Global Illumination Computation Research Articles

Clustered voxel real-time global illumination

Real-time global illumination is an extremely challenging problem because of its intrinsic complexity due to the interplay between complex geometry, multiple light bounces, and stringent real-time frame-rate requirements. In this paper, we present a new technique that enables the real-time computation of global illumination in generic scenes for diffuse surfaces and static geometry. Our technique combines a voxel-based representation of the scene, a voxel-clustering algorithm, and an iterative light-propagation algorithm based on the resulting clusters. Although our implementation is currently designed to handle the first (and main) bounce, the technique allows for multiple light bounces. Summing up all these components results in a flexible algorithm capable of providing global illumination effects and on-the-fly illumination computations.

Стан та перспективи подальших досліджень сфери обчислення глобального освітлення у реальному часі

Currently, computer graphics is a very important part of computer science. Graphics-related developments have been used in many different situations, for example, in animated and cinema movie productions, in computer graphics applications, modeling, and simulation systems, for different visualizations in medicine, mathematics, physics, etc. One of the main problems of computer graphics is the task of transforming the information of some imaginary scene and its observer into a photorealistic image of this scene for them. Solving this problem is very important, but right now obtaining a good quality result is possible only in a non-interactive scenario (for example, in animated films), while in real-time (for example, in computer modeling or simulations, in computer games) it is usually necessary to use some approximate algorithms. Although these algorithms are often able to provide a natural-looking result, they still have plenty of very noticeable inaccuracies. However, this topic is gaining more and more development recently due to the improvement of graphics processors. In addition to a significant increase in computation speed and the number of cores, the appearance of ray tracing hardware acceleration plays a large role. Global illumination computation is an inseparable part of photorealistic image generation. This paper is focused on solving this problem in real-time, which means developing a system capable of generating such images at a speed sufficient for the resulting sequence to be perceived by a person as a smooth animation. We give the theoretical information required for understanding this problem and describe existing methods and algorithms for solving it with their advantages and disadvantages. Also based on an overview of the topic's current state, we analyze further research prospects and directions for improving existing and developing new methods of real-time global illumination calculation, while considering compute power and technologies of the latest graphics hardware.

MIS compensation

Multiple importance sampling (MIS) has become an indispensable tool in Monte Carlo rendering, widely accepted as a near-optimal solution for combining different sampling techniques. But an MIS combination, using the common balance or power heuristics, often results in an overly defensive estimator, leading to high variance. We show that by generalizing the MIS framework, variance can be substantially reduced. Specifically, we optimize one of the combined sampling techniques so as to decrease the overall variance of the resulting MIS estimator. We apply the approach to the computation of direct illumination due to an HDR environment map and to the computation of global illumination using a path guiding algorithm. The implementation can be as simple as subtracting a constant value from the tabulated sampling density done entirely in a preprocessing step. This produces a consistent noise reduction in all our tests with no negative influence on run time, no artifacts or bias, and no failure cases.

Microfacet BSDFs Generated from NDFs and Explicit Microgeometry

Microfacet distributions are considered nowadays as a reference for physically plausible BSDF representations. Many authors have focused on their physical and mathematical correctness, while introducing means to enlarge the range of possible appearances. This article is dedicated to Normal Distribution Functions (NDFs) and the influence of their shape on the rendered material aspect. We provide a complete framework for studying the impact of NDFs on the observed Bidirectional Scattering Distribution Functions (BSDFs). To explore very general NDFs, manually controlled by the user, and including anisotropic materials, we propose to use a piecewise continuous representation. It is derived with its associated Smith shadowing-masking function and importance sampling formulations for ensuring efficient global illumination computations. A new procedure is also proposed in this article for generating an explicit geometric micro-surface, used to evaluate the validity of analytic models and multiple scattering effects. The results are produced with a computer-generated process using path tracing. They show that this generation procedure is suitable with any NDF model, independently from its shape complexity.

Real-Time Rendering with Lighting Grid Hierarchy

We present an extension of the lighting grid hierarchy method for real-time rendering with many lights on the GPU. We describe efficient methods for parallel construction of the lighting grid hierarchy and using it with deferred rending. We also present a method for estimating shadows from many lights with a small number of shadow samples using the ray tracing API on the GPU. We show how our approach can be used for real-time global illumination computation with virtual point lights.

