CACHED MULTI-BOUNCE SOLUTION AND RECONSTRUCTION FOR VOXEL-BASED GLOBAL ILLUMINATION

International audienceWe address the main shortcomings of the voxel-based multi-bounce global illumination method of Chatelier and Malgouyres (2006), by introducing an iterated cached method which allows increasing sampling coarse-ness at each bounce for improved efficiency, and by introducing a ray-tracing based reconstruction process for a better final image quality. The result is a competitive accurate multi-bounce global illumination method with octree voxel-based irradiance caching

Radiative Transfer Using Path Integrals for Multiple Scattering in Participating Media

The theory of light transport forms the basis by which many computer graphic renderers are implemented. The more general theory of radiative transfer has applications in the wider scientific community, including ocean and atmospheric science, medicine, and even geophysics. Accurately capturing multiple scattering physics of light transport is an issue of great concern. Multiple scattering is responsible for indirect lighting, which is desired for images where high realism is the goal. Additionally, multiple scattering is quite important for scientific applications as it is a routine phenomenon. Computationally, it is a difficult process to model. Many have developed solutions for hard surface scenes where it is assumed that light travels in straight paths, for example, scenes without participating media. However, multiple scattering for participating media is still an open question, especially in developing robust and general techniques for particularly difficult scenes. Radiative transfer can be expressed mathematically as a Feynman path integral (FPI), and we give background on how the transport kernel of the volume rendering equation can be written in terms of a FPI. To move this model into a numerical setting, we need numerical methods to solve the model. We start by focusing on the spatial and angular integrals of the volume rendering equation, and show a way to generate seed paths without regard as to if they are cast from the emitter or the sensor. Seed paths are converted into a discretized form, and we use an existing numerical method to tackle the FPI. A modified version of this technique shows how to reduce the running time from a quadratic to a linear expression. We then perform experimental analysis of the path integral calculation. The entire numerical method is put to full scale test on a distributed computing platform to calculate beam spread functions and compare the results to experimental data. The dissertation is laid out as follows. In Chapter 1, we introduce the basic concepts of light propagation for computer graphics, multiple scattering, and volume rendering. Chapter 2 offers background on the subject of FPIs and some mathematical techniques used in their numerical integration for this work. Chapter 3 is a survey of radiative transfer and multiple scattering as it is studied in computer graphics and elsewhere. Chapter 4 is a full description of the current methodology. In Section 4.1 we describe sensor and emitter geometries used for our experiments. We propose a new algorithm for creating seed paths to use in the numerical integration of the FPI in Section 4.2. Section 4.3 introduces past work in the numerical integration, formalizes it, and improves upon its running time. Section 4.4 presents some analysis of the path weighting. In Chapters 5 and 6 we run experiments using the numerical methods. The first characterizes the calculation of the path integral itself using arbitrary spatial parameters, and shows repeatability and unbiased calculation given enough samples. In the second, we calculate beam spread functions, a basic property of scattering media, and compare the calculations to experimentally acquired data. Chapter 7 presents a summary of contributions, a summary of conclusions, and future directions for the research

A graphics processing unit based method for dynamic real-time global illumination

Real-time realistic image synthesis for virtual environments has been one of the most actively researched areas in computer graphics for over a decade. Images that display physically correct illumination of an environment can be simulated by evaluating a multi-dimensional integral equation, called the rendering equation, over the surfaces of the environment. Many global illumination algorithms such as pathtracing, photon mapping and distributed ray-tracing can produce realistic images but are generally unable to cope with dynamic lighting and objects at interactive rates. It still remains one of most challenging problems to simulate physically correctly illuminated dynamic environments without a substantial preprocessing step. In this thesis we present a rendering system for dynamic environments by implementing a customized rasterizer for global illumination entirely on the graphics hardware, the Graphical Processing Unit. Our research focuses on a parameterization of discrete visibility field for efficient indirect illumination computation. In order to generate the visibility field, we propose a CUDA-based (Compute Unified Device Architecture) rasterizer which builds Layered Hit Buffers (LHB) by rasterizing polygons into multi-layered structural buffers in parallel. The LHB provides a fast visibility function for any direction at any point. We propose a cone approximation solution to resolve an aliasing problem due to limited directional discretization. We also demonstrate how to remove structure noises by adapting an interleaved sampling scheme and discontinuity buffer. We show that a gathering method amortized with a multi-level Quasi Mont Carlo method can evaluate the rendering equation in real-time. The method can realize real-time walk-through of a complex virtual environment that has a mixture of diffuse and glossy reflection, computing multiple indirect bounces on the fly. We show that our method is capable of simulating fully dynamic environments including changes of view, materials, lighting and objects at interactive rates on commodity level graphics hardware

Rendering Caustics on Non-Lambertian Surfaces

This paper presents a new technique for rendering caustics on non-Lambertian surfaces. The method is based on an extension of the photon map which removes previous restrictions limiting the usage to Lambertian surfaces. We add information about the incoming direction to the photons and this allows us to combine the photon map with arbitrary reflectance functions. Furthermore we introduce balancing of the photon map which not only reduces the memory requirements but also significantly reduces the rendering time. We have used the method to render caustics on surfaces with reflectance functions varying from Lambertian to glossy specular. Keywords: Caustics, Photon Map, Ray Tracing, Rendering. 1 Introduction Caustics provides some of the most spectacular patterns of light in nature. Caustics are formed when light reflected from or transmitted through a specular surfaces strikes a diffuse surface. An example is the caustic formed as light shines through a glass of wine onto a table. In ..

