Adam Arbree

Lightcuts: a scalable approach to illumination

Lightcuts is a scalable framework for computing realistic illumination. It handles arbitrary geometry, non-diffuse materials, and illumination from a wide variety of sources including point lights, area lights, HDR environment maps, sun/sky models, and indirect illumination. At its core is a new algorithm for accurately approximating illumination from many point lights with a strongly sublinear cost. We show how a group of lights can be cheaply approximated while bounding the maximum approximation error. A binary light tree and perceptual metric are then used to adaptively partition the lights into groups to control the error vs. cost tradeoff.We also introduce reconstruction cuts that exploit spatial coherence to accelerate the generation of anti-aliased images with complex illumination. Results are demonstrated for five complex scenes and show that lightcuts can accurately approximate hundreds of thousands of point lights using only a few hundred shadow rays. Reconstruction cuts can reduce the number of shadow rays to tens.

Multidimensional lightcuts

Multidimensional lightcuts is a new scalable method for efficiently rendering rich visual effects such as motion blur, participating media, depth of field, and spatial anti-aliasing in complex scenes. It introduces a flexible, general rendering framework that unifies the handling of such effects by discretizing the integrals into large sets of gather and light points and adaptively approximating the sum of all possible gather-light pair interactions.We create an implicit hierarchy, the product graph, over the gather-light pairs to rapidly and accurately approximate the contribution from hundreds of millions of pairs per pixel while only evaluating a tiny fraction (e.g., 200--1,000). We build upon the techniques of the prior Lightcuts method for complex illumination at a point, however, by considering the complete pixel integrals, we achieve much greater efficiency and scalability.Our example results demonstrate efficient handling of volume scattering, camera focus, and motion of lights, cameras, and geometry. For example, enabling high quality motion blur with 256x temporal sampling requires only a 6.7x increase in shading cost in a scene with complex moving geometry, materials, and illumination.

Scalable Realistic Rendering with Many-Light Methods

Recent 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.

Measuring and modeling the appearance of finished wood

Wood coated with transparent finish has a beautiful and distinctive appearance that is familiar to everyone. Woods with unusual grain patterns. such as tiger, burl, and birdseye figures, have a strikingly unusual directional reflectance that is prized for decorative applications. With new, high resolution measurements of spatially varying BRDFs. we show that this distinctive appearance is due to light scattering that does not conform to the usual notion of anisotropic surface reflection. The behavior can be explained by scattering from the matrix of wood fibers below the surface, resulting in a subsurface highlight that occurs on a cone with an out-of-plane axis. We propose a new shading model component to handle reflection from subsurface fibers, which is combined with the standard diffuse and specular components to make a complete shading model. Rendered results from fits of our model to the measurement data demonstrate that this new model captures the distinctive appearance of wood.

Geometric constraints within feature hierarchies

We study the problem of enabling general 2D and 3D variational constraint representation to be used in conjunction with a feature hierarchy representation, where some of the features may use procedural or other non-constraint based representations. We trace the challenge to a requirement on constraint decomposition algorithms or decomposition-recombination (DR) planners used by most variational constraint solvers, formalize the feature hierarchy incorporation problem for DR-planners, clarify its relationship to other problems, and provide an efficient algorithmic solution. The new algorithms have been implemented in the general, 2D and 3D opensource geometric constraint solver FRONTIER developed at the University of Florida.

Heterogeneous Subsurface Scattering Using the Finite Element Method

Materials with visually important heterogeneous subsurface scattering, including marble, skin, leaves, and minerals are common in the real world. However, general, accurate, and efficient rendering of these materials is an open problem. In this paper, we describe a finite element (FE) solution of the heterogeneous diffusion equation (DE) that solves this problem. Our algorithm is the first to use the FE method to solve the difficult problem of heterogeneous subsurface rendering. To create our algorithm, we make two contributions. First, we correct previous work and derive an accurate and complete heterogeneous diffusion formulation with two key elements: the diffusive source boundary condition (DSBC)-an accurate model of the reduced intensity (RI) source-and its associated render query function. Second, we solve this formulation accurately and efficiently using the FE method. With these contributions, we can render subsurface scattering with a simple four step algorithm. To demonstrate that our algorithm is simultaneously general, accurate, and efficient, we test its performance on a series of difficult scenes. For a wide range of materials and geometry, it produces, in minutes, images that match path traced references, that required hours.