Precomputed Multiple Scattering for Rapid Light Simulation in Participating Media.

Rendering translucent materials is costly: light transport algorithms need to simulate a large number of scattering events inside the material before reaching convergence. The cost is especially high for materials with a large albedo or a small mean-free-path, where higher-order scattering effects dominate. We present a new method for fast computation of global illumination with participating media. Our method uses precomputed multiple scattering effects, stored in two compact tables. These precomputed multiple scattering tables are easy to integrate with any illumination simulation algorithm. We give examples for virtual ray lights (VRL), photon mapping with beams and paths (UPBP), Metropolis Light Transport with Manifold Exploration (MEMLT). The original algorithms are in charge of low-order scattering, combined with multiple scattering computed using our table. Our results show significant improvements in convergence speed and memory costs, with negligible impact on accuracy.

Cloud Baking

We propose Cloud Baking, a collaborative rendering architecture for dynamic Web3D scenes. In our architecture, the cloud renderer renders the scene with the global illumination (GI) information in a GI map; the web-based client renderer renders the scene with ambient lighting only and blends it with the GI map received from the cloud for the final scene. This approach allows the users to interact with the web scene and change the scene dynamically through the web interface end, yet move the computationally heavy tasks of global illumination computation to the cloud. A challenge we face is the interaction delay that causes the frames rendered on the cloud and the client to go out of sync. We propose to use 3D warping and a hole-filling algorithm designed for GI map to predict the late GI map. We show both quantitatively and visually the quality of the GI map produced using our method. Our prediction algorithm allows us to further reduce the frequency at which the GI map is computed and sent from the server, reducing both computational needs and bandwidth usage.

Adaptive matrix column sampling and completion for rendering participating media

Several scalable many-light rendering methods have been proposed recently for the efficient computation of global illumination. However, gathering contributions of virtual lights in participating media remains an inefficient and time-consuming task. In this paper, we present a novel sparse sampling and reconstruction method to accelerate the gathering step of the many-light rendering for participating media. Our technique explores the observation that the scattered lightings are usually locally coherent and of low rank even in heterogeneous media. In particular, we first introduce a matrix formation with light segments as columns and eye ray segments as rows, and formulate the gathering step into a matrix sampling and reconstruction problem. We then propose an adaptive matrix column sampling and completion algorithm to efficiently reconstruct the matrix by only sampling a small number of elements. Experimental results show that our approach greatly improves the performance, and obtains up to one order of magnitude speedup compared with other state-of-the-art methods of many-light rendering for participating media.

An Error Estimation Framework for Many‐Light Rendering

AbstractThe popularity of many‐light rendering, which converts complex global illumination computations into a simple sum of the illumination from virtual point lights (VPLs), for predictive rendering has increased in recent years. A huge number of VPLs are usually required for predictive rendering at the cost of extensive computational time. While previous methods can achieve significant speedup by clustering VPLs, none of these previous methods can estimate the total errors due to clustering. This drawback imposes on users tedious trial and error processes to obtain rendered images with reliable accuracy. In this paper, we propose an error estimation framework for many‐light rendering. Our method transforms VPL clustering into stratified sampling combined with confidence intervals, which enables the user to estimate the error due to clustering without the costly computing required to sum the illumination from all the VPLs. Our estimation framework is capable of handling arbitrary BRDFs and is accelerated by using visibility caching, both of which make our method more practical. The experimental results demonstrate that our method can estimate the error much more accurately than the previous clustering method.

Ray tracing-based interactive diffuse indirect illumination

Despite great efforts in recent years to accelerate global illumination computation, the real-time ray tracing of fully dynamic scenes to support photorealistic indirect illumination effects has ye...

Irradiance regression for efficient final gathering in global illumination

Photon mapping is widely used for global illumination rendering because of its high computational efficiency. But its efficiency is still limited mainly by the intensive sampling required in final gathering a process that is critical for removing low frequency artifacts of density estimation. In this paper we propose a method to predict the final gathering estimation with direct density estimation thereby achieving high quality global illumination by photon mapping with high efficiency. We first sample the irradiance of a subset of shading points by both final gathering and direct radiance estimation. Then we use the samples as a training set to predict the final gathered irradiance of other shading points through regression. Consequently we are able to achieve about three times overall speedup compared with straightforward final gathering in global illumination computation with the same rendering quality.

