Composition of texture atlases for 3D mesh multi-texturing

We introduce an automatic technique for mapping onto a 3D triangle mesh, approximating the shape of a real 3D object, a high resolution texture synthesized from several pictures taken simultaneously by real cameras surrounding the object. We create a texture atlas by first unwrapping the 3D mesh to form a set of 2D patches with no distortion (i.e., the angles and relative sizes of the 3D triangles are preserved in the atlas), and then mixing the color information from the input images, through another three steps: step no. 2 packs the 2D patches so that the bounding canvas of the set is as small as possible; step no. 3 assigns at most one triangle to each canvas pixel; finally, in step no. 4, the color of each pixel is calculated as a smoothly varying weighted average of the corresponding pixels from several input photographs. Our method is especially good for the creation of realistic 3D models without the need of having graphic artists retouch the texture. Categories and Subject Descriptors (according to ACM CCS): Computer Graphics [1.3.7]: Three-Dimensional Graphics and Realism—Color, shading, shadowing, and textur

ITEM: Inter-Texture Error Measurement for 3D Meshes

We introduce a simple and innovative method to compare any two texture maps, regardless of their sizes, aspect ratios, or even masks, as long as they are both meant to be mapped onto the same 3D mesh. Our system is based on a zero-distortion 3D mesh unwrapping technique which compares two new adapted texture atlases with the same mask but different texel colors, and whose every texel covers the same area in 3D. Once these adapted atlases are created, we measure their difference with ITEM-RMSE, a slightly modified version of the standard RMSE defined for images. ITEM-RMSE is more meaningful and reliable than RMSE because it only takes into account the texels inside the mask, since they are the only ones that will actually be used during rendering. Our method is not only very useful to compare the space efficiency of different texture atlas generation algorithms, but also to quantify texture loss in compression schemes for multi-resolution textured 3D meshes

Multi-Resolution Texture Coding for Multi-Resolution 3D Meshes

We present an innovative system to encode and transmit textured multi-resolution 3D meshes in a progressive way, with no need to send several texture images, one for each mesh LOD (Level Of Detail). All texture LODs are created from the finest one (associated to the finest mesh), but can be re- constructed progressively from the coarsest thanks to refinement images calculated in the encoding process, and transmitted only if needed. This allows us to adjust the LOD/quality of both 3D mesh and texture according to the rendering power of the device that will display them, and to the network capacity. Additionally, we achieve big savings in data transmission by avoiding altogether texture coordinates, which are generated automatically thanks to an unwrapping system agreed upon by both encoder and decoder

Efficient multi-bounce lightmap creation using GPU forward mapping

Computer graphics can nowadays produce images in realtime that are hard to distinguish from photos of a real scene. One of the most important aspects to achieve this is the interaction of light with materials in the virtual scene. The lighting computation can be separated in two different parts. The first part is concerned with the direct illumination that is applied to all surfaces lit by a light source; algorithms related to this have been greatly improved over the last decades and together with the improvements of the graphics hardware can now produce realistic effects. The second aspect is about the indirect illumination which describes the multiple reflections of light from each surface. In reality, light that hits a surface is never fully absorbed, but instead reflected back into the scene. And even this reflected light is then reflected again and again until its energy is depleted. These multiple reflections make indirect illumination very computationally expensive. The first problem regarding indirect illumination is therefore, how it can be simplified to compute it faster. Another question concerning indirect illumination is, where to compute it. It can either be computed in the fixed image that is created when rendering the scene or it can be stored in a light map. The drawback of the first approach is, that the results need to be recomputed for every frame in which the camera changed. The second approach, on the other hand, is already used for a long time. Once a static scene has been set up, the lighting situation is computed regardless of the time it takes and the result is then stored into a light map. This is a texture atlas for the scene in which each surface point in the virtual scene has exactly one surface point in the 2D texture atlas. When displaying the scene with this approach, the indirect illumination does not need to be recomputed, but is simply sampled from the light map. The main contribution of this thesis is the development of a technique that computes the indirect illumination solution for a scene at interactive rates and stores the result into a light atlas for visualizing it. To achieve this, we overcome two main obstacles. First, we need to be able to quickly project data from any given camera configuration into the parts of the texture that are currently used for visualizing the 3D scene. Since our approach for computing and storing indirect illumination requires a huge amount of these projections, it needs to be as fast as possible. Therefore, we introduce a technique that does this projection entirely on the graphics card with a single draw call. Second, the reflections of light into the scene need to be computed quickly. Therefore, we separate the computation into two steps, one that quickly approximates the spreading of the light into the scene and a second one that computes the visually smooth final result using the aforementioned projection technique. The final technique computes the indirect illumination at interactive rates even for big scenes. It is furthermore very flexible to let the user choose between high quality results or fast computations. This allows the method to be used for quickly editing the lighting situation with high speed previews and then computing the final result in perfect quality at still interactive rates. The technique introduced for projecting data into the texture atlas is in itself highly flexible and also allows for fast painting onto objects and projecting data onto it, considering all perspective distortions and self-occlusions

