Linear Efficient Antialiased Displacement and Reflectance Mapping

International audienceWe present Linear Efficient Antialiased Displacement and Reflectance (LEADR) mapping, a reflectance filtering technique for displacement mapped surfaces. Similarly to LEAN mapping, it employs two mipmapped texture maps, which store the first two moments of the displacement gradients. During rendering, the projection of this data over a pixel is used to compute a noncentered anisotropic Beckmann distribution using only simple, linear filtering operations. The distribution is then injected in a new, physically based, rough surface microfacet BRDF model, that includes masking and shadowing effects for both diffuse and specular reflection under directional, point, and environment lighting. Furthermore, our method is compatible with animation and deformation, making it extremely general and flexible. Combined with an adaptive meshing scheme, LEADR mapping provides the very first seamless and hardware-accelerated multi-resolution representation for surfaces. In order to demonstrate its effectiveness, we render highly detailed production models in real time on a commodity GPU, with quality matching supersampled ground-truth images

Enhancing Mesh Deformation Realism: Dynamic Mesostructure Detailing and Procedural Microstructure Synthesis

Propomos uma solução para gerar dados de mapas de relevo dinâmicos para simular deformações em superfícies macias, com foco na pele humana. A solução incorpora a simulação de rugas ao nível mesoestrutural e utiliza texturas procedurais para adicionar detalhes de microestrutura estáticos. Oferece flexibilidade além da pele humana, permitindo a geração de padrões que imitam deformações em outros materiais macios, como couro, durante a animação. As soluções existentes para simular rugas e pistas de deformação frequentemente dependem de hardware especializado, que é dispendioso e de difícil acesso. Além disso, depender exclusivamente de dados capturados limita a direção artística e dificulta a adaptação a mudanças. Em contraste, a solução proposta permite a síntese dinâmica de texturas que se adaptam às deformações subjacentes da malha de forma fisicamente plausível. Vários métodos foram explorados para sintetizar rugas diretamente na geometria, mas sofrem de limitações como auto-interseções e maiores requisitos de armazenamento. A intervenção manual de artistas na criação de mapas de rugas e mapas de tensão permite controle, mas pode ser limitada em deformações complexas ou onde maior realismo seja necessário. O nosso trabalho destaca o potencial dos métodos procedimentais para aprimorar a geração de padrões de deformação dinâmica, incluindo rugas, com maior controle criativo e sem depender de dados capturados. A incorporação de padrões procedimentais estáticos melhora o realismo, e a abordagem pode ser estendida além da pele para outros materiais macios.We propose a solution for generating dynamic heightmap data to simulate deformations for soft surfaces, with a focus on human skin. The solution incorporates mesostructure-level wrinkles and utilizes procedural textures to add static microstructure details. It offers flexibility beyond human skin, enabling the generation of patterns mimicking deformations in other soft materials, such as leater, during animation. Existing solutions for simulating wrinkles and deformation cues often rely on specialized hardware, which is costly and not easily accessible. Moreover, relying solely on captured data limits artistic direction and hinders adaptability to changes. In contrast, our proposed solution provides dynamic texture synthesis that adapts to underlying mesh deformations. Various methods have been explored to synthesize wrinkles directly to the geometry, but they suffer from limitations such as self-intersections and increased storage requirements. Manual intervention by artists using wrinkle maps and tension maps provides control but may be limited to the physics-based simulations. Our research presents the potential of procedural methods to enhance the generation of dynamic deformation patterns, including wrinkles, with greater creative control and without reliance on captured data. Incorporating static procedural patterns improves realism, and the approach can be extended to other soft-materials beyond skin

