The Iray Light Transport Simulation and Rendering System

While ray tracing has become increasingly common and path tracing is well understood by now, a major challenge lies in crafting an easy-to-use and efficient system implementing these technologies. Following a purely physically-based paradigm while still allowing for artistic workflows, the Iray light transport simulation and rendering system allows for rendering complex scenes by the push of a button and thus makes accurate light transport simulation widely available. In this document we discuss the challenges and implementation choices that follow from our primary design decisions, demonstrating that such a rendering system can be made a practical, scalable, and efficient real-world application that has been adopted by various companies across many fields and is in use by many industry professionals today

Many-Light Real-Time Global Illumination using Sparse Voxel Octree

Global illumination (GI) rendering simulates the propagation of light through a 3D volume and its interaction with surfaces, dramatically increasing the fidelity of computer generated images. While off-line GI algorithms such as ray tracing and radiosity can generate physically accurate images, their rendering speeds are too slow for real-time applications. The many-light method is one of many novel emerging real-time global illumination algorithms. However, it requires many shadow maps to be generated for Virtual Point Light (VPL) visibility tests, which reduces its efficiency. Prior solutions restrict either the number or accuracy of shadow map updates, which may lower the accuracy of indirect illumination or prevent the rendering of fully dynamic scenes. In this thesis, we propose a hybrid real-time GI algorithm that utilizes an efficient Sparse Voxel Octree (SVO) ray marching algorithm for visibility tests instead of the shadow map generation step of the many-light algorithm. Our technique achieves high rendering fidelity at about 50 FPS, is highly scalable and can support thousands of VPLs generated on the fly. A survey of current real-time GI techniques as well as details of our implementation using OpenGL and Shader Model 5 are also presented

Second-Order Occlusion-Aware Volumetric Radiance Caching

We present a second-order gradient analysis of light transport in participating media and use this to develop an improved radiance caching algorithm for volumetric light transport. We adaptively sample and interpolate radiance from sparse points in the medium using a second-order Hessian-based error metric to determine when interpolation is appropriate. We derive our metric from each point's incoming light field, computed by using a proxy triangulation-based representation of the radiance reflected by the surrounding medium and geometry. We use this representation to efficiently compute the first- and second-order derivatives of the radiance at the cache points while accounting for occlusion changes. We also propose a self-contained two-dimensional model for light transport in media and use it to validate and analyze our approach, demonstrating that our method outperforms previous radiance caching algorithms both in terms of accurate derivative estimates and final radiance extrapolation. We generalize these findings to practical three-dimensional scenarios, where we show improved results while reducing computation time by up to 30\% compared to previous work

