Constructive updating/downdating of oblique projectors: a generalization of the Gram-Schmidt process

A generalization of the Gram-Schmidt procedure is achieved by providing equations for updating and downdating oblique projectors. The work is motivated by the problem of adaptive signal representation outside the orthogonal basis setting. The proposed techniques are shown to be relevant to the problem of discriminating signals produced by different phenomena when the order of the signal model needs to be adjusted.Comment: As it will appear in Journal of Physics A: Mathematical and Theoretical (2007

Perception and Mitigation of Artifacts in a Flat Panel Tiled Display System

Flat panel displays continue to dominate the display market. Larger, higher resolution flat panel displays are now in demand for scientific, business, and entertainment purposes. Manufacturing such large displays is currently difficult and expensive. Alternately, larger displays can be constructed by tiling smaller flat panel displays. While this approach may prove to be more cost effective, appropriate measures must be taken to achieve visual seamlessness and uniformity. In this project we conducted a set of experiments to study the perception and mitigation of image artifacts in tiled display systems. In the first experiment we used a prototype tiled display to investigate its current viability and to understand what critical perceptible visual artifacts exist in this system. Based on word frequencies of the survey responses, the most disruptive artifacts perceived were ranked. On the basis of these findings, we conducted a second experiment to test the effectiveness of image processing algorithms designed to mitigate some of the most distracting artifacts without changing the physical properties of the display system. Still images were processed using several algorithms and evaluated by observers using magnitude scaling. Participants in the experiment noticed statistically significant improvement in image quality from one of the two algorithms. Similar testing should be conducted to evaluate the effectiveness of the algorithms on video content. While much work still needs to be done, the contributions of this project should enable the development of an image processing pipeline to mitigate perceived artifacts in flat panel display systems and provide the groundwork for extending such a pipeline to realtime applications

A Virtual Testbed for Fish-Tank Virtual Reality: Improving Calibration with a Virtual-in-Virtual Display

With the development of novel calibration techniques for multimedia projectors and curved projection surfaces, volumetric 3D displays are becoming easier and more affordable to build. The basic requirements include a display shape that defines the volume (e.g. a sphere, cylinder, or cuboid) and a tracking system to provide each user's location for the perspective corrected rendering. When coupled with modern graphics cards, these displays are capable of high resolution, low latency, high frame rate, and even stereoscopic rendering; however, like many previous studies have shown, every component must be precisely calibrated for a compelling 3D effect. While human perceptual requirements have been extensively studied for head-tracked displays, most studies featured seated users in front of a flat display. It remains unclear if results from these flat display studies are applicable to newer, walk-around displays with enclosed or curved shapes. To investigate these issues, we developed a virtual testbed for volumetric head-tracked displays that can measure calibration accuracy of the entire system in real-time. We used this testbed to investigate visual distortions of prototype curved displays, improve existing calibration techniques, study the importance of stereo to performance and perception, and validate perceptual calibration with novice users. Our experiments show that stereo is important for task performance, but requires more accurate calibration, and that novice users can make effective use of perceptual calibration tools. We also propose a novel, real-time calibration method that can be used to fine-tune an existing calibration using perceptual feedback. The findings from this work can be used to build better head-tracked volumetric displays with an unprecedented amount of 3D realism and intuitive calibration tools for novice users

Tele-immersive display with live-streamed video.

