Fast photorealistic techniques to simulate global illumination in videogames and virtual environments

Per al càlcul de la il·luminació global per a la síntesi d'imatges d'escenaris virtuals s'usen mètodes físicament acurats com a radiositat o el ray-tracing. Aquests mètodes són molt potents i capaços de generar imatges de gran realisme, però són molt costosos. A aquesta tesi presenta algunes tècniques per simular i/o accelerar el càlcul de la il·luminació global. La tècnica de les obscurances es basa en la suposició que com més amagat és un punt a l'escena, més fosc s'ha de veure. Es calcula analitzant l'entorn geomètric del punt i ens dóna un valor per a la seva il·luminació indirecta, que no és físicament acurat, però sí aparentment realista.Aquesta tècnica es millora per a entorns en temps real com els videojocs. S'aplica també a entorns de ray-tracing per a la generació d'imatges realistes. En aquest context, el càlcul de seqüències de frames per a l'animació de llums i càmeres s'accelera enormement reusant informació entre frames.Les obscurances serveixen per a simular la il·luminació indirecta d'una escena. La llum directa es calcula apart i de manera independent. El desacoblament de la llum directa i la indirecta és una gran avantatge, i en treurem profit. Podem afegir fàcilment l'efecte de coloració entre objectes sense afegir temps de càlcul. Una altra avantatge és que per calcular les obscurances només hem d'analitzar un entorn limitat al voltant del punt.Per escenes virtuals difuses, la radiositat es pot precalcular i l'escena es pot navegar amb apariència realista, però si un objecte de l'escena es mou en un entorn dinàmic en temps real, com un videojoc, el recàlcul de la il·luminació global de l'escena és prohibitiu. Com les obscurances es calculen en un entorn limitat, es poden recalcular en temps real per a l'entorn de l'objecte que es mou a cada frame i encara aconseguir temps real.A més, podem fer servir les obscurances per a calcular imatges de gran qualitat, o per seqüències d'imatges per una animació, com en el ray-tracing. Això ens permet tractar materials no difusos i investigar l'ús de tècniques normalment difuses com les obscurances en entorns generals. Quan la càmera està estàtica, l'ús d'animació de llum només afecta la il·luminació directa, i si usem obscurances per a la llum indirecta, gràcies al seu desacoblament, el càlcul de sèries de frames per a una animació és molt ràpid. El següent pas és afegir animació de càmera, reusant els valors de les obscurances entre frames. Aquesta última tècnica de reús d'informació de la il·luminació del punt d'impacte entre frames la podem usar per a tècniques acurades d'il·luminació global com el path-tracing, i nosaltres estudiem com reusar aquesta informació de manera no esbiaixada. A més, estudiem diferents tècniques de mostreig per a la semi-esfera, i les obscurances es calculen amb una nova tècnica, aplicant depth peeling amb GPU.To compute global illumination solutions for rendering virtual scenes, physically accurate methods based on radiosity or ray-tracing are usually employed. These methods, though powerful and capable of generating images with high realism, are very costly. In this thesis, some techniques to simulate and/or accelerate the computation of global illumination are studied. The obscurances technique is based on the supposition that the more occluded is a point in the scene, the darker it will appear. It is computed by analyzing the geometric environment of the point and gives a value for the indirect illumination for the point that is, though not physically accurate, visually realistic. This technique is enhanced and improved in real-time environments as videogames. It is also applied to ray-tracing frameworks to generate realistic images. In this last context, sequences of frames for animation of lights and cameras are dramatically accelerated by reusing information between frames.The obscurances are computed to simulate the indirect illumination of a scene. The direct lighting is computed apart and in an independent way. The decoupling of direct and indirect lighting is a big advantage, and we will take profit from this. We can easily add color bleeding effects without adding computation time. Another advantage is that to compute the obscurances we only need to analyze a limited environment around the point. For diffuse virtual scenes, the radiosity can be precomputed and we can navigate the scene with a realistic appearance. But when a small object moves in a dynamic real-time virtual environment, as a videogame, the recomputation of the global illumination of the scene is prohibitive. Thanks to the limited reach of the obscurance computation, we can recompute the obscurances only for the limited environment of the moving object for every frame and still have real-time frame rates. Obscurances can also be used to compute high quality images, or sequences of images for an animation, in a ray-tracing-like. This allows us to deal with non-diffuse materials and to research the use of a commonly diffuse technique as obscurances in general environments. For static cameras, using light animation only affects to direct lighting, and if we use obscurances for the indirect lighting, thanks to the decoupling of direct and indirect illumination, the computation of a series of frames for the animation is very fast. The next step is to add camera animation, reusing the obscurances results between frames. Using this last technique of reusing the illumination of the hit points between frames for a true global illumination technique as path tracing, we study how we can reuse this information in an unbiased way. Besides, a study of different sampling techniques for the hemisphere is made, obscurances are computed with the depth-peeling technique and using GPU

