Doctor of Philosophy

dissertationReal-time global illumination is the next frontier in real-time rendering. In an attempt to generate realistic images, games have followed the film industry into physically based shading and will soon begin integrating global illumination techniques. Traditional methods require too much memory and too much time to compute for real-time use. With Modular and Delta Radiance Transfer we precompute a scene-independent, low-frequency basis that allows us to calculate complex indirect lighting calculations in a much lower dimensional subspace with a reduced memory footprint and real-time execution. The results are then applied as a light map on many different scenes. To improve the low frequency results, we also introduce a novel screen space ambient occlusion technique that allows us to generate a smoother result with fewer samples. These three techniques, low and high frequency used together, provide a viable indirect lighting solution that can be run in milliseconds on today's hardware, providing a useful new technique for indirect lighting in real-time graphics

Vector occluders: an empirical approximation for rendering global illumination effects in real-time

Precomputation has been previously used as a means to get global illumination effects in real-time on consumer hardware of the day. Our work uses Sloan???s 2002 PRT method as a starting point, and builds on it with two new ideas. We first explore an alternative representation for PRT data. ???Cpherical harmonics??? (CH) are introduced as an alternative to spherical harmonics, by substituting the Chebyshev polynomial in the place of the Legendre polynomial as the orthogonal polynomial in the spherical harmonics definition. We show that CH can be used instead of SH for PRT with near-equivalent performance. ???Vector occluders??? (VO) are introduced as a novel, precomputed, real-time, empirical technique for adding global illumination effects including shadows, caustics and interreflections to a locally illuminated scene on static geometry. VO encodes PRT data as simple vectors instead of using SH. VO can handle point lights, whereas a standard SH implementation cannot

Parallel progressive precomputed radiance transfer

Precomputed Radiance Transport (PRT) was introduced as a technique to enable interactive navigation and distant environmental real time relighting of rigid scenes. Evaluating radiance transport is, however, a computationally very demanding task, which precludes PRT's utilization during the model design phase, since the user must wait for long periods of time before being able to light and navigate within the model. This paper proposes and validates an approach to provide visual feedback to the user as soon as possible, within PRT context. By resorting to parallel processing and progressive refinement, the user is quickly presented with a lower lighting resolution of the virtual model. This is then progressively refined by incrementally increasing the number of incident directions taken into account on transport computations. PRT is, however, a complex algorithm that requires frequent collective communications of huge volumes of data, thus constraining the maximum achievable speedup on a parallel system. This issue is analysed and an alternative workload distribution is proposed and evaluated on a 12 node dual processor cluster. The final solution ensures a good resource utilization rate, reducing response times from dozens of seconds to a few hundred milliseconds.Fundação para a Ciências e a Tecnologia - Project SEARCH - SErvices and Advanced Research Computing with HTC/HPC clusters