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

GPU 상에서의 빠르고 가벼운 Path Guiding 알고리즘

학위논문(석사) -- 서울대학교대학원 : 공과대학 전기·정보공학부, 2022.2. 김영민.We propose a simple, yet practical path guiding algorithm that runs on GPU. Path guiding renders photo-realistic images by simulating the iterative bounces of rays, which are sampled from the radiance distribution. The radiance distribution is often learned by serially updating the hierarchical data structure to represent complex scene geometry, which is not easily implemented with GPU. In contrast, we employ a regular data structure and allow fast updates by processing a significant number of rays with GPU. We further increase the efficiency of radiance learning by employing SARSA used in reinforcement learning. SARSA does not include aggregation of incident radiance from all directions nor storing all of the previous paths. The learned distribution is then importance-sampled with an optimized rejection sampling, which adapts the current surface normal to reflect finer geometry than the grid resolution. All of the algorithms have been implemented on GPU using megakernal architecture with NVIDIA OptiX. Through numerous experiments on complex scenes, we demonstrate that our proposed path guiding algorithm works efficiently on GPU, drastically reducing the number of wasted paths.본 연구는 GPU 상에서 작동하는 간단하지만 효과적인 path guiding 알고리즘을 제안한다. Path guiding은 path tracing의 노이즈를 줄이기 위해 제안된 기법으로 샘플링 과정에서 복사 휘도(radiance)를 배우고 이를 이용해 중요도 샘플링(importance sampling)을 수행한다. 복사 휘도의 복잡한 분포를 배우기 위해 이전의 논문들에서는 복잡한 재귀적 데이터 구조를 제안하고 이를 순차적으로 업데이트 하였지만 이는 CPU상에서의 path tracing만을 가정한 것으로 GPU상에서는 쉽게 구현하기 어려우며 효과적으로 작동하지 않는다. 본 논문에서는 GPU 친화적인 간단한 그리드 형태의 데이터를 사용해 path guiding 알고리즘을 진행하였다. 또한 path guiding의 두 가지 목표-(1) 복사 휘도 학습과 (2) 학습된 복사 휘도 분포를 이용한 중요도 샘플링-를 GPU 상에서 효과적으로 구현하기 위해 다음과 같은 방법을 제시한다. 우선 복사 휘도 학습의 경우, 강화학습과 복사 휘도 학습의 구조적 유사성을 밝힌 이전 연구를 확장하여 가볍고 빠른 SARSA를 이용한 학습 방법을 제안하였다. 학습된 복사 휘도는 공간-방향을 그리드 형태로 분할한 GPU상의 데이터 구조에 저장된다. 학습된 복사 휘도를 사용한 중요도 샘플링의 경우 법선 벡터 방향에 유효하지 않은 샘플들은 제외한 뒤, 리젝션 샘플링(rejection sampling)을 이용해 중요도 샘플링(importance sampling)을 수행하였다. 모든 알고리즘은 NVIDIA OptiX를 사용해 GPU상에서 megakernel 구조로 구현되었다. 복잡한 구조의 씬 데이터에 대해 여러 번 실험을 수행하였으며 본 연구에서 제안한 방법의 우수성을 확인하였다.Abstract i Chapter 1 Introduction 1 Chapter 2 Background and Related Works 4 2.1 Ray Tracing on GPU 4 2.2 Path Guiding 5 2.3 Reinforcement Learning and Light Transport 6 Chapter 3 Problem Setting and Overview 7 Chapter 4 Fast and Lightweight Radiance Learning 10 4.1 Analogy between the Rendering Equation and Reinforcement Learning 10 4.2 Fast and Lightweight Radiance Learning with SARSA 12 Chapter 5 Efficient Importance Sampling from Learned Radiance 16 5.1 Importance Sampling on Hemispherical Domain 16 5.2 Fast and Efficient Importance Sampling with Optimized Rejection Sampling 18 5.3 Normalizing Term Calculation with Memoization 20 Chapter 6 Experiments and Results 22 6.1 GPU-based Path Guiding with a Regular Grid 23 6.2 Comparison for Radiance Learning Methods 25 6.3 Comparison for Radiance Sampling Methods 27 Chapter 7 Conclusion 35 Appendix A Additional Experimental Results 36 A.1 Comparison for Spatial Directional Resolution 36 A.2 Equal SPP Comparison 36 Appendix B Pseudocode for the Algorithm 39 초록 46 Acknowledgements 47석

Ensemble metropolis light transport

This article proposes a Markov Chain Monte Carlo (MCMC) rendering algorithm based on a family of guided transition kernels. The kernels exploit properties of ensembles of light transport paths, which are distributed according to the lighting in the scene, and utilize this information to make informed decisions for guiding local path sampling. Critically, our approach does not require caching distributions in world space, saving time and memory, yet it is able to make guided sampling decisions based on whole paths. We show how this can be implemented efficiently by organizing the paths in each ensemble and designing transition kernels for MCMC rendering based on a carefully chosen subset of paths from the ensemble. This algorithm is easy to parallelize and leads to improvements in variance when rendering a variety of scenes

Planckian dissipation, minimal viscosity and the transport in cuprate strange metals

Could it be that the matter from the electrons in high Tc superconductors is of a radically new kind that may be called "many body entangled compressible quantum matter"? Much of this text is intended as an easy to read tutorial, explaining recent theoretical advances that have been unfolding at the cross roads of condensed matter- and string theory, black hole physics as well as quantum information theory. These developments suggest that the physics of such matter may be governed by surprisingly simple principles. My real objective is to present an experimental strategy to test critically whether these principles are actually at work, revolving around the famous linear resistivity characterizing the strange metal phase. The theory suggests a very simple explanation of this "unreasonably simple" behavior that is actually directly linked to remarkable results from the study of the quark gluon plasma formed at the heavy ion colliders: the "fast hydrodynamization" and the "minimal viscosity". This leads to high quality predictions for experiment: the momentum relaxation rate governing the resistivity relates directly to the electronic entropy, while at low temperatures the electron fluid should become unviscous to a degree that turbulent flows can develop even on the nanometre scale.Comment: 23 pages, no figures. Submission to SciPos