Path manipulation strategies for rendering dynamic environments.

The current work introduces path manipulation as a tool that extends bidirectional path tracing to reuse paths in the temporal domain. Defined as an apparatus of sampling and reuse strategies, path manipulation reconstructs the subpaths that compose the light transport paths and addresses the restriction of static geometry commonly associated with Monte Carlo light transport simulations. By reconstructing and reusing subpaths, the path manipulation algorithm obviates the regeneration of the entire path collection, reduces the computational load of the original algorithm and supports scene dynamism. Bidirectional path tracing relies on local path sampling techniques to generate the paths of light in a synthetic environment. By using the information localized at path vertices, like the probability distribution, the sampling techniques construct paths progressively with distinct probability densities. Each probability density corresponds to a particular sampling technique, which accounts for specific illumination effects. Bidirectional path tracing uses multiple importance sampling to combine paths sampled with different techniques in low-variance estimators. The path sampling techniques and multiple importance sampling are the keys to the efficacy of bidirectional path tracing. However, the sampling techniques gained little attention beyond the generation and evaluation of paths. Bidirectional path tracing was designed for static scenes and thus it discards the generated paths immediately after the evaluation of their contributions. Limiting the lifespan of paths to a generation-evaluation cycle imposes a static use of paths and of sampling techniques. The path manipulation algorithm harnesses the potential of the sampling techniques to supplant the static manipulation of paths with a generation-evaluation-reuse cycle. An intra-subpath connectivity strategy was devised to reconnect the segregated chains of the subpaths invalidated by the scene alterations. Successful intra-subpath connections generate subpaths in multiple pieces by reusing subpath chains from prior frames. Subpaths are reconstructed generically, regardless of the subpath or scene dynamism type and without the need for predefined animation paths. The result is the extension of bidirectional path tracing to the temporal domain

Inverse Global Illumination using a Neural Radiometric Prior

Inverse rendering methods that account for global illumination are becoming more popular, but current methods require evaluating and automatically differentiating millions of path integrals by tracing multiple light bounces, which remains expensive and prone to noise. Instead, this paper proposes a radiometric prior as a simple alternative to building complete path integrals in a traditional differentiable path tracer, while still correctly accounting for global illumination. Inspired by the Neural Radiosity technique, we use a neural network as a radiance function, and we introduce a prior consisting of the norm of the residual of the rendering equation in the inverse rendering loss. We train our radiance network and optimize scene parameters simultaneously using a loss consisting of both a photometric term between renderings and the multi-view input images, and our radiometric prior (the residual term). This residual term enforces a physical constraint on the optimization that ensures that the radiance field accounts for global illumination. We compare our method to a vanilla differentiable path tracer, and more advanced techniques such as Path Replay Backpropagation. Despite the simplicity of our approach, we can recover scene parameters with comparable and in some cases better quality, at considerably lower computation times.Comment: Homepage: https://inverse-neural-radiosity.github.i