Daylight simulation with photon maps

Physically based image synthesis remains one of the most demanding tasks in the computer graphics field, whose applications have evolved along with the techniques in recent years, particularly with the decline in cost of powerful computing hardware. Physically based rendering is essentially a niche since it goes beyond the photorealistic look required by mainstream applications with the goal of computing actual lighting levels in physical quantities within a complex 3D scene. Unlike mainstream applications which merely demand visually convincing images and short rendering times, physically based rendering emphasises accuracy at the cost of increased computational overhead. Among the more specialised applications for physically based rendering is lighting simulation, particularly in conjunction with daylight. The aim of this thesis is to investigate the applicability of a novel image synthesis technique based on Monte Carlo particle transport to daylight simulation. Many materials used in daylight simulation are specifically designed to redirect light, and as such give rise to complex effects such as caustics. The photon map technique was chosen for its efficent handling of these effects. To assess its ability to produce physically correct results which can be applied to lighting simulation, a validation was carried out based on analytical case studies and on simple experimental setups. As prerequisite to validation, the photon map\u27s inherent bias/noise tradeoff is investigated. This tradeoff depends on the density estimate bandwidth used in the reconstruction of the illumination. The error analysis leads to the development of a bias compensating operator which adapts the bandwidth according to the estimated bias in the reconstructed illumination. The work presented here was developed at the Fraunhofer Institute for Solar Energy Systems (ISE) as part of the FARESYS project sponsored by the German national research foundation (DFG), and embedded into the RADIANCE rendering system.Die Erzeugung physikalisch basierter Bilder gilt heute noch als eine der rechenintensivsten Aufgaben in der Computergraphik, dessen Anwendungen sowie auch Verfahren in den letzten Jahren kontinuierlich weiterentwickelt wurden, vorangetrieben primär durch den Preisverfall leistungsstarker Hardware. Physikalisch basiertes Rendering hat sich als Nische etabliert, die über die photorealistischen Anforderungen typischer Mainstream-Applikationen hinausgeht, mit dem Ziel, Lichttechnische Größen innerhalb einer komplexen 3D Szene zu berechnen. Im Gegensatz zu Mainstream-Applikationen, die visuell überzeugend wirken sollen und kurze Rechenzeiten erforden, liegt der Schwerpunkt bei physikalisch basiertem Rendering in der Genauigkeit, auf Kosten des Rechenaufwands. Zu den eher spezialisierten Anwendungen im Gebiet des physikalisch basiertem Renderings gehört die Lichtsimulation, besonders in Bezug auf Tageslicht. Das Ziel dieser Dissertation liegt darin, die Anwendbarkeit eines neuartigen Renderingverfahrens basierend auf Monte Carlo Partikeltransport hinsichtlich Tageslichtsimulation zu untersuchen. Viele Materialien, die in der Tageslichtsimulation verwendet werden, sind speziell darauf konzipiert, Tageslicht umzulenken, und somit komplexe Phänomene wie Kaustiken hervorrufen. Das Photon-Map-Verfahren wurde aufgrund seiner effizienten Simulation solcher Effekte herangezogen. Zur Beurteilung seiner Fähigkeit, physikalisch korrekte Ergebnisse zu liefern, die in der Tageslichtsimulation anwendbar sind, wurde eine Validierung anhand analytischer Studien sowie eines einfachen experimentellen Aufbaus durchgeführt. Als Voraussetzung zur Validierung wurde der Photon Map bezüglich seiner inhärenten Wechselwirkung zwischen Rauschen und systematischem Fehler (Bias) untersucht. Diese Wechselwirkung hängt von der Bandbreite des Density Estimates ab, mit dem die Beleuchtung aus den Photonen rekonstruiert wird. Die Fehleranalyse führt zur Entwicklung eines Bias compensating Operators, der die Bandbreite dynamisch anhand des geschätzten Bias in der rekonstruierten Beleuchtung anpasst. Die hier vorgestellte Arbeit wurde am Fraunhofer Institut für Solare Energiesysteme (ISE) als teil des FARESYS Projekts entwickelt, daß von der Deutschen Forschungsgemeinschaft (DFG) finanziert wurde. Die Implementierung erfolgte im Rahmen des RADIANCE Renderingsystems

Rendering Caustics on Non-Lambertian Surfaces

This paper presents a new technique for rendering caustics on non-Lambertian surfaces. The method is based on an extension of the photon map which removes previous restrictions limiting the usage to Lambertian surfaces. We add information about the incoming direction to the photons and this allows us to combine the photon map with arbitrary reectance functions. Furthermore we introduce balancing of the photon map which not only reduces the memory requirements but also signi cantly reduces the rendering time. We have used the method to render caustics on surfaces with re ectance functions varying from Lambertian to glossy specular

Simulación visual de la iluminación : teoría, técnicas, análisis de casos

Descripció del recurs: 10 de desembre de 2015La simulación de la iluminación es uno de los grandes temas implicados en la creación de escenarios virtuales. Requiere asimilar diversas técnicas que derivan de principios teóricos, sin cuyo conocimiento será difícil utilizar bien estas técnicas y también se necesita una buena formación visual, la capacidad de observar, de razonar visualmente, de reflexionar sobre los causas que subyacen a los fenómenos visuales, a las apariencias de objetos y escenarios familares. La finalidad de este libro, que se publica en paralelo con otro sobre simulación visual de materiales, es abordar todos estos temas en profundidad, de un modo coherente. En su Iª parte, ofrece una visión general de los fundamentos teóricos de las técnicas de simulación visual, tanto por lo que hace a los conceptos y recursos disponibles, como a las capacidades y límitaciones de nuestro sistema visual. En su IIº parte, se desarrollan ejemplos de aplicación que faciliten su asimilación y su utilización práctica