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

Towards Predictive Rendering in Virtual Reality

The strive for generating predictive images, i.e., images representing radiometrically correct renditions of reality, has been a longstanding problem in computer graphics. The exactness of such images is extremely important for Virtual Reality applications like Virtual Prototyping, where users need to make decisions impacting large investments based on the simulated images. Unfortunately, generation of predictive imagery is still an unsolved problem due to manifold reasons, especially if real-time restrictions apply. First, existing scenes used for rendering are not modeled accurately enough to create predictive images. Second, even with huge computational efforts existing rendering algorithms are not able to produce radiometrically correct images. Third, current display devices need to convert rendered images into some low-dimensional color space, which prohibits display of radiometrically correct images. Overcoming these limitations is the focus of current state-of-the-art research. This thesis also contributes to this task. First, it briefly introduces the necessary background and identifies the steps required for real-time predictive image generation. Then, existing techniques targeting these steps are presented and their limitations are pointed out. To solve some of the remaining problems, novel techniques are proposed. They cover various steps in the predictive image generation process, ranging from accurate scene modeling over efficient data representation to high-quality, real-time rendering. A special focus of this thesis lays on real-time generation of predictive images using bidirectional texture functions (BTFs), i.e., very accurate representations for spatially varying surface materials. The techniques proposed by this thesis enable efficient handling of BTFs by compressing the huge amount of data contained in this material representation, applying them to geometric surfaces using texture and BTF synthesis techniques, and rendering BTF covered objects in real-time. Further approaches proposed in this thesis target inclusion of real-time global illumination effects or more efficient rendering using novel level-of-detail representations for geometric objects. Finally, this thesis assesses the rendering quality achievable with BTF materials, indicating a significant increase in realism but also confirming the remainder of problems to be solved to achieve truly predictive image generation

Tensor approximation in visualization and graphics

In this course, we will introduce the basic concepts of tensor approximation (TA) – a higher-order generalization of the SVD and PCA methods – as well as its applications to visual data representation, analysis and visualization, and bring the TA framework closer to visualization and computer graphics researchers and practitioners. The course will cover the theoretical background of TA methods, their properties and how to compute them, as well as practical applications of TA methods in visualization and computer graphics contexts. In a first theoretical part, the attendees will be instructed on the necessary mathematical background of TA methods to learn the basics skills of using and applying these new tools in the context of the representation of large multidimensional visual data. Specific and very noteworthy features of the TA framework are highlighted which can effectively be exploited for spatio-temporal multidimensional data representation and visualization purposes. In two application oriented sessions, compact TA data representation in scientific visualization and computer graphics as well as decomposition and reconstruction algorithms will be demonstrated. At the end of the course, the participants will have a good basic knowledge of TA methods along with a practical understanding of its potential application in visualization and graphics related projects

Efficient Streaming of 3D Scenes with Complex Geometry and Complex Lighting

International audienceStreaming data to efficiently render complex 3D scenes in presence of global illumination is still a challenging task. In this paper, we introduce a new data structure based on a 3D grid of irradiance vectors to store the indirect illumination appearing on complex and detailed objects: the Irradiance Vector Grid (IVG). This representation is independent of the geometric complexity and is suitable for quantization to different quantization schemes. Moreover, its streaming over network involves only a small overhead compared to detailed geometry, and can be achieved independently of the geometry. Furthermore, it can be efficiently rendered using modern graphics hardware. We demonstrate our new data structure in a new remote 3D visualization system, that integrates indirect lighting streaming and progressive transmission of the geometry, and study the impact of different strategies on data transfer

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

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

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