The Iray Light Transport Simulation and Rendering System

While ray tracing has become increasingly common and path tracing is well understood by now, a major challenge lies in crafting an easy-to-use and efficient system implementing these technologies. Following a purely physically-based paradigm while still allowing for artistic workflows, the Iray light transport simulation and rendering system allows for rendering complex scenes by the push of a button and thus makes accurate light transport simulation widely available. In this document we discuss the challenges and implementation choices that follow from our primary design decisions, demonstrating that such a rendering system can be made a practical, scalable, and efficient real-world application that has been adopted by various companies across many fields and is in use by many industry professionals today

Efficient Many-Light Rendering of Scenes with Participating Media

We present several approaches based on virtual lights that aim at capturing the light transport without compromising quality, and while preserving the elegance and efficiency of many-light rendering. By reformulating the integration scheme, we obtain two numerically efficient techniques; one tailored specifically for interactive, high-quality lighting on surfaces, and one for handling scenes with participating media

Artistic Path Space Editing of Physically Based Light Transport

Die Erzeugung realistischer Bilder ist ein wichtiges Ziel der Computergrafik, mit Anwendungen u.a. in der Spielfilmindustrie, Architektur und Medizin. Die physikalisch basierte Bildsynthese, welche in letzter Zeit anwendungsübergreifend weiten Anklang findet, bedient sich der numerischen Simulation des Lichttransports entlang durch die geometrische Optik vorgegebener Ausbreitungspfade; ein Modell, welches für übliche Szenen ausreicht, Photorealismus zu erzielen. Insgesamt gesehen ist heute das computergestützte Verfassen von Bildern und Animationen mit wohlgestalteter und theoretisch fundierter Schattierung stark vereinfacht. Allerdings ist bei der praktischen Umsetzung auch die Rücksichtnahme auf Details wie die Struktur des Ausgabegeräts wichtig und z.B. das Teilproblem der effizienten physikalisch basierten Bildsynthese in partizipierenden Medien ist noch weit davon entfernt, als gelöst zu gelten. Weiterhin ist die Bildsynthese als Teil eines weiteren Kontextes zu sehen: der effektiven Kommunikation von Ideen und Informationen. Seien es nun Form und Funktion eines Gebäudes, die medizinische Visualisierung einer Computertomografie oder aber die Stimmung einer Filmsequenz -- Botschaften in Form digitaler Bilder sind heutzutage omnipräsent. Leider hat die Verbreitung der -- auf Simulation ausgelegten -- Methodik der physikalisch basierten Bildsynthese generell zu einem Verlust intuitiver, feingestalteter und lokaler künstlerischer Kontrolle des finalen Bildinhalts geführt, welche in vorherigen, weniger strikten Paradigmen vorhanden war. Die Beiträge dieser Dissertation decken unterschiedliche Aspekte der Bildsynthese ab. Dies sind zunächst einmal die grundlegende Subpixel-Bildsynthese sowie effiziente Bildsyntheseverfahren für partizipierende Medien. Im Mittelpunkt der Arbeit stehen jedoch Ansätze zum effektiven visuellen Verständnis der Lichtausbreitung, die eine lokale künstlerische Einflussnahme ermöglichen und gleichzeitig auf globaler Ebene konsistente und glaubwürdige Ergebnisse erzielen. Hierbei ist die Kernidee, Visualisierung und Bearbeitung des Lichts direkt im alle möglichen Lichtpfade einschließenden "Pfadraum" durchzuführen. Dies steht im Gegensatz zu Verfahren nach Stand der Forschung, die entweder im Bildraum arbeiten oder auf bestimmte, isolierte Beleuchtungseffekte wie perfekte Spiegelungen, Schatten oder Kaustiken zugeschnitten sind. Die Erprobung der vorgestellten Verfahren hat gezeigt, dass mit ihnen real existierende Probleme der Bilderzeugung für Filmproduktionen gelöst werden können

Master of Science

thesisVirtual point lights (VPLs) provide an effective solution to global illumination computation by converting the indirect illumination into direct illumination from many virtual light sources. This approach results in a less noisy image compare to Monte Carlo methods. In addition, the number of VPLs to generate can be specified in advance; therefore, it can be adjusted depending on the scene, desired quality, time budget, and the available computational power. In this thesis, we investigate a new technique that carefully places VPLs for providing improved rendering quality for computing global illumination using VPLs. Our method consists of three different passes. In the first pass, we randomly generate a large number of VPLs in the scene starting from the camera to place them in positions that can contribute to the final rendered image. Then, we remove a considerable number of these VPLs using a Poisson disk sample elimination method to get a subset of VPLs that are uniformly distributed over the part of the scene that is indirectly visible to the camera. The second pass is to estimate the radiant intensity of these VPLs by performing light tracing starting from the original light sources in the scene and scatter the radiance of light rays at a hit-point to the VPLs close to that point. The final pass is rendering the scene, which consists of shading all points in the scene visible to the camera using the original light sources and VPLs

Efficient From-Point Visibility for Global Illumination in Virtual Scenes with Participating Media

Sichtbarkeitsbestimmung ist einer der fundamentalen Bausteine fotorealistischer Bildsynthese. Da die Berechnung der Sichtbarkeit allerdings äußerst kostspielig zu berechnen ist, wird nahezu die gesamte Berechnungszeit darauf verwendet. In dieser Arbeit stellen wir neue Methoden zur Speicherung, Berechnung und Approximation von Sichtbarkeit in Szenen mit streuenden Medien vor, die die Berechnung erheblich beschleunigen, dabei trotzdem qualitativ hochwertige und artefaktfreie Ergebnisse liefern

