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Pat Hanrahan - One of the best experts on this subject based on the ideXlab platform.

  • Radiosity and Realistic Image Synthesis
    2016
    Co-Authors: Michael F Cohen, John R Wallace, Pat Hanrahan
    Abstract:

    Introduction: Realistic Image Synthesis, Goals and Limitations. A Short Historical Perspective of Image Synthesis. Radiosity and Finite Element Methods. The Radiosity Algorithm and This Book. Rendering Concepts: Motivation. Basic Optics. Radiometry and Photometry. The Light Field. Reflection Functions. The Rendering Equation. Discretizing the Radiosity Equation: the Radiosity Function. Making Image Synthesis Tractable. The Radiosity Approach. Approximating the Radiosity Across a Surface. Error Metrics. Constant Element Radiosities. Higher Order Basic Functions. Parametric Mapping to a Master Element. Summary. The Form Factor, The Form Factor Integral: the Coefficients of K. The Differential Form Factor. Three Formulations of the Form Factor. Computing the Form Factor. Closed Form Solutions for the Form Factor: Formulae for Simple Shapes. Differential Area to Convex Polygon. General Polygon to Polygon. Numerical Solutions for the Form Factor: Numerical Integration in General. Evaluating the Inner Integral. Full Area to Area Quadrature. Contour Integral Formulation. A Simple Test Environment. Non-Constant Basis Functions. Acceleration Techniques. Radiosity Matrix Solutions: Qualities of the Matrix. Linear System Solution Methods. Relaxation Methods. Dynamic Environments. Parallel Implementations. Domain Subdivision: Error Metrics. Mesh Characteristics and Accuracy. Automatic Meshing Algorithms. Hierarchical and Importance Based Algorithms: Observations About K. Two Level Hierarchy. Multi-Level Hierarchy. Importance Meshing. Hierarchical Basis Functions. Summary of Hierarchical Radiosity Methods. Meshing: Basic Subdivision Techniques. Mesh Template Methods. Decomposition Methods. Mesh Smoothing. Discontinuity Meshing. Topological Data Structures and Operators. Alternatives to Meshing. Rendering: Reconstructing the Radiosity Functions. Interpolation Methods for Rendering. Two-Pass Methods. Incorporating Surface Detail. Mapping Radiosities to Pixel Colours. Colour. Summary. Extensions: Non-Diffuse Light Sources. Directional Reflection. Participating Media. Conclusion and Future Directions.

  • textures and Radiosity controlling emission and reflection with texture maps
    1994
    Co-Authors: Reid Gershbein, Peter Schroder, Pat Hanrahan
    Abstract:

    In this paper we discuss the efficient and accurate incorporation of texture maps into a hierarchical Galerkin Radiosity algorithm. This extension of the standard algorithm allows the use of textures to describe complex reflectance and emittance patterns over surfaces, increasing the realism and complexity of Radiosity images. Previous approaches to the inclusion of textures have either averaged the texture to yield a single color for the Radiosity computations, or exhaustively generated detail elements—possibly as many as one per texture pixel. The former does not capture important lighting effects due to textures, while the latter is too expensive computationally to be practical.To handle texture maps requires a detailed analysis of the underlying operator equation. In particular we decompose the Radiosity equation into two steps: (i) the computation of irradiance on a surface from the radiosities on other surfaces, and (ii) the application of the reflectance operator r to compute radiosities from irradiances. We then describe an algorithm that maintains hierarchical representations of both radiosities and textures. The numerical error involved in using these approximations is quantifiable and a time/error tradeoff is possible. The resulting algorithm allows texture maps to be used in Radiosity computations with very little overhead.