Single-pass Scalable Subsurface Rendering with Lightcuts

This paper presents a new, scalable, single pass algorithm for computing subsurface scattering using the diffusion approximation. Instead of pre‐computing a globally conservative estimate of the surface irradiance like previous two pass methods, the algorithm simultaneously refines hierarchical and adaptive estimates of both the surface irradiance and the subsurface transport. By using an adaptive, top‐down refinement method, the algorithm directs computational effort only to simulating those eye‐surface‐light paths that make significant contributions to the final image. Because the algorithm is driven by image importance, it scales more efficiently than previous methods that have a linear dependence on translucent surface area. We demonstrate that in scenes with many translucent objects and in complex lighting environments, our new algorithm has a significant performance advantage.

Solution space navigation for geometric constraint systems

We study the well documented problem of systematically navigating the potentially exponentially many roots or realizations of well-constrained, variational geometric constraint systems. We give a scalable method called the Equation and Solution Manager (ESM) that can be used both for automatic searches and visual, user-driven searches for desired realizations. The method incrementally assembles the desired solution of the entire system and avoids combinatorial explosion by offering the user a visual walk-through of the solutions to recursively constructed subsystems and by permitting the user to make gradual, adaptive solution choices.We isolate requirements on companion methods that are essential and desirable for efficient, meaningful solution space navigation. Specifically, they permit (a) incorporation of many existing approaches to solution space steering or navigation into the ESM; and (b) integration of the ESM into a standard geometric constraint solver architecture. We address the latter challenge and explain how the integration is achieved. Additionally, we sketch the ESM implementation as part of an opensource, 2D and 3D geometric constraint solver, FRONTIER.

FRONTIER: fully enabling geometric constraints for feature-based modeling and assembly

In the full paper [1], we discuss the functionality and implementation challenges of the Frontier geometric constraint engine, designed to address the main reasons for the underutilization of geometric constraints in todays 3D design and assembly systems. Here, we motivate the full paper by outlining the advantages of Frontier. Frontier fully enables both (a) the use of complex, cyclic, spatial constraint structures as well as (b) feature-based design. To deal with Issue (a), Frontier relies on the efficient generation of a close-to-optimal decomposition and recombination (DR) plan for completely general variational constraint systems (see Figure 1). A serious bouleneck in constraint solving is the exponential time dependence on the size of the largest system that is simultaneously solved by the algebraic-numeric solver. In most naturally occurring cases, Frontiers DR-plan is guaranteed in minimize this size (to within a small constant factor). To deal with Issue (b), Frontiers DR-plan admits the independent and local manipulation of features and sub-assemblies in one or more underlying feature hierarchies that are input (Figures 1 and 2). A DR-plan satisfying the above requirements is generated by the new Frontsier vertex Algorithm (FA): the DR problem and its significance as well as FA and its performance with respect to several relevant and newly formalized abstract measures are described in [2, 3]. Frontier employs a crucial representation of the DR-plans subsystems or clusters, their hierarchy and their interaction This representation merges network flow information, as well as other geometric and combinatorial information in a natural manner. Some of this information is obtained from an efficient flow-based algorithm for detecting small rigid sub-systems presented in [4]. The clarity of this representation is crucial in the concrete realization of FAs formal performance. More significantly, this representation allows Frontier to take advantage of its DR-plan in surprising and unsuspected ways listed below.

Optimizing realistic rendering with many-light methods

With recent improvements in hardware performance, there has been an increased demand in various industries, including game development, film production, and architectural visualization, for realistic image rendering with global illumination (GI). But current algorithms can not fulfill the strict speed and quality requirements of modern applications. Many-light rendering solves this problem. By reducing light-transport simulation to rendering the scene with many light sources, the many-light formulation offers a unified view of the global-illumination scene. Unlike other GI algorithms, the quality-speed trade-off in the many-light methods produces artifact-free images in a fraction of a second while converging to the full GI solution over time. This course presents a coherent summary of the state of the art in many-light rendering. It covers the basic many-light formulation and recent work on its use for computing global illumination in real time, on improving scalability with a large number of lights, on using the many-light method as a basis for a full GI solution, and on rendering participating media. The course focuses on the clarity of the underlying mathematical concepts as well as on the practical aspects of the individual algorithms. One segment of the course is devoted to the practical considerations of using many-light methods in the Autodesk Cloud Rendering service.