Interactive VPL-based global illumination on the GPU using fuzzy clustering

Physically-based synthesis of high quality imagery, including global illumination light transport phenomena, results in a significant workload, which makes interactive rendering a very challenging task. We propose a VPL-based ray tracing approach that runs entirely in the GPU and achieves interactive frame rates while handling global illumination light transport phenomena. This approach is based on clustering both shading points and VPLs and computing visibility only among clusters' representatives. A new massively parallel K-means clustering algorithm, enables efficient execution in the GPU. Rendering artifacts, that could result from the piecewise constant approximation of the VPLs/shading points visibility function introduced by the clustering, are smoothed away by resorting to an innovative approach based on fuzzy clustering and weighted interpolation of the visibility function. The effectiveness of the proposed approach is experimentally verified for a collection of scenes, with frame rates larger than 3 fps and up to 25 fps being demonstrated

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

Techniques for efficient global illumination through virtual point lights

Treballs Finals de Grau d'Enginyeria Informàtica, Facultat de Matemàtiques, Universitat de Barcelona, Any: 2022, Director: Ricardo Jorge Rodrigues Sepúlveda Marques[en] Global illumination is the task that aims to add realism to the modeling of light in 3D scenes, all this encompasses a set of algorithms that make it possible. These algorithms take into account, in addition to the light coming directly from a light source (direct illumination), the light rays that come from the same source but have been through reflections on surfaces of the scene (reflective or not) ( indirect illumination). So this in computing science is a more complex term than it seems a priori, it refers not only to light sources, but to all the lighting conditions of the scene, that is, we have to take into account all the objects of the scene since each one will influence the others in one way or another with the light that it reflects, refracts or absorbs. To be more precise to calculate GI we need a description of the virtual scene which includes the position, size and orientation of the 3D geometric objects that compose the scene, the material associated with each object, the position and characteristics of the light sources which illuminate the scene, and a virtual camera that defines how a scene is seen. Once this is defined, one needs to compute/simulate how light is emitted from the light sources and bounces on the scene until it hits the image plane. The light that hits each pixel of the image will define the pixel color. To calculate all this lighting we need a very high computing capacity if we want to do it in a reasonable time, or some algorithms that optimize this calculation, and this is what we will deal with in this thesis. We will start by talking about the use of the Virtual Point Lights algorithm, also called Instant Radiosity by some authors. This algorithm is able to generate images of comparable quality to that of, for example, the Path Tracing (which is a standard algorithm in photo-realistic rendering). -We will explain how the VPLs algorithm works and how it is able to render an image in less time than Path Tracing and explain how the images are generated. Furthermore, we will also discuss the artifacts that are generated using the original virtual point lights and how to solve them. The core of this work is the acceleration of the original VPLs algorithm. To this end, we will resort to clustering techniques, which will allow us to drastically reduce the number of computations involved. In particular, we will provide details on the implementation of the K-means algorithm (a type of non-supervised learning) and its application in the context of VPLs-based image synthesis. We will show how K-means can be used to cluster the visible points from each pixel, and also to cluster the virtual light points. We provide detailed results using the four different algorithms: the original VPLs algorithm, which we have implemented from scratch; VPLs with K-means clustering of the visible points; VPLs using K-means clustering of the VPLsa; and, finally, the results when using both K-means clustering fo the visible points and of the VPLs. The results show clear improvements in image synthesis time. Finally we will present the results obtained from the perspective of the final image quality . We identify the main limitation of the methods developed, and propose improvements for future work