Efficient global illumination for dynamic scenes

The production of high quality animations which feature compelling lighting effects is computationally a very heavy task when traditional rendering approaches are used where each frame is computed separately. The fact that most of the computation must be restarted from scratch for each frame leads to unnecessary redundancy. Since temporal coherence is typically not exploited, temporal aliasing problems are also more difficult to address. Many small errors in lighting distribution cannot be perceived by human observers when they are coherent in temporal domain. However, when such a coherence is lost, the resulting animations suffer from unpleasant flickering effects. In this thesis, we propose global illumination and rendering algorithms, which are designed specifically to combat those problems. We achieve this goal by exploiting temporal coherence in the lighting distribution between the subsequent animation frames. Our strategy relies on extending into temporal domain wellknown global illumination and rendering techniques such as density estimation path tracing, photon mapping, ray tracing, and irradiance caching, which have been originally designed to handle static scenes only. Our techniques mainly focus on the computation of indirect illumination, which is the most expensive part of global illumination modelling.Die Erstellung von hochqualitativen 3D-Animationen mit anspruchsvollen Lichteffekten ist für traditionelle Renderinganwendungen, bei denen jedes Bild separat berechnet wird, sehr aufwendig. Die Tatsache jedes Bild komplett neu zu berechnen führt zu unnötiger Redundanz. Wenn temporale Koherenz vernachlässigt wird, treten unter anderem auch schwierig zu behandelnde temporale Aliasingprobleme auf. Viele kleine Fehler in der Beleuchtungsberechnung eines Bildes können normalerweise nicht wahr genommen werden. Wenn jedoch die temporale Koherenz zwischen aufeinanderfolgenden Bildern fehlt, treten störende Flimmereffekte auf. In dieser Arbeit stellen wir globale Beleuchtungsalgorithmen vor, die die oben genannten Probleme behandeln. Dies erreichen wir durch Ausnutzung von temporaler Koherenz zwischen aufeinanderfolgenden Einzelbildern einer Animation. Unsere Strategy baut auf die klassischen globalen Beleuchtungsalgorithmen wie "Path tracing", "Photon Mapping" und "Irradiance Caching" auf und erweitert diese in die temporale Domäne. Dabei beschränken sich unsereMethoden hauptsächlich auf die Berechnung indirekter Beleuchtung, welche den zeitintensivsten Teil der globalen Beleuchtungsberechnung darstellt

Efficient global illumination for dynamic scenes

The production of high quality animations which feature compelling lighting effects is computationally a very heavy task when traditional rendering approaches are used where each frame is computed separately. The fact that most of the computation must be restarted from scratch for each frame leads to unnecessary redundancy. Since temporal coherence is typically not exploited, temporal aliasing problems are also more difficult to address. Many small errors in lighting distribution cannot be perceived by human observers when they are coherent in temporal domain. However, when such a coherence is lost, the resulting animations suffer from unpleasant flickering effects. In this thesis, we propose global illumination and rendering algorithms, which are designed specifically to combat those problems. We achieve this goal by exploiting temporal coherence in the lighting distribution between the subsequent animation frames. Our strategy relies on extending into temporal domain wellknown global illumination and rendering techniques such as density estimation path tracing, photon mapping, ray tracing, and irradiance caching, which have been originally designed to handle static scenes only. Our techniques mainly focus on the computation of indirect illumination, which is the most expensive part of global illumination modelling.Die Erstellung von hochqualitativen 3D-Animationen mit anspruchsvollen Lichteffekten ist für traditionelle Renderinganwendungen, bei denen jedes Bild separat berechnet wird, sehr aufwendig. Die Tatsache jedes Bild komplett neu zu berechnen führt zu unnötiger Redundanz. Wenn temporale Koherenz vernachlässigt wird, treten unter anderem auch schwierig zu behandelnde temporale Aliasingprobleme auf. Viele kleine Fehler in der Beleuchtungsberechnung eines Bildes können normalerweise nicht wahr genommen werden. Wenn jedoch die temporale Koherenz zwischen aufeinanderfolgenden Bildern fehlt, treten störende Flimmereffekte auf. In dieser Arbeit stellen wir globale Beleuchtungsalgorithmen vor, die die oben genannten Probleme behandeln. Dies erreichen wir durch Ausnutzung von temporaler Koherenz zwischen aufeinanderfolgenden Einzelbildern einer Animation. Unsere Strategy baut auf die klassischen globalen Beleuchtungsalgorithmen wie "Path tracing", "Photon Mapping" und "Irradiance Caching" auf und erweitert diese in die temporale Domäne. Dabei beschränken sich unsereMethoden hauptsächlich auf die Berechnung indirekter Beleuchtung, welche den zeitintensivsten Teil der globalen Beleuchtungsberechnung darstellt