Distributed Out‐of‐Core Stochastic Progressive Photon Mapping

AbstractAt present, stochastic progressive photon mapping (SPPM) is one of the most comprehensive methods for a consistent global illumination computation. Even though the number of photons is unlimited due to their progressive nature, the scene size is still bound by the available main memory. In this paper, we present the first consistent out‐of‐core SPPM algorithm. In order to cope with large scenes, we automatically subdivide the geometry and parallelly trace photons and eye rays in a portal‐based system, distributed across multiple machines in a commodity cluster. Moreover, modifications of the original SPPM method are introduced that keep both the utilization of tracer machines high and the network traffic low. Therefore, compared to a portal‐based single machine setup, our distributed approach achieves a significant speedup. We compare a GPU‐based with a CPU‐based implementation and demonstrate our system in multiple large test scenes of up to 90 million triangles.

Scalable Realistic Rendering with Many‐Light Methods

AbstractRecent years have seen increasing attention and significant progress in many‐light rendering, a class of methods for efficient computation of global illumination. The many‐light formulation offers a unified mathematical framework for the problem reducing the full lighting transport simulation to the calculation of the direct illumination from many virtual light sources. These methods are unrivaled in their scalability: they are able to produce plausible images in a fraction of a second but also converge to the full solution over time. In this state‐of‐the‐art report, we give an easy‐to‐follow, introductory tutorial of the many‐light theory; provide a comprehensive, unified survey of the topic with a comparison of the main algorithms; discuss limitations regarding materials and light transport phenomena and present a vision to motivate and guide future research. We will cover both the fundamental concepts as well as improvements, extensions and applications of many‐light rendering.

The State of the Art in Interactive Global Illumination

AbstractThe interaction of light and matter in the world surrounding us is of striking complexity and beauty. Since the very beginning of computer graphics, adequate modelling of these processes and efficient computation is an intensively studied research topic and still not a solved problem. The inherent complexity stems from the underlying physical processes as well as the global nature of the interactions that let light travel within a scene. This paper reviews the state of the art in interactive global illumination (GI) computation, i.e., methods that generate an image of a virtual scene in less than 1 s with an as exact as possible, or plausible, solution to the light transport. Additionally, the theoretical background and attempts to classify the broad field of methods are described. The strengths and weaknesses of different approaches, when applied to the different visual phenomena, arising from light interaction are compared and discussed. Finally, the paper concludes by highlighting design patterns for interactive GI and a list of open problems.

Guided Image Filtering for Interactive High‐quality Global Illumination

AbstractInteractive computation of global illumination is a major challenge in current computer graphics research. Global illumination heavily affects the visual quality of generated images. It is therefore a key attribute for the perception of photo‐realistic images. Path tracing is able to simulate the physical behaviour of light using Monte Carlo techniques. However, the computational burden of this technique prohibits interactive rendering times on standard commodity hardware in high‐quality. Trying to solve the Monte Carlo integration with fewer samples results in characteristic noisy images. Global illumination filtering methods take advantage of the fact that the integral for neighbouring pixels may be very similar. Averaging samples of similar characteristics in screen‐space may approximate the correct integral, but may result in visible outliers. In this paper, we present a novel path tracing pipeline based on an edge‐aware filtering method for the indirect illumination which produces visually more pleasing results without noticeable outliers. The key idea is not to filter the noisy path traced images but to use it as a guidance to filter a second image composed from characteristic scene attributes that do not contain noise by default. We show that our approach better approximates the Monte Carlo integral compared to previous methods. Since the computation is carried out completely in screen‐space it is therefore applicable to fully dynamic scenes, arbitrary lighting and allows for high‐quality path tracing at interactive frame rates on commodity hardware.

Hierarchical Radiosity for Multiresolution Systems Based on Normal Tests

The hierarchical radiosity algorithm provides high-quality illumination and the view-independent results obtained can be re-employed for different camera positions. On the other hand, the utilization of multiresolution models is a common solution for the real-time rendering of complex scenes. In this case, the level of detail of each object depends on the specific camera position. Unfortunately, global illumination computations may present an important performance loss in this context. In this paper we present a new solution for hierarchical radiosity for multiresolution systems. Our proposal is based on the application of an enriched hierarchical radiosity algorithm to an input scene with low-resolution objects (represented by coarse meshes) and the efficient data management of the resulting values. The representation of the information we use permits the application of the radiosity values obtained for the coarse version of an object to finer resolution versions of that object. Results of our implementation show that our algorithm produces high-quality images with an important reduction in computational costs.