Realistic Image Synthesis with Light Transport

Ph.DDOCTOR OF PHILOSOPH

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

Lichttransportsimulation auf Spezialhardware

It cannot be denied that the developments in computer hardware and in computer algorithms strongly influence each other, with new instructions added to help with video processing, encryption, and in many other areas. At the same time, the current cap on single threaded performance and wide availability of multi-threaded processors has increased the focus on parallel algorithms. Both influences are extremely prominent in computer graphics, where the gaming and movie industries always strive for the best possible performance on the current, as well as future, hardware. In this thesis we examine the hardware-algorithm synergies in the context of ray tracing and Monte-Carlo algorithms. First, we focus on the very basic element of all such algorithms - the casting of rays through a scene, and propose a dedicated hardware unit to accelerate this common operation. Then, we examine existing and novel implementations of many Monte-Carlo rendering algorithms on massively parallel hardware, as full hardware utilization is essential for peak performance. Lastly, we present an algorithm for tackling complex interreflections of glossy materials, which is designed to utilize both powerful processing units present in almost all current computers: the Centeral Processing Unit (CPU) and the Graphics Processing Unit (GPU). These three pieces combined show that it is always important to look at hardware-algorithm mapping on all levels of abstraction: instruction, processor, and machine.Zweifelsohne beeinflussen sich Computerhardware und Computeralgorithmen gegenseitig in ihrer Entwicklung: Prozessoren bekommen neue Instruktionen, um zum Beispiel Videoverarbeitung, Verschlüsselung oder andere Anwendungen zu beschleunigen. Gleichzeitig verstärkt sich der Fokus auf parallele Algorithmen, bedingt durch die limitierte Leistung von für einzelne Threads und die inzwischen breite Verfügbarkeit von multi-threaded Prozessoren. Beide Einflüsse sind im Grafikbereich besonders stark , wo es z.B. für die Spiele- und Filmindustrie wichtig ist, die bestmögliche Leistung zu erreichen, sowohl auf derzeitiger und zukünftiger Hardware. In Rahmen dieser Arbeit untersuchen wir die Synergie von Hardware und Algorithmen anhand von Ray-Tracing- und Monte-Carlo-Algorithmen. Zuerst betrachten wir einen grundlegenden Hardware-Bausteins für alle diese Algorithmen, die Strahlenverfolgung in einer Szene, und präsentieren eine spezielle Hardware-Einheit zur deren Beschleunigung. Anschließend untersuchen wir existierende und neue Implementierungen verschiedener MonteCarlo-Algorithmen auf massiv-paralleler Hardware, wobei die maximale Auslastung der Hardware im Fokus steht. Abschließend stellen wir dann einen Algorithmus zur Berechnung von komplexen Beleuchtungseffekten bei glänzenden Materialien vor, der versucht, die heute fast überall vorhandene Kombination aus Hauptprozessor (CPU) und Grafikprozessor (GPU) optimal auszunutzen. Zusammen zeigen diese drei Aspekte der Arbeit, wie wichtig es ist, Hardware und Algorithmen auf allen Ebenen gleichzeitig zu betrachten: Auf den Ebenen einzelner Instruktionen, eines Prozessors bzw. eines gesamten Systems

Clustering bidireccional en iluminación global basada en puntos

La síntesis de imágenes fotorrealistas por ordenador, requiere modelar y simular de forma precisa las interacciones entre luz y materia. Para conseguir este realismo, no sólo se debe calcular la iluminación que proviene de las distintas fuentes de luz que iluminan la escena, si no que también se debe tener en cuenta la energía reflejada entre las distintas superficies, denominada iluminación global. A pesar de los grandes avances tecnológicos, la generación de este tipo de imágenes requiere de una gran cantidad de tiempo y recursos. En producciones cinematográficas este coste tiene un importante impacto debido a la complejidad de las escenas modeladas además de la necesidad de generar miles de fotogramas. Por ello, las productoras invierten millones de dólares en potentes clusters de cálculo para la generación de contenido digital de sus películas, siendo la investigación y desarrollo de nuevas técnicas un tema de gran interés. En los últimos años, han surgido técnicas capaces de calcular la iluminación global de forma aproximada. A pesar de ofrecer resultados aproximados, son lo suficientemente convincentes como para que sus errores pasen desapercibidos. Algunos de estos métodos simulan la luz reflejada por las superficies como un conjunto de luces virtuales (VPLs), calculando su contribución mediante una evaluación jerárquica de las mismas, agrupando VPLs similares como una única fuente de energía. Debido a su eficiencia, estas técnicas han sido extensamente utilizadas en multitud de producciones cinematográficas. A pesar de su eficiencia, estos métodos no escalan bien con el número de píxels a iluminar. Este hecho se agrava con las enormes resoluciones necesarias en la creación de contenido digital. La alta definición se ha convertido en un estándar y el contenido 3D se está implantando progresivamente, donde la generación de imágenes desde múltiples puntos de vista es necesaria. Sin embargo, las muestras generadas desde la cámara presentan una coherencia que puede ser explotada para aproximar la luz que reciben. En este proyecto se aborda el desarrollo de una nueva técnica para el cálculo de la iluminación global basada en VPLs, que explota las similitudes entre las muestras desde la cámara y las VPLs para reducir de forma adaptativa la cantidad de computación, mediante la evaluación jerárquica de las contribuciones de las luces sobre los puntos a iluminar. De esta manera, podemos desarrollar un algoritmo capaz de generar imágenes o grupos de imágenes de alta resolución con gran cantidad de elementos de iluminación con costes sublineales, tanto en el número de luces virtuales como en el número de píxels.

