Global Illumination Simulation Research Articles

Illumination-aware group portrait compositor.

We present a novel compositing framework for full-length human figures that maintains their surface details and appends the localized nature of light and shadow, thereby synthesizing composite results with high visual coherence. The framework is extended from the compositing pipeline proposed in our previous study so that it deploys five stages for photometric information estimation, as well as for 3D reconstruction, global illumination simulation, lighting transfer, and compositing. Based on the interpretation that a sense of coexistence can be achieved through visual coherence, we demonstrate that the proposed framework functions properly as a group portrait compositor. The composite results that the proposed framework composed the images separately rendered 3D human models compared favorably with the results which rendered multiple avatars together. Based on this empirical evaluation, the proposed framework is expected as a new means of fostering a sense of coexistence in remote societies and of efficiently generating highly photorealistic cyberworlds.

Guided Visibility Sampling++

Visibility computation is a common problem in the field of computer graphics. Examples include occlusion culling, where parts of the scene are culled away, or global illumination simulations, which are based on the mutual visibility of pairs of points to calculate lighting. In this paper, an aggressive from-region visibility technique called Guided Visibility Sampling++ (GVS++) is presented. The proposed technique improves the Guided Visibility Sampling algorithm through improved sampling strategies, thus achieving low error rates on various scenes, and being over four orders of magnitude faster than the original CPU-based Guided Visibility Sampling implementation. We present sampling strategies that adaptively compute sample locations and use ray casting to determine a set of triangles visible from a flat or volumetric rectangular region in space. This set is called a potentially visible set (PVS). Based on initial random sampling, subsequent exploration phases progressively grow an intermediate solution. A termination criterion is used to terminate the PVS search. A modern implementation using the Vulkan graphics API and RTX ray tracing is discussed. Furthermore, we show optimizations that allow for an implementation that is over 20 times faster than a naive implementation.

Preserving Shadow Silhouettes in Illumination‐Driven Mesh Reduction

AbstractA main challenge for today's renderers is the ever‐growing size of 3D scenes, exceeding the capacity of typically available main memory. This especially holds true for graphics processing units (GPUs) which could otherwise be used to greatly reduce rendering time. A lot of the memory is spent on detailed geometry with mostly imperceptible influence on the final image, even in a global illumination context. Illumination‐driven mesh reduction, a Monte Carlo–based global illumination simulation, steers its mesh reduction towards areas with low visible contribution. While this works well for preserving high‐energy light paths such as caustics, it does have problems: First, objects casting shadows while not being visible themselves are not preserved, resulting in highly inaccurate shadows. Secondly, non‐transparent objects lack proper reduction guidance since there is no importance gradient on their backside, resulting in visible over‐simplification. We present a solution to these problems by extending illumination‐driven mesh reduction with occluder information, focusing on their silhouettes as well as combining it with commonly used error quadrics to preserve geometric features. Additionally, we demonstrate that the combined algorithm still supports iterative refinement of initially reduced geometry, resulting in an image visually similar to an unreduced rendering and enabling out‐of‐core operation.

An efficient mulithreading algorithm for the simulation of global illumination

The calculation of global illumination taking into account not only the direct light but also all its possible reflections is an important part of the synthesis of realistic images. The simulation of global illumination requires a lot of computational resources. The performance of modern computers directly depends on the number of cores, which allow one to use tens of parallel computation threads. The paper is devoted to the effective use of multicore computers for simulating the global illumination. The computation results are represented in a uniform illumination map. The proposed algorithm dynamically creates additional threads for the critical branches of the computation process or processing of results. As a result, the uniform load of computation threads as achieved, and the physical and virtual cores are fully loaded.

Quantizing Intersections Using Compact Voxels

AbstractEfficient intersection queries are important for ray tracing. However, building and maintaining the acceleration structures is demanding, especially for fully dynamic scenes. In this paper, we propose a quantized intersection framework based on compact voxels to quantize the intersection as an approximation. With high‐resolution voxels, the scene geometry can be well represented, which enables more accurate simulation of global illumination, such as detailed glossy reflections. In terms of memory usage in our graphics processing unit implementation, voxels are binarized and compactly encoded in a few 2D textures. We evaluate the rendering quality at various voxel resolutions. Empirically, high‐fidelity rendering can be achieved at the voxel resolution of 1 K3 or above, which produces images very similar to those of ray tracing. Moreover, we demonstrate the feasibility of our framework for various illumination effects with several applications, including first‐bounce indirect illumination, glossy refraction, path tracing, direct illumination, and ambient occlusion.

A radiative transfer framework for rendering materials with anisotropic structure

The radiative transfer framework that underlies all current rendering of volumes is limited to scattering media whose properties are invariant to rotation. Many systems allow for "anisotropic scattering," in the sense that scattered intensity depends on the scattering angle, but the standard equation assumes that the structure of the medium is isotropic. This limitation impedes physics-based rendering of volume models of cloth, hair, skin, and other important volumetric or translucent materials that do have anisotropic structure. This paper presents an end-to-end formulation of physics-based volume rendering of anisotropic scattering structures, allowing these materials to become full participants in global illumination simulations. We begin with a generalized radiative transfer equation, derived from scattering by oriented non-spherical particles. Within this framework, we propose a new volume scattering model analogous to the well-known family of microfacet surface reflection models; we derive an anisotropic diffusion approximation, including the weak form required for finite element solution and a way to compute the diffusion matrix from the parameters of the scattering model; and we also derive a new anisotropic dipole BSSRDF for anisotropic translucent materials. We demonstrate results from Monte Carlo, finite element, and dipole simulations. All these contributions are readily implemented in existing rendering systems for volumes and translucent materials, and they all reduce to the standard practice in the isotropic case.