Spatial Directional Radiance Caching

AbstractWe present a new approach for accelerated global illumination computation in scenes with glossy surfaces. Our algorithm combines sparse illumination computation used in the radiance caching algorithm with BRDF importance sampling. To make this approach feasible, we extend the idea of lazy illumination evaluation, used in the caching approaches, from the spatial to the directional domain. Using importance sampling allows us to apply caching not only on low‐gloss but also on shiny materials with high‐frequency BRDFs, for which the radiance caching algorithm breaks down.

Practical Global Illumination with Irradiance Caching

Irradiance caching is a ray tracing-based technique for computing global illumination on diffuse surfaces. Specifically, it addresses the computation of indirect illumination bouncing off one diffuse object onto another. The sole purpose of irradiance caching is to make this computation reasonably fast. The main idea is to perform the indirect illumination sampling only at a selected set of locations in the scene, store the results in a cache, and reuse the cached value at other points through fast interpolation. This book is for anyone interested in making a production-ready implementation of irradiance caching that reliably renders artifact-free images. Since its invention 20 years ago, the irradiance caching algorithm has been successfully used to accelerate global illumination computation in the Radiance lighting simulation system. Its widespread use had to wait until computers became fast enough to consider global illumination in film production rendering. Since then, its use is ubiquitous. Virtually all commercial and open-source rendering software base the global illumination computation upon irradiance caching. Although elegant and powerful, the algorithm in its basic form often fails to produce artifact-free mages. Unfortunately, practical information on implementing the algorithm is scarce. The main objective of this book is to show the irradiance caching algorithm along with all the details and tricks upon which the success of its practical implementation is dependent. In addition, we discuss some extensions of the basic algorithm, such as a GPU implementation for interactive global illumination computation and temporal caching that exploits temporal coherence to suppress flickering in animations. Our goal is to show the material without being overly theoretical. However, the reader should have some basic understanding of rendering concepts, ray tracing in particular. Familiarity with global illumination is useful but not necessary to read this book.

Temporal Radiance Caching

We present a novel method for fast, high quality computation of glossy global illumination in animated environments. Building on the irradiance caching and radiance caching algorithms, our method leverages temporal coherence by sparse temporal sampling and interpolation of the indirect lighting. In our approach, part of the global illumination solution computed in previous frames is reused in the current frame. Our reusing scheme adapts to the change of incoming radiance by updating the indirect lighting only where there is a significant change. By reusing data in several frames, our method removes the flickering artifacts and yields a significant speedup compared to classical computation in which a new cache is computed for every frame. We also define temporal gradients for smooth temporal interpolation. A key aspect of our method is the absence of any additional complex data structure, making the implementation into any existing renderer based on irradiance and radiance caching straightforward. We describe the implementation of our method using graphics hardware for improved performance.

Parallel selective rendering of high-fidelity virtual environments

Physically-based computer graphics offers the potential of achieving high-fidelity virtual environments in which the propagation of light in real environments is accurately simulated. However, such global illumination computations for even simple scenes may take many seconds and even longer to render a single frame, currently precluding their use in any interactive virtual environment, which requires many frames per second. Parallel processing is one solution, but it simply may not be feasible to have sufficient processors available. Furthermore, even if a suitably sized cluster is present, the overheads associated with parallel rendering may begin to dominate restricting the parallel solution to a subset of the cluster. The human visual system (HVS) provides us with our visual sensory input, but while the HVS is good, it is not perfect. If we wish to invoke, in a virtual environment, the same perceptual response in viewers as if they were actually there in the real scene, then only those parts of an environment that are actually attended to by a viewer at any point of time need be calculated at the highest quality. The remainder of the image can be calculated at a much lower quality, and with much less computational expense, without the user being aware of this quality difference. This paper presents a rendering framework which exploits parallel processing and knowledge of the human visual system to provide a means of rendering high-fidelity virtual environments.