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

Neural probabilistic path prediction : skipping paths for acceleration

La technique de tracé de chemins est la méthode Monte Carlo la plus populaire en infographie pour résoudre le problème de l'illumination globale. Une image produite par tracé de chemins est beaucoup plus photoréaliste que les méthodes standard tel que le rendu par rasterisation et même le lancer de rayons. Mais le tracé de chemins est coûteux et converge lentement, produisant une image bruitée lorsqu'elle n'est pas convergée. De nombreuses méthodes visant à accélérer le tracé de chemins ont été développées, mais chacune présente ses propres défauts et contraintes. Dans les dernières avancées en apprentissage profond, en particulier dans le domaine des modèles génératifs conditionnels, il a été démontré que ces modèles sont capables de bien apprendre, modéliser et tirer des échantillons à partir de distributions complexes. Comme le tracé de chemins dépend également d'un tel processus sur une distribution complexe, nous examinons les similarités entre ces deux problèmes et modélisons le processus de tracé de chemins comme un processus génératif. Ce processus peut ensuite être utilisé pour construire un estimateur efficace avec un réseau neuronal afin d'accélérer le temps de rendu sans trop d'hypothèses sur la scène. Nous montrons que notre estimateur neuronal (NPPP), utilisé avec le tracé de chemins, peut améliorer les temps de rendu d'une manière considérable sans beaucoup compromettre sur la qualité du rendu. Nous montrons également que l'estimateur est très flexible et permet à un utilisateur de contrôler et de prioriser la qualité ou le temps de rendu, sans autre modification ou entraînement du réseau neuronal.Path tracing is one of the most popular Monte Carlo methods used in computer graphics to solve the problem of global illumination. A path traced image is much more photorealistic compared to standard rendering methods such as rasterization and even ray tracing. Unfortunately, path tracing is expensive to compute and slow to converge, resulting in noisy images when unconverged. Many methods aimed to accelerate path tracing have been developed, but each has its own downsides and limitiations. Recent advances in deep learning, especially with conditional generative models, have shown to be very capable at learning, modeling, and sampling from complex distributions. As path tracing is also dependent on sampling from complex distributions, we investigate the similarities between the two problems and model the path tracing process itself as a conditional generative process. It can then be used to build an efficient neural estimator that allows us to accelerate rendering time with as few assumptions as possible. We show that our neural estimator (NPPP) used along with path tracing can improve rendering time by a considerable amount without compromising much in rendering quality. The estimator is also shown to be very flexible and allows a user to control and prioritize quality or rendering time, without any further training or modifications to the neural network

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

Towards Fully Dynamic Surface Illumination in Real-Time Rendering using Acceleration Data Structures

The improvements in GPU hardware, including hardware-accelerated ray tracing, and the push for fully dynamic realistic-looking video games, has been driving more research in the use of ray tracing in real-time applications. The work described in this thesis covers multiple aspects such as optimisations, adapting existing offline methods to real-time constraints, and adding effects which were hard to simulate without the new hardware, all working towards a fully dynamic surface illumination rendering in real-time.Our first main area of research concerns photon-based techniques, commonly used to render caustics. As many photons can be required for a good coverage of the scene, an efficient approach for detecting which ones contribute to a pixel is essential. We improve that process by adapting and extending an existing acceleration data structure; if performance is paramount, we present an approximation which trades off some quality for a 2–3× improvement in rendering time. The tracing of all the photons, and especially when long paths are needed, had become the highest cost. As most paths do not change from frame to frame, we introduce a validation procedure allowing the reuse of as many as possible, even in the presence of dynamic lights and objects. Previous algorithms for associating pixels and photons do not robustly handle specular materials, so we designed an approach leveraging ray tracing hardware to allow for caustics to be visible in mirrors or behind transparent objects.Our second research focus switches from a light-based perspective to a camera-based one, to improve the picking of light sources when shading: photon-based techniques are wonderful for caustics, but not as efficient for direct lighting estimations. When a scene has thousands of lights, only a handful can be evaluated at any given pixel due to time constraints. Current selection methods in video games are fast but at the cost of introducing bias. By adapting an acceleration data structure from offline rendering that stochastically chooses a light source based on its importance, we provide unbiased direct lighting evaluation at about 30 fps. To support dynamic scenes, we organise it in a two-level system making it possible to only update the parts containing moving lights, and in a more efficient way.We worked on top of the new ray tracing hardware to handle lighting situations that previously proved too challenging, and presented optimisations relevant for future algorithms in that space. These contributions will help in reducing some artistic constraints while designing new virtual scenes for real-time applications