairly restricted, physical space and use redundancy in images for specific aims. Depending on the final application, the number, layout and settings of cameras can fluctuate greatly. This chapter will introduce the main camera configurations in a purely video multiview capture context, using notable practical examples and their use. Each time, we will also propose links to databases providing access to media produced by devices within each category.L'acquisition multivues, objet de ce chapitre, concerne la capture de données vidéo synchronisées représentant différents points de vue d'une même scène. \textit{A contrario} des systèmes de vidéosurveillance qui déploient de multiples caméras pour couvrir visuellement avec peu de redondance un espace à surveiller de grande étendue, les matériels, dispositifs ou systèmes ici visés couvrent, depuis plusieurs points de vues, un même espace physique, souvent assez réduit, pour profiter de la redondance des images. Selon les applications visées, le nombre, la disposition et le réglage des caméras peuvent grandement fluctuer. Ce chapitre va présenter les principales configurations de capture multivues purement vidéo en se basant sur des exemples significatifs de réalisations et en indiquant les usages qui en sont faits. A chaque fois, seront proposées des bases de données accessibles permettant au lecteur d'accéder à des médias acquis par des dispositifs relevant de la catégorie étudiée

Tracking with Stereo-vision System for Low Speed Following Applications

International audienceResearch in adaptative cruise control (ACC) is currently one of the most important topics in the field of intelligent transportation systems. The main challenge is to perceive the environment, especialy at low speed. In this paper, we present a novel approach to track the 3-D trajectory and speed of the obstacles and the surrounding vehicles through a stereo-vision system. This tracking method extends the classical patch-based Lucas-Kanade algorithm [9], [1] by integrating the geometric constraints of the stereo system into the motion model: the epipolar constraint, which enforces the tracked patches to remain on the epipolar lines, and the magnification constraint, which links the disparity of the tracked patches to the apparent size of these patches. We report experimental results on simulated and real data showing the improvement in accuracy and robustness of our algorithm compared to the classical Lucas-Kanade tracker

Placement optimal de caméras contraintes pour la synthèse de nouvelles vues

International audienceNous étudions le problème du placement optimal sous contraintes, de plusieurs caméras, pour la synthèse de nouvelles vues. Une telle configuration optimale est définie comme celle qui minimise l'incertitude de projection des pixels des caméras de prise de vue sur la vue à synthétiser. Le rendu de cette vue est souvent précédé d'une phase de reconstruction 3D approximative. Nous dérivons la matrice de covariance associée à l'incertitude sur la géométrie, puis nous propageons l'erreur sur le plan de la nouvelle vue. Nous observons l'influence de l'interoculaire et de la distance focale des caméras sur l'erreur projetée, pour des distributions de points aléatoires à diverses profondeurs

Calibration of a wide angle stereoscopic system

This paper was published in OPTICS LETTERS and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: http://dx.doi.org/10.1364/OL.36.003064. Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law.Inaccuracies in the calibration of a stereoscopic system appear with errors in point correspondences between both images and inexact points localization in each image. Errors increase if the stereoscopic system is composed of wide angle lens cameras. We propose a technique where detected points in both images are corrected before estimating the fundamental matrix and the lens distortion models. Since points are corrected first, errors in point correspondences and point localization are avoided. To correct point location in both images, geometrical and epipolar constraints are imposed in a nonlinear minimization problem. Geometrical constraints define the point localization in relation to its neighbors in the same image, and eipolar constraints represent the location of one point referred to its corresponding point in the other image. © 2011 Optical Society of America.Ricolfe Viala, C.; Sánchez Salmerón, AJ.; Martínez Berti, E. (2011). Calibration of a wide angle stereoscopic system. Optics Letters. 36(16):3064-3067. doi:10.1364/OL.36.003064S306430673616Zhang, Z., Ma, H., Guo, T., Zhang, S., & Chen, J. (2011). Simple, flexible calibration of phase calculation-based three-dimensional imaging system. Optics Letters, 36(7), 1257. doi:10.1364/ol.36.001257Longuet-Higgins, H. C. (1981). A computer algorithm for reconstructing a scene from two projections. Nature, 293(5828), 133-135. doi:10.1038/293133a0Ricolfe-Viala, C., & Sanchez-Salmeron, A.-J. (2010). Lens distortion models evaluation. Applied Optics, 49(30), 5914. doi:10.1364/ao.49.005914Armangué, X., & Salvi, J. (2003). Overall view regarding fundamental matrix estimation. Image and Vision Computing, 21(2), 205-220. doi:10.1016/s0262-8856(02)00154-3Devernay, F., & Faugeras, O. (2001). Straight lines have to be straight. Machine Vision and Applications, 13(1), 14-24. doi:10.1007/pl0001326

Dynamic Stereoscopic Previz

International audienceThe pre-production stage in a film workflow is important to save time during production. To be useful in stereoscopic 3-D movie-making, storyboards and previz tools need to be adapted in at least two ways. First, it should be possible to specify the desired depth values with suitable and intuitive user interfaces. Second, it should be possible to preview the stereoscopic movie with a suitable screen size. In this paper, we describe a novel technique for simulating a cinema projection room with arbitrary dimensions in a real-time game engine, while controling the camera interaxial and convergence parameters with a gamepad controller. Our technique has been implemented in the Blender Game Engine and tested during the shooting of a short movie. Qualitative experimental results show that our technique overcomes the limitations of previous work in stereoscopic previz and can usefully complement traditional storyboards during pre-production of stereoscopic 3-D movies

A fast and Efficient Subpixelic Edge Detector

National audienceIn this article we present a two dimensional edge extractor which gives the edge position in an image with a subpixelic precision. The method presented here gives a good accuracy with a low computational cost, and its implementation is very simple since it is derivated from the well-known Non-Maxima Suppression method [I, 3]. We also justify the method by showing that it gives the exact result in a theoretical one dimensional example. We have tested the edge extractor on several synthetical and real images and the results are reported in this paper