Photorealistic Surface Rendering with Microfacet Theory

La synthèse d'images dites photoréalistes nécessite d'évaluer numériquement la manière dont la lumière et la matière interagissent physiquement, ce qui, malgré la puissance de calcul impressionnante dont nous bénéficions aujourd'hui et qui ne cesse d'augmenter, est encore bien loin de devenir une tâche triviale pour nos ordinateurs. Ceci est dû en majeure partie à la manière dont nous représentons les objets: afin de reproduire les interactions subtiles qui mènent à la perception du détail, il est nécessaire de modéliser des quantités phénoménales de géométries. Au moment du rendu, cette complexité conduit inexorablement à de lourdes requêtes d'entrées-sorties, qui, couplées à des évaluations d'opérateurs de filtrage complexes, rendent les temps de calcul nécessaires à produire des images sans défaut totalement déraisonnables. Afin de pallier ces limitations sous les contraintes actuelles, il est nécessaire de dériver une représentation multiéchelle de la matière. Dans cette thèse, nous construisons une telle représentation pour la matière dont l'interface correspond à une surface perturbée, une configuration qui se construit généralement via des cartes d'élévations en infographie. Nous dérivons notre représentation dans le contexte de la théorie des microfacettes (conçue à l'origine pour modéliser la réflectance de surfaces rugueuses), que nous présentons d'abord, puis augmentons en deux temps. Dans un premier temps, nous rendons la théorie applicable à travers plusieurs échelles d'observation en la généralisant aux statistiques de microfacettes décentrées. Dans l'autre, nous dérivons une procédure d'inversion capable de reconstruire les statistiques de microfacettes à partir de réponses de réflexion d'un matériau arbitraire dans les configurations de rétroréflexion. Nous montrons comment cette théorie augmentée peut être exploitée afin de dériver un opérateur général et efficace de rééchantillonnage approximatif de cartes d'élévations qui (a) préserve l'anisotropie du transport de la lumière pour n'importe quelle résolution, (b) peut être appliqué en amont du rendu et stocké dans des MIP maps afin de diminuer drastiquement le nombre de requêtes d'entrées-sorties, et (c) simplifie de manière considérable les opérations de filtrage par pixel, le tout conduisant à des temps de rendu plus courts. Afin de valider et démontrer l'efficacité de notre opérateur, nous synthétisons des images photoréalistes anticrenelées et les comparons à des images de référence. De plus, nous fournissons une implantation C++ complète tout au long de la dissertation afin de faciliter la reproduction des résultats obtenus. Nous concluons avec une discussion portant sur les limitations de notre approche, ainsi que sur les verrous restant à lever afin de dériver une représentation multiéchelle de la matière encore plus générale.Photorealistic rendering involves the numeric resolution of physically accurate light/matter interactions which, despite the tremendous and continuously increasing computational power that we now have at our disposal, is nowhere from becoming a quick and simple task for our computers. This is mainly due to the way that we represent objects: in order to reproduce the subtle interactions that create detail, tremendous amounts of geometry need to be queried. Hence, at render time, this complexity leads to heavy input/output operations which, combined with numerically complex filtering operators, require unreasonable amounts of computation times to guarantee artifact-free images. In order to alleviate such issues with today's constraints, a multiscale representation for matter must be derived. In this thesis, we derive such a representation for matter whose interface can be modelled as a displaced surface, a configuration that is typically simulated with displacement texture mapping in computer graphics. Our representation is derived within the realm of microfacet theory (a framework originally designed to model reflection of rough surfaces), which we review and augment in two respects. First, we render the theory applicable across multiple scales by extending it to support noncentral microfacet statistics. Second, we derive an inversion procedure that retrieves microfacet statistics from backscattering reflection evaluations. We show how this augmented framework may be applied to derive a general and efficient (although approximate) down-sampling operator for displacement texture maps that (a) preserves the anisotropy exhibited by light transport for any resolution, (b) can be applied prior to rendering and stored into MIP texture maps to drastically reduce the number of input/output operations, and (c) considerably simplifies per-pixel filtering operations, resulting overall in shorter rendering times. In order to validate and demonstrate the effectiveness of our operator, we render antialiased photorealistic images against ground truth. In addition, we provide C++ implementations all along the dissertation to facilitate the reproduction of the presented results. We conclude with a discussion on limitations of our approach, and avenues for a more general multiscale representation for matter

Optimization techniques for computationally expensive rendering algorithms

Realistic rendering in computer graphics simulates the interactions of light and surfaces. While many accurate models for surface reflection and lighting, including solid surfaces and participating media have been described; most of them rely on intensive computation. Common practices such as adding constraints and assumptions can increase performance. However, they may compromise the quality of the resulting images or the variety of phenomena that can be accurately represented. In this thesis, we will focus on rendering methods that require high amounts of computational resources. Our intention is to consider several conceptually different approaches capable of reducing these requirements with only limited implications in the quality of the results. The first part of this work will study rendering of time-­¿varying participating media. Examples of this type of matter are smoke, optically thick gases and any material that, unlike the vacuum, scatters and absorbs the light that travels through it. We will focus on a subset of algorithms that approximate realistic illumination using images of real world scenes. Starting from the traditional ray marching algorithm, we will suggest and implement different optimizations that will allow performing the computation at interactive frame rates. This thesis will also analyze two different aspects of the generation of anti-­¿aliased images. One targeted to the rendering of screen-­¿space anti-­¿aliased images and the reduction of the artifacts generated in rasterized lines and edges. We expect to describe an implementation that, working as a post process, it is efficient enough to be added to existing rendering pipelines with reduced performance impact. A third method will take advantage of the limitations of the human visual system (HVS) to reduce the resources required to render temporally antialiased images. While film and digital cameras naturally produce motion blur, rendering pipelines need to explicitly simulate it. This process is known to be one of the most important burdens for every rendering pipeline. Motivated by this, we plan to run a series of psychophysical experiments targeted at identifying groups of motion-­¿blurred images that are perceptually equivalent. A possible outcome is the proposal of criteria that may lead to reductions of the rendering budgets