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

Theory and algorithms for efficient physically-based illumination

Realistic image synthesis is one of the central fields of study within computer graphics. This thesis treats efficient methods for simulating light transport in situations where the incident illumination is produced by non-pointlike area light sources and distant illumination described by environment maps. We describe novel theory and algorithms for physically-based lighting computations, and expose the design choices and tradeoffs on which the techniques are based. Two publications included in this thesis deal with precomputed light transport. These techniques produce interactive renderings of static scenes under dynamic illumination and full global illumination effects. This is achieved through sacrificing the ability to freely deform and move the objects in the scene. We present a comprehensive mathematical framework for precomputed light transport. The framework, which is given as an abstract operator equation that extends the well-known rendering equation, encompasses a significant amount of prior work as its special cases. We also present a particular method for rendering objects in low-frequency lighting environments, where increased efficiency is gained through the use of compactly supported function bases. Physically-based shadows from area and environmental light sources are an important factor in perceived image realism. We present two algorithms for shadow computation. The first technique computes shadows cast by low-frequency environmental illumination on animated objects at interactive rates without requiring difficult precomputation or a priori knowledge of the animations. Here the capability to animate is gained by forfeiting indirect illumination. Another novel shadow algorithm for off-line rendering significantly enhances a previous physically-based soft shadow technique by introducing an improved spatial hierarchy that alleviates redundant computations at the cost of using more memory. This thesis advances the state of the art in realistic image synthesis by introducing several algorithms that are more efficient than their predecessors. Furthermore, the theoretical contributions should enable the transfer of ideas from one particular application to others through abstract generalization of the underlying mathematical concepts.Tämä tutkimus käsittelee realististen kuvien syntetisointia tietokoneella tilanteissa, jossa virtuaalisen ympäristön valonlähteet ovat fysikaalisesti mielekkäitä. Fysikaalisella mielekkyydellä tarkoitetaan sitä, että valonlähteet eivät ole idealisoituja eli pistemäisiä, vaan joko tavanomaisia pinta-alallisia valoja tai kaukaisia ympäristövalokenttiä (environment maps). Väitöskirjassa esitetään uusia algoritmeja, jotka soveltuvat matemaattisesti perusteltujen valaistusapproksimaatioiden laskentaan erilaisissa käyttötilanteissa. Esilaskettu valonkuljetus on yleisnimi reaaliaikaisille menetelmille, jotka tuottavat kuvia staattisista ympäristöistä siten, että valaistus voi muuttua ajon aikana vapaasti ennalta määrätyissä rajoissa. Tässä työssä esitetään esilasketulle valonkuljetukselle kattava matemaattinen kehys, joka selittää erikoistapauksinaan suuren määrän aiempaa tutkimusta. Kehys annetaan abstraktin lineaarisen operaattoriyhtälön muodossa, ja se yleistää tunnettua kuvanmuodostusyhtälöä (rendering equation). Työssä esitetään myös esilasketun valonkuljetuksen algoritmi, joka parantaa aiempien vastaavien menetelmien tehokkuutta esittämällä valaistuksen funktiokannassa, jonka ominaisuuksien vuoksi ajonaikainen laskenta vähenee huomattavasti. Fysikaalisesti mielekkäät valonlähteet tuottavat pehmeäreunaisia varjoja. Työssä esitetään uusi algoritmi pehmeiden varjojen laskemiseksi liikkuville ja muotoaan muuttaville kappaleille, joita valaisee matalataajuinen ympäristövalokenttä. Useimmista aiemmista menetelmistä poiketen algoritmi ei vaadi esitietoa siitä, kuinka kappale voi muuttaa muotoaan ajon aikana. Muodonmuutoksen aiheuttaman suuren laskentakuorman vuoksi epäsuoraa valaistusta ei huomioida. Työssä esitetään myös toinen uusi algoritmi pehmeiden varjojen laskemiseksi, jossa aiemman varjotilavuuksiin (shadow volumes) perustuvan algoritmin tehokkuutta parannetaan merkittävästi uuden hierarkkisen avaruudellisen hakurakenteen avulla. Uusi rakenne vähentää epäoleellista laskentaa muistinkulutuksen kustannuksella. Työssä esitetään aiempaa tehokkaampia algoritmeja fysikaalisesti perustellun valaistuksen laskentaan. Niiden lisäksi työn esilaskettua valonkuljetusta koskevat teoreettiset tulokset yleistävät suuren joukon aiempaa tutkimusta ja mahdollistavat näin ideoiden siirron erityisalalta toiselle.reviewe

A Real-time Method for Inserting Virtual Objects into Neural Radiance Fields

We present the first real-time method for inserting a rigid virtual object into a neural radiance field, which produces realistic lighting and shadowing effects, as well as allows interactive manipulation of the object. By exploiting the rich information about lighting and geometry in a NeRF, our method overcomes several challenges of object insertion in augmented reality. For lighting estimation, we produce accurate, robust and 3D spatially-varying incident lighting that combines the near-field lighting from NeRF and an environment lighting to account for sources not covered by the NeRF. For occlusion, we blend the rendered virtual object with the background scene using an opacity map integrated from the NeRF. For shadows, with a precomputed field of spherical signed distance field, we query the visibility term for any point around the virtual object, and cast soft, detailed shadows onto 3D surfaces. Compared with state-of-the-art techniques, our approach can insert virtual object into scenes with superior fidelity, and has a great potential to be further applied to augmented reality systems

Interactive display of isosurfaces with global illumination

Journal ArticleAbstract-In many applications, volumetric data sets are examined by displaying isosurfaces, surfaces where the data, or some function of the data, takes on a given value. Interactive applications typically use local lighting models to render such surfaces. This work introduces a method to precompute or lazily compute global illumination to improve interactive isosurface renderings. The precomputed illumination resides in a separate volume and includes direct light, shadows, and interreflections. Using this volume, interactive globally illuminated renderings of isosurfaces become feasible while still allowing dynamic manipulation of lighting, viewpoint and isovalue