Sequential Monte Carlo Instant Radiosity

Instant Radiosity and its derivatives are interactive methods for efficiently estimating global (indirect) illumination. They represent the last indirect bounce of illumination before the camera as the composite radiance field emitted by a set of virtual point light sources (VPLs). In complex scenes, current algorithms suffer from a difficult combination of two issues: it remains a challenge to distribute VPLs in a manner that simultaneously gives a high-quality indirect illumination solution for each frame, and does so in a temporally coherent manner. We address both issues by building, and maintaining over time, an adaptive and temporally coherent distribution of VPLs in locations where they bring indirect light to the image. We introduce a novel heuristic sampling method that strives to only move as few of the VPLs between frames as possible. The result is, to the best of our knowledge, the first interactive global illumination algorithm that works in complex, highly-occluded scenes, suffers little from temporal flickering, supports moving cameras and light sources, and is output-sensitive in the sense that it places VPLs in locations that matter most to the final result

Sequential Monte Carlo Instant Radiosity

Instant Radiosity and its derivatives are interactive methods for efficiently estimating global (indirect) illumination. They represent the last indirect bounce of illumination before the camera as the composite radiance field emitted by a set of virtual point light sources (VPLs). In complex scenes, current algorithms suffer from a difficult combination of two issues: it remains a challenge to distribute VPLs in a manner that simultaneously gives a high-quality indirect illumination solution for each frame, and to do so in a temporally coherent manner. We address both issues by building, and maintaining overtime, an adaptive and temporally coherent distribution of VPLs in locations where they bring indirect light to the image. We introduce a novel heuristic sampling method that strives to only move as few of the VPLs between frames as possible. The result is, to the best of our knowledge, the first interactive global illumination algorithm that works in complex, highly-occluded scenes, suffers little from temporal flickering, supports moving cameras and light sources, and is output-sensitive in the sense that it places VPLs in locations that matter most to the final result

A Frequency Analysis and Dual Hierarchy for Efficient Rendering of Subsurface Scattering

International audienceBSSRDFs are commonly used to model subsurface light transport in highly scattering media such as skin and marble. Rendering with BSSRDFs requires an additional spatial integration, which can be significantly more expensive than surface-only rendering with BRDFs. We introduce a novel hierarchical rendering method that can mitigate this additional spatial integration cost. Our method has two key components: a novel frequency analysis of subsurface light transport, and a dual hierarchy over shading and illumination samples. Our frequency analysis predicts the spatial and angular variation of outgoing radiance due to a BSSRDF. We use this analysis to drive adaptive spatial BSSRDF integration with sparse image and illumination samples. We propose the use of a dual-tree structure that allows us to simultaneously traverse a tree of shade points (i.e., pixels) and a tree of object-space illumination samples. Our dual-tree approach generalizes existing single-tree accelerations. Both our frequency analysis and the dual-tree structure are compatible with most existing BSSRDF models, and we show that our method improves rendering times compared to the state of the art method of Jensen and Buhler