Global Illumination Compensation for Spatially Augmented Reality

AbstractWhen projectors are used to display images on complex, non‐planar surface geometry, indirect illumination between the surfaces will disrupt the final appearance of this imagery, generally increasing brightness, decreasing contrast, and washing out colors. In this paper we predict through global illumination simulation this unintentional indirect component and solve for the optimal compensated projection imagery that will minimize the difference between the desired imagery and the actual total illumination in the resulting physical scene. Our method makes use of quadratic programming to minimize this error within the constraints of the physical system, namely, that negative light is physically impossible. We demonstrate our compensation optimization in both computer simulation and physical validation within a table‐top spatially augmented reality system. We present an application of these results for visualization of interior architectural illumination. To facilitate interactive modifications to the scene geometry and desired appearance, our system is accelerated with a CUDA implementation of the QP optimization method.

Imperfect shadow maps for efficient computation of indirect illumination

We present a method for interactive computation of indirect illumination in large and fully dynamic scenes based on approximate visibility queries. While the high-frequency nature of direct lighting requires accurate visibility, indirect illumination mostly consists of smooth gradations, which tend to mask errors due to incorrect visibility. We exploit this by approximating visibility for indirect illumination with imperfect shadow maps ---low-resolution shadow maps rendered from a crude point-based representation of the scene. These are used in conjunction with a global illumination algorithm based on virtual point lights enabling indirect illumination of dynamic scenes at real-time frame rates. We demonstrate that imperfect shadow maps are a valid approximation to visibility, which makes the simulation of global illumination an order of magnitude faster than using accurate visibility.

Progressive radiosity method on clusters using a new clipping algorithm

Global illumination simulation is highly critical for realistic image synthesis; without it, the rendered images look flat and synthetic. The main problem is that the simulation for large scenes is a high time-consuming process. In this paper, we present a uniform partitioning method in order to split the scene domain into a set of disjoint subspaces which are distributed among the processors of a distributed memory system. Since polygons partially inside several subspaces have to be clipped, we have developed a new clipping algorithm to manage this situation. Memory and communication requirements have been minimised in the parallel implementation. Finally, in order to evaluate the proposed method, we have used a progressive radiosity algorithm, running on two different PC clusters with modern processors and network technologies as a testbed. Good results in terms of speedup have been obtained.

Advanced Radiance Estimation For Photon Map Global Illumination

We present a new method to compute radiance in photon map based global illumination simulation for polygonal scenes with general bidirectional scattering distribution functions (BSDFs). Our new radiance estimation uses the actual geometry in the neighborhood of the illuminated point, and does not assume that the nearest neighbor photons lie in the same plane as the point, nor that they are distributed in a circular area around that point. This allows us to achieve accurate indirect illumination by direct visualization of the photon map — which is especially important for the simulation of caustics (LS+DS*E paths) — even in the vicinity of edges and corners of objects, and on surfaces with differently oriented small geometric details.

Validating acoustical simulations in the Bell Labs Box

Researchers at Cornell University constructed a simple real-world scene, the Cornell Box, in which they carefully measured the lighting, geometry, and reflectance properties of every surface and duplicated it in a 3D computer graphics model. Using this simple and controlled experimental setup, they were able to make meaningful comparisons between global illumination simulations and photographs of the scene and provide explanations for the differences. Motivated by the Cornell Box's success, we've built a simple experimental setup for validating sound propagation simulations. Our setup, the Bell Labs Box, comprises a simple configuration of planar surfaces with a speaker and a microphone. Although the room's basic configuration is a simple six-sided box, we constructed it with reconfigurable panels that we can insert or remove to create various interesting geometries, including ones with diffracting panels.

Validation of Global Illumination Simulations through CCD Camera Measurements

Validation of Global Illumination Simulations through CCD Camera Measurements

Adaptive radiosity textures for bidirectional ray tracing

We present a rendering method designed to provide accurate, general simulation of global illumination for realistic image synthesis. Separating surface interaction into diffuse plus specular, we compute the specular component on the fly, as in ray tracing, and store the diffuse component (the radiosity) for later-reuse, similar to a radiosity algorithm. Radiosities are stored in adaptive radiosity textures (rexes ) 1 that record the pattern of light and shadow on every diffuse surface in the scene. They adaptively subdivide themselves to the appropriate level of detail for the picture being made, resolving sharp shadow edges automatically.We use a three-pass, bidirectional ray tracing algorithm that traces rays from both the lights and the eye. The "size pass" records visibility information on diffuse surfaces; the "light pass" progressively traces rays from lights and bright surfaces to deposit photons on diffuse surfaces to construct the radiosity textures; and the "eye pass" traces rays from the eye, collecting light from diffuse surfaces to make a picture.

Radiosity redistribution for dynamic environments

The radiosity algorithm is extended to dynamic environments, providing global-illumination simulations to scenes that are modified interactively. The illumination effects introduced by a change in position, shape, or attributes of any object in the scene are computed very rapidly by redistributing the energy already exchanged between objects. Corrections are made by shooting positive and negative energy, accounting for increased illumination and the creation of shadows. Object coherence is used to minimize computation, and progressive-refinement techniques are used to accelerate convergence. The extended algorithm yields excellent approximations to the exact solutions at interactive speeds. >