Tang Wai-Kwan.Thesis (M.Phil.)--Chinese University of Hong Kong, 2001.Includes bibliographical references (leaves 88-95).Abstracts in English and Chinese.Abstract --- p.iAcknowledgement --- p.iiiChapter 1 --- Introduction --- p.1Chapter 1.1 --- Applications --- p.3Chapter 1.2 --- Motivation and Goal --- p.6Chapter 1.3 --- Thesis Outline --- p.7Chapter 2 --- Background and Related Work --- p.8Chapter 2.1 --- Panoramic Image Navigation --- p.8Chapter 2.2 --- Image Mosaicing --- p.9Chapter 2.2.1 --- Image Registration --- p.10Chapter 2.2.2 --- Image Composition --- p.12Chapter 2.3 --- Immersive Display --- p.13Chapter 2.4 --- Video Streaming --- p.14Chapter 2.4.1 --- Video Coding --- p.15Chapter 2.4.2 --- Transport Protocol --- p.18Chapter 3 --- System Design --- p.19Chapter 3.1 --- System Architecture --- p.19Chapter 3.1.1 --- Video Capture Module --- p.19Chapter 3.1.2 --- Video Streaming Module --- p.23Chapter 3.1.3 --- Stitching and Rendering Module --- p.24Chapter 3.1.4 --- Display Module --- p.24Chapter 3.2 --- Design Issues --- p.25Chapter 3.2.1 --- Modular Design --- p.25Chapter 3.2.2 --- Scalability --- p.26Chapter 3.2.3 --- Workload distribution --- p.26Chapter 4 --- Panoramic Video Mosaic --- p.28Chapter 4.1 --- Video Mosaic to Image Mosaic --- p.28Chapter 4.1.1 --- Assumptions --- p.29Chapter 4.1.2 --- Processing Pipeline --- p.30Chapter 4.2 --- Camera Calibration --- p.33Chapter 4.2.1 --- Perspective Projection --- p.33Chapter 4.2.2 --- Distortion --- p.36Chapter 4.2.3 --- Calibration Procedure --- p.37Chapter 4.3 --- Panorama Generation --- p.39Chapter 4.3.1 --- Cylindrical and Spherical Panoramas --- p.39Chapter 4.3.2 --- Homography --- p.41Chapter 4.3.3 --- Homography Computation --- p.42Chapter 4.3.4 --- Error Minimization --- p.44Chapter 4.3.5 --- Stitching Multiple Images --- p.46Chapter 4.3.6 --- Seamless Composition --- p.47Chapter 4.4 --- Image Mosaic to Video Mosaic --- p.49Chapter 4.4.1 --- Varying Intensity --- p.49Chapter 4.4.2 --- Video Frame Management --- p.50Chapter 5 --- Immersive Display --- p.52Chapter 5.1 --- Human Perception System --- p.52Chapter 5.2 --- Creating Virtual Scene --- p.53Chapter 5.3 --- VisionStation --- p.54Chapter 5.3.1 --- F-Theta Lens --- p.55Chapter 5.3.2 --- VisionStation Geometry --- p.56Chapter 5.3.3 --- Sweet Spot Relocation and Projection --- p.57Chapter 5.3.4 --- Sweet Spot Relocation in Vector Representation --- p.61Chapter 6 --- Video Streaming --- p.65Chapter 6.1 --- Video Compression --- p.66Chapter 6.2 --- Transport Protocol --- p.66Chapter 6.3 --- Latency and Jitter Control --- p.67Chapter 6.4 --- Synchronization --- p.70Chapter 7 --- Implementation and Results --- p.71Chapter 7.1 --- Video Capture --- p.71Chapter 7.2 --- Video Streaming --- p.73Chapter 7.2.1 --- Video Encoding --- p.73Chapter 7.2.2 --- Streaming Protocol --- p.75Chapter 7.3 --- Implementation Results --- p.76Chapter 7.3.1 --- Indoor Scene --- p.76Chapter 7.3.2 --- Outdoor Scene --- p.78Chapter 7.4 --- Evaluation --- p.78Chapter 8 --- Conclusion --- p.83Chapter 8.1 --- Summary --- p.83Chapter 8.2 --- Future Directions --- p.84Chapter A --- Parallax --- p.8