Space Carving multi-view video plus depth sequences for representation and transmission of 3DTV and FTV contents

La vidéo 3D a suscité un intérêt croissant durant ces dernières années. Grâce au développement récent des écrans stéréoscopiques et auto-stéréoscopiques, la vidéo 3D fournit une sensation réaliste de profondeur à l'utilisateur et une navigation virtuelle autour de la scène observée. Cependant de nombreux défis techniques existent encore. Ces défis peuvent être liés à l'acquisition de la scène et à sa représentation d'une part ou à la transmission des données d'autre part. Dans le contexte de la représentation de scènes naturelles, de nombreux efforts ont été fournis afin de surmonter ces difficultés. Les méthodes proposées dans la littérature peuvent être basées image, géométrie ou faire appel à des représentations combinant image et géométrie. L'approche adoptée dans cette thèse consiste en une méthode hybride s'appuyant sur l'utilisation des séquences multi-vues plus profondeur MVD (Multi-view Video plus Depth) afin de conserver le photo-réalisme de la scène observée, combinée avec un modèle géométrique, à base de maillage triangulaire, renforçant ainsi la compacité de la représentation. Nous supposons que les cartes de profondeur des données MVD fournies sont fiables et que les caméras utilisées durant l'acquisition sont calibrées, les paramètres caméras sont donc connus, mais les images correspondantes ne sont pas nécessairement rectifiées. Nous considérerons ainsi le cas général où les caméras peuvent être parallèles ou convergentes. Les contributions de cette thèse sont les suivantes. D'abord, un schéma volumétrique dédié à la fusion des cartes de profondeur en une surface maillée est proposé. Ensuite, un nouveau schéma de plaquage de texture multi-vues est proposé. Finalement, nous abordons à l'issue ce ces deux étapes de modélisation, la transmission proprement dite et comparons les performances de notre schéma de modélisation avec un schéma basé sur le standard MPEG-MVC, état de l'art dans la compression de vidéos multi-vues.3D videos have witnessed a growing interest in the last few years. Due to the recent development ofstereoscopic and auto-stereoscopic displays, 3D videos provide a realistic depth perception to the user and allows a virtual navigation around the scene. Nevertheless, several technical challenges are still remaining. Such challenges are either related to scene acquisition and representation on the one hand or to data transmission on the other hand. In the context of natural scene representation, research activities have been strengthened worldwide in order to handle these issues. The proposed methods for scene representation can be image-based, geometry based or methods combining both image and geometry. In this thesis, we take advantage of image based representations, thanks to the use of Multi-view Video plus Depth representation, in order to preserve the photorealism of the observed scene, and geometric based representations in order to enforce the compactness ofthe proposed scene representation. We assume the provided depth maps to be reliable.Besides, the considered cameras are calibrated so that the cameras parameters are known but thecorresponding images are not necessarily rectified. We consider, therefore, the general framework where cameras can be either convergent or parallel. The contributions of this thesis are the following. First, a new volumetric framework is proposed in order to mergethe input depth maps into a single and compact surface mesh. Second, a new algorithm for multi-texturing the surface mesh is proposed. Finally, we address the transmission issue and compare the performance of the proposed modeling scheme with the current standard MPEG-MVC, that is the state of the art of multi-view video compression.RENNES-INSA (352382210) / SudocSudocFranceF