  • partitioning and ordering large Radiosity computations
    1994
    Co-Authors: Seth Teller, Celeste Fowler, Thomas Funkhouser, Pat Hanrahan
    Abstract:

    We describe a system that computes Radiosity solutions for polygonal environments much larger than can be stored in main memory. The solution is stored in and retrieved from a database as the computation proceeds. Our system is based on two ideas: the use of visibility oracles to find source and blocker surfaces potentially visible to a receiving surface; and the use of hierarchical techniques to represent interactions between large surfaces efficiently, and to represent the computed Radiosity solution compactly. Visibility information allows the environment to be partitioned into subsets, each containing all the information necessary to transfer light to a cluster of receiving polygons. Since the largest subset needed for any particular cluster is much smaller than the total size of the environment, these subset computations can be performed in much less memory than can classical or hierarchical Radiosity. The computation is then ordered for further efficiency. Careful ordering of energy transfers minimizes the number of database reads and writes. We report results from large solutions of unfurnished and furnished buildings, and show that our implementation's observed running time scales nearly linearly with both local and global model complexity.

  • wavelet projections for Radiosity
    1994
    Co-Authors: Peter Schroder, Michael F Cohen, Steven J Gortler, Pat Hanrahan
    Abstract:

    One important goal of image synthesis research is to accelerate the process of obtaining realistic images using the Radiosity method. Two important concepts recently introduced are the general framework of projection methods and the hierarchical Radiosity method. Wavelet theory, which explores the space of hierarchical basis functions, offers an elegant framework that unites these two concepts and allows us to more formally understand the hierarchical Radiosity method. Wavelet expansions of the Radiosity kernel have negligible entries in regions where high frequency/fine detail information is not needed. A sparse system remains if these entries are ignored. This is similar to applying a lossy compression scheme to the form factor matrix. The sparseness of the system allows for asymptotically faster Radiosity algorithms by limiting the number of matrix terms that need to be computed. The application of these methods to 3D environments is described in4. Due to space limitations in that paper many of the subtleties of the construction could not be explored there. In this paper we discuss some of the mathematical details of wavelet projections and investigate the application of these methods to the Radiosity kernel of a flatland environment, where many aspect are easier to visualize.

  • a rapid hierarchical Radiosity algorithm for unoccluded environments
    1992
    Co-Authors: Pat Hanrahan, David Salzman
    Abstract:

    This paper presents a linear-time Radiosity algorithm for scenes containing large mutually unoccluded polygonal patches. It subdivides pairs of patches adaptively to build a hierarchical data structure with n elements at the leaves, and it encodes all the light transport between component polygonal elements. Given a required numerical precision, determined by the specified bounds for maximum solid angle F e and minimum area A e , our algorithm reduces the number of form factor calculations and interactions to 0(n) in the worst case and \(\sqrt {O\left( n \right)} \) in the best case. Standard techniques for shooting and gathering can then be used with the data structure. The best previous Radiosity algorithms represented the element-to-element transport interactions with n 2 form factors.

Donald P. Greenberg - One of the best experts on this subject based on the ideXlab platform.

  • bounds and error estimates for Radiosity
    1994
    Co-Authors: Dani Lischinski, Brian Smits, Donald P. Greenberg
    Abstract:

    We present a method for determining a posteriori bounds and estimates for local and total errors in Radiosity solutions. The ability to obtain bounds and estimates for the total error is crucial fro reliably judging the acceptability of a solution. Realistic estimates of the local error improve the efficiency of adaptive Radiosity algorithms, such as hierarchical Radiosity, by indicating where adaptive refinement is necessary.First, we describe a hierarchical Radiosity algorithm that computes conservative lower and upper bounds on the exact Radiosity function, as well as on the approximate solution. These bounds account for the propagation of errors due to interreflections, and provide a conservative upper bound on the error. We also describe a non-conservative version of the same algorithm that is capable of computing tighter bounds, from which more realistic error estimates can be obtained. Finally, we derive an expression for the effect of a particular interaction on the total error. This yields a new error-driven refinement strategy for hierarchical Radiosity, which is shown to be superior to brightness-weighted refinement.