Real-Time Volumetric Shadows using 1D Min-Max Mipmaps

Light scattering in a participating medium is responsible for several important effects we see in the natural world. In the presence of occluders, computing single scattering requires integrating the illumination scattered towards the eye along the camera ray, modulated by the visibility towards the light at each point. Unfortunately, incorporating volumetric shadows into this integral, while maintaining real-time performance, remains challenging. In this paper we present a new real-time algorithm for computing volumetric shadows in single-scattering media on the GPU. This computation requires evaluating the scattering integral over the intersections of camera rays with the shadow map, expressed as a 2D height field. We observe that by applying epipolar rectification to the shadow map, each camera ray only travels through a single row of the shadow map (an epipolar slice), which allows us to find the visible segments by considering only 1D height fields. At the core of our algorithm is the use of an acceleration structure (a 1D minmax mipmap) which allows us to quickly find the lit segments for all pixels in an epipolar slice in parallel. The simplicity of this data structure and its traversal allows for efficient implementation using only pixel shaders on the GPU

GPU-Based Global Illumination Using Lightcuts

Global Illumination aims to generate high quality images. But due to its highrequirements, it is usually quite slow. Research documented in this thesis wasintended to offer a hardware and software combined acceleration solution toglobal illumination. The GPU (using CUDA) was the hardware part of the wholemethod that applied parallelism to increase performance; the “Lightcuts”algorithm proposed by Walter (2005) at SIGGRAPH 2005 acted as the softwaremethod. As the results demonstrated in this thesis, this combined method offersa satisfactory performance boost effect for relatively complex scenes

Point-Based Rendering for Homogeneous Participating Media with Refractive Boundaries

International audienceIllumination effects in translucent materials are a combination of several physical phenomena: refraction at the surface, absorption and scattering inside the material. Because refraction can focus light deep inside the material, where it will be scattered, practical illumination simulation inside translucent materials is difficult. In this paper, we present an a Point-Based Global Illumination method for light transport on homogeneous translucent materials with refractive boundaries. We start by placing light samples inside the translucent material and organizing them into a spatial hierarchy. At rendering, we gather light from these samples for each camera ray. We compute separately the sample contributions for single, double and multiple scattering, and add them. We present two implementations of our algorithm: an offline version for high-quality rendering and an interactive GPU implementation. The offline version provides significant speed-ups and reduced memory footprints compared to state-of-the-art algorithms, with no visible impact on quality. The GPU version yields interactive frame rates: 30 fps when moving the viewpoint, 25 fps when editing the light position or the material parameters

Interactive global illumination on the CPU

Computing realistic physically-based global illumination in real-time remains one of the major goals in the fields of rendering and visualisation; one that has not yet been achieved due to its inherent computational complexity. This thesis focuses on CPU-based interactive global illumination approaches with an aim to develop generalisable hardware-agnostic algorithms. Interactive ray tracing is reliant on spatial and cache coherency to achieve interactive rates which conflicts with needs of global illumination solutions which require a large number of incoherent secondary rays to be computed. Methods that reduce the total number of rays that need to be processed, such as Selective rendering, were investigated to determine how best they can be utilised. The impact that selective rendering has on interactive ray tracing was analysed and quantified and two novel global illumination algorithms were developed, with the structured methodology used presented as a framework. Adaptive Inter- leaved Sampling, is a generalisable approach that combines interleaved sampling with an adaptive approach, which uses efficient component-specific adaptive guidance methods to drive the computation. Results of up to 11 frames per second were demonstrated for multiple components including participating media. Temporal Instant Caching, is a caching scheme for accelerating the computation of diffuse interreflections to interactive rates. This approach achieved frame rates exceeding 9 frames per second for the majority of scenes. Validation of the results for both approaches showed little perceptual difference when comparing against a gold-standard path-traced image. Further research into caching led to the development of a new wait-free data access control mechanism for sharing the irradiance cache among multiple rendering threads on a shared memory parallel system. By not serialising accesses to the shared data structure the irradiance values were shared among all the threads without any overhead or contention, when reading and writing simultaneously. This new approach achieved efficiencies between 77% and 92% for 8 threads when calculating static images and animations. This work demonstrates that, due to the flexibility of the CPU, CPU-based algorithms remain a valid and competitive choice for achieving global illumination interactively, and an alternative to the generally brute-force GPU-centric algorithms

A bidirectional formulation for Walk on Spheres

Poisson’s equations and Laplace’s equations are important linear partial differential equations (PDEs)widely used in many applications. Conventional methods for solving PDEs numerically often need todiscretize the space first, making them less efficient for complex shapes. The random walk on spheresmethod (WoS) is a grid-free Monte-Carlo method for solving PDEs that does not need to discrete thespace. We draw analogies between WoS and classical rendering algorithms, and find that the WoSalgorithm is conceptually identical to forward path tracing.We show that solving the Poisson’s equation is equivalent to solving the Green’s function for everypair of points in the domain. Inspired by similar approaches in rendering, we propose a novel WoSreformulation that operates in the reverse direction. Besides this, using the corrector function enablesus to use control variates to estimate the Green’s function. Implementations of this algorithm showimprovement over classical WoS in solving Poisson’s equation with sparse sources. Our approachopens exciting avenues for future algorithms for PDE estimation which, analogous to light transport,connect WoS walks starting from sensors and sources and combine different strategies for robustsolution algorithms in all cases