Variable Resolution & Dimensional Mapping For 3d Model Optimization

Three-dimensional computer models, especially geospatial architectural data sets, can be visualized in the same way humans experience the world, providing a realistic, interactive experience. Scene familiarization, architectural analysis, scientific visualization, and many other applications would benefit from finely detailed, high resolution, 3D models. Automated methods to construct these 3D models traditionally has produced data sets that are often low fidelity or inaccurate; otherwise, they are initially highly detailed, but are very labor and time intensive to construct. Such data sets are often not practical for common real-time usage and are not easily updated. This thesis proposes Variable Resolution & Dimensional Mapping (VRDM), a methodology that has been developed to address some of the limitations of existing approaches to model construction from images. Key components of VRDM are texture palettes, which enable variable and ultra-high resolution images to be easily composited; texture features, which allow image features to integrated as image or geometry, and have the ability to modify the geometric model structure to add detail. These components support a primary VRDM objective of facilitating model refinement with additional data. This can be done until the desired fidelity is achieved as practical limits of infinite detail are approached. Texture Levels, the third component, enable real-time interaction with a very detailed model, along with the flexibility of having alternate pixel data for a given area of the model and this is achieved through extra dimensions. Together these techniques have been used to construct models that can contain GBs of imagery data

Appearance Preserving Rendering of Out-of-Core Polygon and NURBS Models

In Computer Aided Design (CAD) trimmed NURBS surfaces are widely used due to their flexibility. For rendering and simulation however, piecewise linear representations of these objects are required. A relatively new field in CAD is the analysis of long-term strain tests. After such a test the object is scanned with a 3d laser scanner for further processing on a PC. In all these areas of CAD the number of primitives as well as their complexity has grown constantly in the recent years. This growth is exceeding the increase of processor speed and memory size by far and posing the need for fast out-of-core algorithms. This thesis describes a processing pipeline from the input data in the form of triangular or trimmed NURBS models until the interactive rendering of these models at high visual quality. After discussing the motivation for this work and introducing basic concepts on complex polygon and NURBS models, the second part of this thesis starts with a review of existing simplification and tessellation algorithms. Additionally, an improved stitching algorithm to generate a consistent model after tessellation of a trimmed NURBS model is presented. Since surfaces need to be modified interactively during the design phase, a novel trimmed NURBS rendering algorithm is presented. This algorithm removes the bottleneck of generating and transmitting a new tessellation to the graphics card after each modification of a surface by evaluating and trimming the surface on the GPU. To achieve high visual quality, the appearance of a surface can be preserved using texture mapping. Therefore, a texture mapping algorithm for trimmed NURBS surfaces is presented. To reduce the memory requirements for the textures, the algorithm is modified to generate compressed normal maps to preserve the shading of the original surface. Since texturing is only possible, when a parametric mapping of the surface - requiring additional memory - is available, a new simplification and tessellation error measure is introduced that preserves the appearance of the original surface by controlling the deviation of normal vectors. The preservation of normals and possibly other surface attributes allows interactive visualization for quality control applications (e.g. isophotes and reflection lines). In the last part out-of-core techniques for processing and rendering of gigabyte-sized polygonal and trimmed NURBS models are presented. Then the modifications necessary to support streaming of simplified geometry from a central server are discussed and finally and LOD selection algorithm to support interactive rendering of hard and soft shadows is described