  • a clustering algorithm for Radiosity in complex environments
    1994
    Co-Authors: Brian Smits, James Arvo, Donald P. Greenberg
    Abstract:

    We present an approach for accelerating hierarchical Radiosity by clustering objects. Previous approaches constructed effective hierarchies by subdividing surfaces, but could not exploit a hierarchical grouping on existing surfaces. This limitation resulted in an excessive number of initial links in complex environments. Initial linking is potentially the most expensive portion of hierarchical Radiosity algorithms, and constrains the complexity of the environments that can be simulated. The clustering algorithm presented here operates by estimating energy transfer between collections of objects while maintaining reliable error bounds on each transfer. Two methods of bounding the transfers are employed with different tradeoffs between accuracy and time. In contrast with the O(s2) time and space complexity of the initial linking in previous hierarchical Radiosity algorithms, the new methods have complexities of O(slogs) and O(s) for both time and space. Using these methods we have obtained speedups of two orders of magnitude for environments of moderate complexity while maintaining comparable accuracy.

  • combining hierarchical Radiosity and discontinuity meshing
    1993
    Co-Authors: Dani Lischinski, Filippo Tampieri, Donald P. Greenberg
    Abstract:

    We introduce a new approach for the computation of viewindependent solutions to the diffuse global illumination problem in polyhedral environments. The approach combines ideas from hierarchical Radiosity and discontinuity meshing to yield solutions that are accurate both numerically and visually. First, we describe a modified hierarchical Radiosity algorithm that uses a discontinuitydriven subdivision strategy to achieve better numerical accuracy and faster convergence. Second, we present a new algorithm based on discontinuity meshing that uses the hierarchical solution to reconstruct an object-space approximation to the radiance function that is visually accurate. Our results show significant improvements over both hierarchical Radiosity and discontinuity meshing algorithms. CR Categories and Subject Descriptors: I.3.3—[ Computer Graphics]: Picture/Image Generation; I.3.7—[ Computer Graphics]: Three-Dimensional Graphics and Realism.

  • Discontinuity meshing for accurate Radiosity
    1992
    Co-Authors: Dani Lischinski, Filippo Tampieri, Donald P. Greenberg
    Abstract:

    An algorithm for compactly and accurately capturing the illumination of a diffuse polyhedral environment caused by an area light source is presented. The algorithm constructs a discontinuity mesh that explicitly represents discontinuities in the radiance function as boundaries between mesh elements. A piecewise quadratic interpolant is used to approximate the radiance function, preserving the discontinuities associated with the edges in the mesh. >

Athanasios Tzempelikos - One of the best experts on this subject based on the ideXlab platform.

  • analysis of balance between modeling accuracy and computational speed for a hybrid ray tracing and Radiosity method used in lighting simulation
    2013
    Co-Authors: Yingchieh Chan, Athanasios Tzempelikos
    Abstract:

    A new hybrid ray-tracing and Radiosity method was developed to adopt a balance between computational speed and accuracy when simulating building interior illuminance distributions. The method is able to model spaces with highly specular components, highly diffuse components (i.e., walls, floors, roller shades), as well as components with mixed properties that strongly affect the daylighting performance of the space (i.e., venetian blinds and light-shelves). The specular components are processed with a forward ray-tracing method, while the diffuse components are processed with a Radiosity method. The concept of shining factors is used to separate luminous flux though components with mixed properties, while parameter settings affect both simulation speed and accuracy of results. In this paper, the amount of light rays (tracing resolution) used in the ray-tracing part and the grid size (space resolution) used in the Radiosity part are investigated to analyze the impact of those parameters when predicting work plane illuminance and lighting energy consumption. Use of high numbers of generated rays and high grid density can provide detailed illuminance results. However, the penalties associated with computational time may exceed the accuracy requirements. Recommendations for best settings for different modeling cases are provided so as to balance accuracy versus computational speed. The outcomes of this study can provide useful information for modeling daylighting performance of spaces with specular, diffuse and mixed reflection components such as blinds and light-shelves.