Filtering Non-Linear Transfer Functions on Surfaces

International audienceApplying non-linear transfer functions and look-up tables to procedural functions (such as noise), surface attributes, or even surface geometry are common strategies used to enhance visual detail. Their simplicity and ability to mimic a wide range of realistic appearances have led to their adoption in many rendering problems. As with any textured or geometric detail, proper filtering is needed to reduce aliasing when viewed across a range of distances, but accurate and efficient transfer function filtering remains an open problem for several reasons: transfer functions are complex and non-linear, especially when mapped through procedural noise and/or geometry-dependent functions, and the effects of perspective and masking further complicate the filtering over a pixel's footprint. We accurately solve this problem by computing and sampling from specialized filtering distributions on the fly, yielding very fast performance. We investigate the case where the transfer function to filter is a color map applied to (macroscale) surface textures (like noise), as well as color maps applied according to (microscale) geometric details. We introduce a novel representation of a (potentially modulated) color map's distribution over pixel footprints using Gaussian statistics and, in the more complex case of high-resolution color mapped microsurface details, our filtering is view- and light-dependent, and capable of correctly handling masking and occlusion effects. Our approach can be generalized to filter other physical-based rendering quantities. We propose an application to shading with irradiance environment maps over large terrains. Our framework is also compatible with the case of transfer functions used to warp surface geometry, as long as the transformations can be represented with Gaussian statistics, leading to proper view- and light-dependent filtering results. Our results match ground truth and our solution is well suited to real-time applications, requires only a few lines of shader code (provided in supplemental material), is high performance, and has a negligible memory footprint

Semi-transparent textures based on opaque and transparent texels augmented with a thickness

Le rendu en temps réel repose sur des compromis entre la performance et le réalisme. Un de ces compromis est de représenter des matériaux plus minces tels que les tissus comme étant infiniment minces pour économiser mémoire et temps de rendu. Par contre, cette perte de dimension prive la surface de propriétés essentielles à certains effets visuels. Dans ce mémoire, nous présentons une méthode pour simuler les effets de l’épaisseur sur des surfaces semi-transparentes en utilisant des textures composées de texels opaques et transparents. Nous analysons les trous formés par les texels transparents et nous conservons de l’information sur les contours des trous dans une structure hiérarchique compatible avec la méthode de filtrage de textures par MIP map. Nous dérivons des équations représentant la proportion de lumière passant dans un trou avec des murs intérieurs en fonction de l’angle incident des rayons de lumière. Nous combinons ces équations avec l’information conservée pour calculer un terme de transparence à différents niveaux de détail en temps réel.Real-time rendering is built upon compromises between performance and realism. One such compromise is to represent thinner materials like textile as infinitely thin in order to save on memory and rendering time. However, this loss of dimension robs the surface of properties key to some visual effects. In this thesis, we present a method to simulate the effects of thickness on semi-transparent surfaces using textures consisting of opaque and transparent texels. We analyze holes formed by transparent texels and store information about the contours of the holes in a hierarchical structure compatible with the filtering method of MIP mapping. We derive equations representing the proportion of light passing through a hole as a function of the incident angle of light. The proportions of texel top, texel side wall, and hole are computed accurately. We combine these equations with the information stored to compute a transparency term at different levels of detail in real time

Imposters for particle-based datasets

Many particle-based datasets produced by molecular dynamics simulations consist of millions of particles. Current visualization techniques are incapable of representing those large-scale datasets consistently across all scales. They either produce overlysmooth representation or are prone to aliasing due to under-sampling. This work introduces a technique that captures the micro-scale surface features accurately and is able to represent the complex local illumination behavior of hundreds of particles in a single pixel-footprint. This scale-consistent technique allows for an overview that is resistant to aliasing and true to the micro-scale surface. This technique produces visualization of shock waves that could not be seen before without dedicated visualization methods. It can be applied to any opaque particle glyphs and BRDF model.Viele partikel-basierte Datensätze bestehen aus mehreren Millionen von Partikeln. Diese stammen meist aus Molekulardynamic-Simulationen. Aktuelle Visualisierungstechniken sind nicht in der Lage Datensätze dieser Größe konsistent über alle Skalen hinweg zu repräsentieren. Sie produzieren entweder stark vereinfachte Darstellungen oder sind anfällig für Aliasing, aufgrund zu niedriger Abtastraten. Diese Arbeit stellt eine neue Visualisierungstechnik vor, die die Partikeloberflächen konsistent und mit hoher Genauigkeit repräsentieren. Diese Technik basiert auf normal distribution functions und impostern. Mit ihr konnten Visualisierungen von Schockwellen in Aluminiumgittern produziert werden, die mit aktuellen Visualisierungstechniken nicht erreichbar waren