Enhancing detailed haptic relief for real-time interaction

The present document exposes a different approach for haptic rendering, defined as the simulation of force interactions to reproduce the sensation of surface relief in dense models. Current research shows open issues in timely haptic interaction involving large meshes, with several problems affecting performance and fidelity, and without a dominant technique to treat these issues properly. Relying in pure geometric collisions when rendering highly dense mesh models (hundreds of thousands of triangles) sensibly degrades haptic rates due to the sheer number of collisions that must be tracked between the mesh's faces and a haptic probe. Several bottlenecks were identified in order to enhance haptic performance: software architecture and data structures, collision detection, and accurate rendering of surface relief. To account for overall software architecture and data structures, it was derived a complete component framework for transforming standalone VR applications into full-fledged multi-threaded Collaborative Virtual Reality Environments (CVREs), after characterizing existing implementations into a feature-rich superset. Enhancements include: a scalable arbitrated peer-to-peer topology for scene sharing; multi-threaded components for graphics rendering, user interaction and network communications; a collaborative user interface model for session handling; and interchangeable user roles with multi-camera perspectives, avatar awareness and shared annotations. We validate the framework by converting the existing ALICE VR Navigator into a complete CVRE, showing good performance in collaborative manipulation of complex models. To specifically address collision detection computation, we derive a conformal algebra treatment for collisions among points, segments, areas, and volumes, based on collision detection in conformal R{4,1} (5D) space, and implemented in GPU for faster parallel queries. Results show orders of magnitude time reductions in collisions computations, allowing interactive rates. Finally, the main core of the research is the haptic rendering of surface mesostructure in large meshes. Initially, a method for surface haptic rendering was proposed, using image-based Hybrid Rugosity Mesostructures (HRMs) of per-face heightfield displacements and normalmaps layered on top of a simpler mesh, adding greater surface detail than actually present. Haptic perception is achieved modulating the haptic probe's force response using the HRM coat. A usability testbed framework was built to measure experimental performance with a common set tests, meshes and HRMs. Trial results show the goodness of the proposed technique, rendering accurate 3D surface detail at high sampling rates. This local per-face method is extended into a fast global approach for haptic rendering, building a mesostructure-based atlas of depth/normal textures (HyRMA), computed out of surface differences of the same mesh object at two different resolutions: original and simplified. For each triangle in the simplified mesh, an irregular prism is considered defined by the triangle's vertices and their normals. This prism completely covers the original mesh relief over the triangle. Depth distances and surfaces normals within each prism are warped from object volume space to orthogonal tangent space, by means of a novel and fast method for computing barycentric coordinates at the prism, and storing normals and relief in a sorted atlas. Haptic rendering is effected by colliding the probe against the atlas, and effecting a modulated force response at the haptic probe. The method is validated numerically, statistically and perceptually in user testing controlled trials, achieving accurate haptic sensation of large meshes' fine features at interactive rendering rates, with some minute loss of mesostructure detail.En aquesta tesi es presenta un novedós enfocament per a la percepció hàptica del relleu de models virtuals complexes mitjançant la simulació de les forces d'interacció entre la superfície i un element de contacte. La proposta contribueix a l'estat de l'art de la recerca en aquesta àrea incrementant l'eficiència i la fidelitat de la interacció hàptica amb grans malles de triangles. La detecció de col·lisions amb malles denses (centenars de milers de triangles) limita la velocitat de resposta hàptica degut al gran nombre d'avaluacions d'intersecció cara-dispositiu hàptic que s'han de realitzar. Es van identificar diferents alternatives per a incrementar el rendiment hàptic: arquitectures de software i estructures de dades específiques, algorismes de detecció de col·lisions i reproducció hàptica de relleu superficial. En aquesta tesi es presenten contribucions en alguns d'aquests aspectes. S'ha proposat una estructura completa de components per a transformar aplicacions de Realitat Virtual en Ambients Col·laboratius de Realitat Virtual (CRVEs) multithread en xarxa. L'arquitectura proposada inclou: una topologia escalable punt a punt per a compartir escenes; components multithread per a visualització gràfica, interacció amb usuaris i comunicació en xarxa; un model d'interfície d'usuari col·laboratiu per a la gestió de sessions; i rols intercanviables de l'usuari amb perspectives de múltiples càmeres, presència d'avatars i anotacions compartides. L'estructura s'ha validat convertint el navegador ALICE en un CVRE completament funcional, mostrant un bon rendiment en la manipulació col·laborativa de models complexes. Per a incrementar l'eficiència del càlcul de col·lisions, s'ha proposat un algorisme que treballa en un espai conforme R{4,1} (5D) que permet detectar col·lisions entre punts, segments, triangles i volums. Aquest algorisme s'ha implementat en GPU per obtenir una execució paral·lela més ràpida. Els resultats mostren reduccions en el temps de càlcul de col·lisions permetent interactivitat. Per a la percepció hàptica de malles complexes que modelen