  • a hybrid ray tracing and Radiosity method for calculating radiation transport and illuminance distribution in spaces with venetian blinds
    2012
    Co-Authors: Yingchieh Chan, Athanasios Tzempelikos
    Abstract:

    Abstract This paper presents a hybrid ray-tracing and Radiosity method for processing luminous flux in spaces equipped with horizontal venetian blinds. The method considers both diffuse and specular characteristics of the blinds and aims to establish a balance between computational speed and accuracy. Direct components are treated with ray-tracing techniques employing a shining factor for the blinds to split between specularly and diffusely reflected components. The specular components are traced inside the blind cavity and inside the room while the direct-diffuse components inside the blind cavity are processed in a two-dimensional Radiosity calculation until the final diffuse flux departing the cavity is determined. Diffuse-to-diffuse transmission is considered using a traditional Radiosity method. Each room surface is divided into sub-surfaces and given an initial luminous exitance, after accounting for directly traced portions. Then a three-dimensional Radiosity method is employed for the entire room to compute illuminance distributions on each sub-surface and on the work plane. Comparison between the current model and results obtained with full Radiosity showed that significant errors can be introduced by improper modeling of blind specular components for almost all profile angles and slat angles. An in-depth analysis of the transmission process with different profile angles and shining factors showed the potential of blinds with diffuse characteristics to transmit more light than blinds with highly specular surfaces for certain angles. Further analysis for profile angle close to 45°, showed that for certain commonly used slat angles, a second reflection occurs at the bottom side of the upper slat, redirecting direct light towards the work plane, with serious potential glare consequences. The model contributes to rapid and accurate assessment of illuminance/solar radiation distribution in spaces with venetian blinds and related potential lighting energy savings when electric lighting controls are utilized. Analysis of the number of inter-reflections as a function of profile and slat angles with simultaneous consideration of different reflectances and shining factors is particularly important for providing guidelines and recommendations for venetian blinds optimized design and control.

François X. Sillion - One of the best experts on this subject based on the ideXlab platform.

  • space time hierarchical Radiosity with clustering and higher order wavelets
    2004
    Co-Authors: Cyrille Damez, Nicolas Holzschuch, François X. Sillion
    Abstract:

    We address in this paper the issue of computing diffuse global illumination solutions for animation sequences. The principal difficulties lie in the computational complexity of global illumination, emphasized by the movement of objects and the large number of frames to compute, as well as the potential for creating temporal discontinuities in the illumination, a particularly noticeable artifact. We demonstrate how space-time hierarchical Radiosity, i.e. the application to the time dimension of a hierarchical decomposition algorithm, can be effectively used to obtain smooth animations: first by proposing the integration of spatial clustering in a space-time hierarchy; second, by using a higher-order wavelet basis adapted for the temporal dimension. The resulting algorithm is capable of creating time-dependent Radiosity solutions efficiently.

  • An Efficient Instantiation Algorithm for Simulating Radiant Energy Transfer in Plant Models
    2003
    Co-Authors: Cyril Soler, François X. Sillion, Frédéric Blaise, Philippe De Reffye
    Abstract:

    We describe a complete lighting simulation system tailored for the difficult case of vegetation scenes. Our algorithm is based on hierarchical instantiation for Radiosity and precise phase function modeling. It allows efficient calculations both in terms of computation and memory resources. We provide an in-depth description and study of the instantiation-based Radiosity technique and we address the problems related to generating and managing phase functions of plant structures, as needed by the instantiation process. We present results demonstrating the high performance of the hierarchical instantiation algorithm and we describe two examples of applications: rendering of large vegetation scenes and plant growth simulation. Other applications of our system range from landscape simulation to agronomical and agricultural studies, and to the design of virtual plants responding to their environment.