Méthodes de rendu à base de vidéos et applications à la réalité Virtuelle

Given a set images of the same scene, the goal of video-based rendering methods is to compute new views of this scene from new viewpoints. The user of this system controls the virtual camera's movement through the scene. Nevertheless, the virtual images are computed from static cameras. A first approach is based on a reconstruction of the scene and can provide accurate models but often requires lengthy computation before visualization. Other methods try to achieve real-time rendering. Our main contribution to video-base rendering concerns the plane sweep method which belongs to the latter family. The plane sweep method divides space in parallel planes. Each point of each plane is processed independently in order to know if it lies on the surface of an object of the scene. These informations are used to compute a new view of the scene from a new viewpoint. This method is well suited to an implementation using graphic hardware and thus to reach realtime rendering. Our main contribution to this method concerns the way to consider whether a point of a plane lies on the surface of an object of the scene. We first propose a new scoring method increasing the visual quality of the new images. Compared with previous approaches, this method implies fewer constraints on the position of the virtaul camera, i.e. this camera does not need to lie between the input camera's area. We also present an adaptation of the plane sweep algorithm that handles partial occlusions. According to video-based rendering practical applications in virtual reality, we propose an improvement of the plane sweep method dealing with stereoscopic images computation that provides visualization of the virtual scene in relief. Our enhancement provides the second view with only low additional computation time whereas most of the others techniques require to render the scene twice. This improvement is based on a sharing of the informations common to the two stereoscopic views. Finally, we propose a method that removes pseudoscopic movements in a virtual reality application. These pseudoscopic movements appear when the observer moves in front of the stereoscopic screen. Then the scene roportions seem to be distorted and the observer sees the objects of the scene moving in an anormal way. The method we propose is available either on a classical stereoscopic rendering method or on the Plane Seep algorithm. Every method we propose widely uses graphic harware through to shader programs and provides real-time rendering. These methods only require a standard computer, a video acquisition device and a powerful enough graphic card. There exists a lot of practicalapplications of the plane sweep method, especially in fields like virtual reality, video games, 3d television or security.Etant donné un ensemble de caméras filmant une même scène, le rendu à base de vidéos consiste à générer de nouvelles images de cette scène à partir de nouveaux points de vue. L'utilisateur a ainsi l'impression de pouvoir déplacer une caméra virtuelle dans la scène alors qu'en réalité, toutes les caméras sont fixes. Certaines méthodes de rendu à base de vidéos coûteuses en temps de calcul se basent sur une reconstruction 3d de la scène et produisent des images de très bonne qualité. D'autres méthodes s'orientent plutôt vers le rendu temps réel. C'est dans cette dernière catégorie que s'inscrit la méthode de Plane Sweep sur laquelle porte la majeure partie de nos travaux. Le principe de la méthode des Plane Sweep consiste à discrétiser la scène en plans parallèles et à traiter séparément chaque point de ces plans afin de déterminer s'ils se trouvent ou non sur la surface d'un objet de la scène. Les résultats obtenus permettent de générer une nouvelle image de la scène à partir d'un nouveau point de vue. Cette méthode est particulièrement bien adaptée à une utilisation optimale des ressources de la carte graphique ce qui explique qu'elle permette d'effectuer du rendu en temps réel. Notre principale contribution à cette méthode concerne la façon d'estimer si un point d'un plan représente la surface d'un objet. Nous proposons d'une part un nouveau mode de calcul permettant d'améliorer le résultat visuel tout en rendant la navigation de la caméra virtuelle plus souple. D'autre part, nous présentons une adaptation de la méthode des Plane Sweep permettant de gérer les occlusions partielles. Compte tenu des applications du rendu à base de vidéos en réalité virtuelle, nous proposons une amélioration des Plane Sweep appliquée à la réalité virtuelle avec notamment la création de paires d'images stéréoscopiques permettant de visualiser en relief la scène reconstruite. Notre amélioration consiste à calculer la seconde vue à moindre coût alors qu'une majorité des méthodes concurrentes sont contraintes d'effectuer deux rendus indépendants. Cette amélioration est basée sur un partage des données communes aux deux vues stéréoscopiques. Enfin, dans le cadre de l'utilisation des Plane Sweep en réalité virtuelle, nous présentons une méthode permettant de supprimer les mouvements pseudoscopiques. Ces mouvements pseudoscopiques apparaissent lorsque l'observateur se déplace devant une image stéréoscopique, il ressent alors une distorsion des proportions de la scène virtuelle et voit les objets se déplacer de façon anormale. La méthode de correction que nous proposons est applicable d'une part à des méthodes classiques de rendu d'images de synthèse et d'autre part à la méthode des Plane Sweep. Toutes les méthodes que nous présentons utilisent largement les possibilités du processeur de la carte graphique à l'aide des shader programs et génèrent toutes des images en temps réel. Seuls un ordinateur grand public, un dispositif d'acquisition vidéo et une bonne carte graphique sont suffisants pour les faire fonctionner. Les applications des Plane Sweep sont nombreuses, en particulier dans les domaines de la réalité virtuelle, du jeu vidéo, de la télévision 3d ou de la sécurité