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

Novel illumination algorithms for off-line and real-time rendering

This thesis presents new and efficient illumination algorithms for off-line and real-time rendering. The realistic rendering of arbitrary indirect illumination is a difficult task. Assuming ray optics model of light, the rendering equation describes the propagation of light in the scene with high accuracy. However, the computation is expensive, and thus even in off-line rendering, i.e., in prerendered animations, indirect illumination is often approximated as it would otherwise constitute a bottleneck in the production pipeline. Indirect illumination can be computed using Monte Carlo integration, but when restrained to a reasonable amount of computation time, the result is often corrupted by noise. This thesis includes a method that effectively reduces the noise by applying a spatially varying filter to the noisy illumination. For real-time performance, some components of indirect illumination can be precomputed. Irradiance volume and many variations of it precompute reflections and shadowing of a static scene into a volumetric data structure. This data is then used to shade dynamic objects in real-time. The practical usage of the method is limited due to aliasing artifacts. This thesis shows that with a suitable super-sampling approach, a significant quality improvement can be obtained. Another direction is to precompute how light propagates in the scene and use the precomputed data during run-time to solve both direct and indirect illumination based on the known incident lighting. To keep the memory and precomputation costs tractable, these methods are typically restricted to infinitely distant lighting. Those that are not, require a very long precomputation time. This thesis presents an algorithm that adopts a wavelet-based hierarchical finite element method for the precomputation. A significant performance improvement over the existing techniques is obtained. When full global illumination cannot be afforded, ambient occlusion is an attractive alternative. This thesis includes two methods for real-time rendering of ambient occlusion in dynamic scenes. The first method models the shadowing of ambient light between rigid moving bodies. The second method gives a data-oriented solution for rendering approximate ambient occlusion for animated characters in real-time. Both methods achieve unprecedented efficiency.reviewe

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

Frequency Analysis and Sheared Filtering for Multidimensional Effects in Rendering

Many of the most expensive effects in rendering are those that require integrating complex multidimensional signals. Computation for a single pixel can require hundreds of samples, and standard methods do not provide a mathematically sound way to share samples between pixels with overlapping integrands. This thesis first analyzes the underlying signals for motion blur and occlusion and identifies the sparse structure of these signals in the Fourier domain. We then leverage this information to design a sheared filter that is customized to each pixel's frequency content. We finally present practical algorithms that share samples between pixels, reduce sampling requirements by an order of magnitude, and provide significant speedups for many of the most expensive computations in computer graphics

Perceptually-motivated, interactive rendering and editing of global illumination

This thesis proposes several new perceptually-motivated techniques to synthesize, edit and enhance depiction of three-dimensional virtual scenes. Finding algorithms that fit the perceptually economic middle ground between artistic depiction and full physical simulation is the challenge taken in this work. First, we will present three interactive global illumination rendering approaches that are inspired by perception to efficiently depict important light transport. Those methods have in common to compute global illumination in large and fully dynamic scenes allowing for light, geometry, and material changes at interactive or real-time rates. Further, this thesis proposes a tool to edit reflections, that allows to bend physical laws to match artistic goals by exploiting perception. Finally, this work contributes a post-processing operator that depicts high contrast scenes in the same way as artists do, by simulating it "seen'; through a dynamic virtual human eye in real-time.Diese Arbeit stellt eine Anzahl von Algorithmen zur Synthese, Bearbeitung und verbesserten Darstellung von virtuellen drei-dimensionalen Szenen vor. Die Herausforderung liegt dabei in der Suche nach Ausgewogenheit zwischen korrekter physikalischer Berechnung und der künstlerischen, durch die Gesetze der menschlichen Wahrnehmung motivierten Praxis. Zunächst werden drei Verfahren zur Bild-Synthese mit globaler Beleuchtung vorgestellt, deren Gemeinsamkeit in der effizienten Handhabung großer und dynamischer virtueller Szenen liegt, in denen sich Geometrie, Materialen und Licht frei verändern lassen. Darauffolgend wird ein Werkzeug zum Editieren von Reflektionen in virtuellen Szenen das die menschliche Wahrnehmung ausnutzt um künstlerische Vorgaben umzusetzen, vorgestellt. Die Arbeit schließt mit einem Filter am Ende der Verarbeitungskette, der den wahrgenommen Kontrast in einem Bild erhöht, indem er die Entstehung von Glanzeffekten im menschlichen Auge nachbildet

Utilising path-vertex data to improve Monte Carlo global illumination.

Efficient techniques for photo-realistic rendering are in high demand across a wide array of industries. Notable applications include visual effects for film, entertainment and virtual reality. Less direct applications such as visualisation for architecture, lighting design and product development also rely on the synthesis of realistic and physically based illumination. Such applications assert ever increasing demands on light transport algorithms, requiring the computation of photo-realistic effects while handling complex geometry, light scattering models and illumination. Techniques based on Monte Carlo integration handle such scenarios elegantly and robustly, but despite seeing decades of focused research and wide commercial support, these methods and their derivatives still exhibit undesirable side effects that are yet to be resolved. In this thesis, Monte Carlo path tracing techniques are improved upon by utilizing path vertex data and intermediate radiance contributions readily available during rendering. This permits the development of novel progressive algorithms that render low noise global illumination while striving to maintain the desirable accuracy and convergence properties of unbiased methods. The thesis starts by presenting a discussion into optical phenomenon, physically based rendering and achieving photo realistic image synthesis. This is followed by in-depth discussion of the published theoretical and practical research in this field, with a focus on stochastic methods and modem rendering methodologies. This provides insight into the issues surrounding Monte Carlo integration both in the general and rendering specific contexts, along with an appreciation for the complexities of solving global light transport. Alternative methods that aim to address these issues are discussed, providing an insight into modem rendering paradigms and their characteristics. Thus, an understanding of the key aspects is obtained, that is necessary to build up and discuss the novel research and contributions to the field developed throughout this thesis. First, a path space filtering strategy is proposed that allows the path-based space of light transport to be classified into distinct subsets. This permits the novel combination of robust path tracing and recent progressive photon mapping algorithms to handle each subset based on the characteristics of the light transport in that space. This produces a hybrid progressive rendering technique that utilises the strengths of existing state of the art Monte Carlo and photon mapping methods to provide efficient and consistent rendering of complex scenes with vanishing bias. The second original contribution is a probabilistic image-based filtering and sample clustering framework that provides high quality previews of global illumination whilst remaining aware of high frequency detail and features in geometry, materials and the incident illumination. As will be seen, the challenges of edge-aware noise reduction are numerous and long standing, particularly when identifying high frequency features in noisy illumination signals. Discontinuities such as hard shadows and glossy reflections are commonly overlooked by progressive filtering techniques, however by dividing path space into multiple layers, once again based on utilising path vertex data, the overlapping illumination of varying intensities, colours and frequencies is more effectively handled. Thus noise is removed from each layer independent of features present in the remaining path space, effectively preserving such features