objectes rugosos, s'han proposat diferents algorismes i estructures de dades. Les denominades Mesoestructures Híbrides de Rugositat (HRM) permeten substituir els detalls geomètrics d'una cara (rugositats) per dues textures: de normals i d'alçades. La percepció hàptica s'aconsegueix modulant la força de resposta entre el dispositiu hàptic i la HRM. Els tests per avaluar experimentalment l'eficiència del càlcul de col·lisions i la percepció hàptica utilitzant HRM respecte a modelar les rugositats amb geometria, van mostrar que la tècnica proposada va ser encertada, permetent percebre detalls 3D correctes a altes tases de mostreig. El mètode es va estendre per a representar rugositats d'objectes. Es proposa substituir l'objecte per un model simplificat i un atles de mesoestructures en el que s'usen textures de normals i de relleus (HyRMA). Aquest atles s'obté a partir de la diferència en el detall de la superfície entre dos malles del mateix objecte: l'original i la simplificada. A partir d'un triangle de la malla simplificada es construeix un prisma, definit pels vèrtexs del triangle i les seves normals, que engloba el relleu de la malla original sobre el triangle. Les alçades i normals dins del prisma es transformen des de l'espai de volum a l'espai ortogonal tangent, amb mètode novedós i eficient que calcula les coordenades baricèntriques relatives al prisma, per a guardar el mapa de textures transformat en un atles ordenat. La percepció hàptica s'assoleix detectant les col·lisions entre el dispositiu hàptic i l'atles, i modulant la força de resposta d'acord al resultat de la col·lisió. El mètode s'ha validat numèricament, estadística i perceptual en tests amb usuaris, aconseguint una correcta i interactiva sensació tàctil dels objectes simulats mitjançant la mesoestructura de les mallesEn esta tesis se presenta un enfoque novedoso para la percepción háptica del relieve de modelos virtuales complejos mediante la simulación de las fuerzas de interacción entre la superficie y un elemento de contacto. La propuesta contribuye al estado del arte de investigación en este área incrementando la eficiencia y fidelidad de interacción háptica con grandes mallas de triángulos. La detección de colisiones con mallas geométricas densas (cientos de miles de triángulos) limita la velocidad de respuesta háptica debido al elevado número de evaluaciones de intersección cara-dispositivo háptico que deben realizarse. Se identificaron diferentes alternativas para incrementar el rendimiento háptico: arquitecturas de software y estructuras de datos específicas, algoritmos de detección de colisiones y reproducción háptica de relieve superficial. En esta tesis se presentan contribuciones en algunos de estos aspectos. Se ha propuesto una estructura completa de componentes para transformar aplicaciones aisladas de Realidad Virtual en Ambientes Colaborativos de Realidad Virtual (CRVEs) multithread en red. La arquitectura propuesta incluye: una topología escalable punto a punto para compartir escenas; componentes multithread para visualización gráfica, interacción con usuarios y comunicación en red; un modelo de interfaz de usuario colaborativo para la gestión de sesiones; y roles intercambiables del usuario con perspectivas de múltiples cámaras, presencia de avatares y anotaciones compartidas. La estructura se ha validado convirtiendo el navegador ALICE en un CVRE completamente funcional, mostrando un buen rendimiento en la manipulación colaborativa de modelos complejos. Para incrementar la eficiencia del cálculo de colisiones, se ha propuesto un algoritmo que trabaja en un espacio conforme R4,1 (5D) que permite detectar colisiones entre puntos, segmentos, triángulos y volúmenes. Este algoritmo se ha implementado en GPU a efectos de obtener una ejecución paralelamás rápida. Los resultadosmuestran reducciones en el tiempo de cálculo de colisiones permitiendo respuesta interactiva. Para la percepción háptica de mallas complejas que modelan objetos rugosos, se han propuesto diferentes algoritmos y estructuras de datos. Las denominadasMesoestructuras Híbridas de Rugosidad (HRM) permiten substituir los detalles geométricos de una cara (rugosidades) por una textura de normales y otra de alturas. La percepción háptica se consigue modulando la fuerza de respuesta entre el dispositivo háptico y la HRM. Los tests realizados para evaluar experimentalmente la eficiencia del cálculo de colisiones y la percepción háptica utilizando HRM respecto a modelar las rugosidades con geometría, mostraron que la técnica propuesta fue acertada, permitiendo percibir detalles 3D correctos a altas tasas de muestreo. Este método anterior es extendido a un procedimiento global para representar rugosidades de objetos. Para hacerlo se propone sustituir el objeto por un modelo simplificado y un atlas de mesostructuras usando texturas de normales y relieves (HyRMA). Este atlas se obtiene de la diferencia en detalle de superficie entre dos mallas del mismo objeto: la original y la simplificada. A partir de un triángulo de la malla simplificada se construye un prisma definido por los vértices del triángulo a lo largo de sus normales, que engloba completamente el relieve de la malla original sobre este triángulo. Las alturas y normales dentro de cada prisma se transforman del espacio de volumen al espacio ortoganal tangente, usando un método novedoso y eficiente que calcula las coordenadas baricéntricas relativas a cada prisma para guardar el mapa de texturas transformado en un atlas ordenado. La percepción háptica se consigue detectando directamente las colisiones entre el dispositivo háptico y el atlas, y modulando la fuerza de respuesta de acuerdo al resultado de la colisión. El procedmiento se ha validado numérica, estadística y perceptualmente en ensayos con usuarios, consiguiendo a tasas interactivas la correcta sensación táctil de los objetos simulados mediante la mesoestructura de las mallas, con alguna pérdida muy puntual de detall