  • hierarchical instantiation for Radiosity
    2000
    Co-Authors: Cyril Soler, François X. Sillion
    Abstract:

    We present the concept of hierarchical instantiation for Radiosity. This new method enables an efficient, yet accurate determination of the illumination in very large scenes, where similar objects are replaced by instances of the same element. Instances are equipped with suitable radiative properties and are used to replace large amounts of geometry at multiple levels of the scene hierarchy. In essence, our algorithm replaces a single very large hierarchical Radiosity problem by a collection of hierarchical Radiosity problems within small sets of objects at a time, at several hierarchical levels. We prove the applicability of our method on architectural scenes with replicated geometry. However we reach the best time and memory gains on plant models thanks to the high degree of self-similarity in such kinds of scenes. This allows us to compute lighting simulations on scenes including a very large number of polygons in a short time on machines with limited memory.

  • accurate computation of the Radiosity gradient for constant and linear emitters
    1995
    Co-Authors: Nicolas Holzschuch, François X. Sillion
    Abstract:

    Controlling the error incurred in a Radiosity calculation is one of the most challenging issues remaining in global illumination research. In this paper we propose a new method to compute the value and the gradient of the Radiosity function at any point of a receiver, with arbitrary precision. The knowledge of the gradient provides fundamental informations on the Radiosity function and its behaviour. It can specially be used to control the consistency of the discretisation assumptions.

  • clustering and volume scattering for hierarchical Radiosity calculations
    1995
    Co-Authors: François X. Sillion
    Abstract:

    This paper introduces a new approach to hierarchical Radiosity computation, making it practical for the simulation of energy exchanges in very complex environments. Results indicate that the new formulation allows the effective simulation of environments of significant complexity, containing several thousands of surfaces or volumes.

Jaakko Lehtinen - One of the best experts on this subject based on the ideXlab platform.

  • sequential monte carlo instant Radiosity
    2017
    Co-Authors: Peter Hedman, Tero Karras, Jaakko Lehtinen
    Abstract:

    Instant Radiosity and its derivatives are interactive methods for efficiently estimating global (indirect) illumination. They represent the last indirect bounce of illumination before the camera as the composite radiance field emitted by a set of virtual point light sources (VPLs). In complex scenes, current algorithms suffer from a difficult combination of two issues: it remains a challenge to distribute VPLs in a manner that simultaneously gives a high-quality indirect illumination solution for each frame, and to do so in a temporally coherent manner. We address both issues by building, and maintaining over time, an adaptive and temporally coherent distribution of VPLs in locations where they bring indirect light to the image. We introduce a novel heuristic sampling method that strives to only move as few of the VPLs between frames as possible. The result is, to the best of our knowledge, the first interactive global illumination algorithm that works in complex, highly-occluded scenes, suffers little from temporal flickering, supports moving cameras and light sources, and is output-sensitive in the sense that it places VPLs in locations that matter most to the final result.

  • sequential monte carlo instant Radiosity
    2016
    Co-Authors: Peter Hedman, Tero Karras, Jaakko Lehtinen
    Abstract:

    Instant Radiosity and its derivatives are interactive methods for efficiently estimating global (indirect) illumination. They represent the last indirect bounce of illumination before the camera as the composite radiance field emitted by a set of virtual point light sources (VPLs). In complex scenes, current algorithms suffer from a difficult combination of two issues: it remains a challenge to distribute VPLs in a manner that simultaneously gives a high-quality indirect illumination solution for each frame, and does so in a temporally coherent manner. We address both issues by building, and maintaining over time, an adaptive and temporally coherent distribution of VPLs in locations where they bring indirect light to the image. We introduce a novel heuristic sampling method that strives to only move as few of the VPLs between frames as possible. The result is, to the best of our knowledge, the first interactive global illumination algorithm that works in complex, highly-occluded scenes, suffers little from temporal flickering, supports moving cameras and light sources, and is output-sensitive in the sense that it places VPLs in locations that matter most to the final result.