Kirill Dmitriev

Interactive global illumination using selective photon tracing

We present a method for interactive global illumination computation which is embedded in the framework of Quasi-Monte Carlo photon tracing and density estimation techniques. The method exploits temporal coherence of illumination by tracing photons selectively to the scene regions that require illumination update. Such regions are identified with a high probability by a small number of the pilot photons. Based on the pilot photons which require updating, the remaining photons with similar paths in the scene can be found immediately. This becomes possible due to the periodicity property inherent to the multi-dimensional Halton sequence, which is used to generate photons. If invalid photons cannot all be updated during a single frame, frames are progressively refined in subsequent cycles. The order in which the photons are updated is decided by inexpensive energy- and perception-based criteria whose goal is to minimize the perceivability of outdated illumination. The method buckets all photons on-the-fly in mesh elements and does not require any data structures in the temporal domain, which makes it suitable for interactive rendering of complex scenes. Since mesh-based reconstruction of lighting patterns with high spatial frequencies is inefficient, we use a hybrid approach in which direct illumination and resulting shadows are rendered using graphics hardware.

State of the Art in Global Illumination for Interactive Applications and High-quality Animations

Global illumination algorithms are regarded as computationally intensive. This cost is a practical problem when producing animations or when interactions with complex models are required. Several algorithms have been proposed to address this issue. Roughly, two families of methods can be distinguished. The first one aims at providing interactive feedback for lighting design applications. The second one gives higher priority to the quality of results, and therefore relies on offline computations. Recently, impressive advances have been made in both categories. In this report, we present a survey and classification of the most up‐to‐date of these methods.

Exploiting temporal coherence in global illumination

Producing high quality animations featuring rich object appearance and compelling lighting effects is very time consuming using traditional frame-by-frame rendering systems. In this paper we present a number of global illumination and rendering solutions that exploit temporal coherence in lighting distribution for subsequent frames to improve the computation performance and overall animation quality. Our strategy relies on extending into temporal domain well-known global illumination techniques such as density estimation photon tracing, photon mapping, and bi-directional path tracing, which were originally designed to handle static scenes only.

A CAVE system for interactive modeling of global illumination in car interior

Global illumination dramatically improves realistic appearance of rendered scenes, but usually it is neglected in VR systems due to its high costs. In this work we present an efficient global illumination solution specifically tailored for those CAVE applications, which require an immediate response for dynamic light changes and allow for free motion of the observer, but involve scenes with static geometry. As an application example we choose the car interior modeling under free driving conditions. We illuminate the car using dynamically changing High Dynamic Range (HDR) environment maps and use the Precomputed Radiance Transfer (PRT) method for the global illumination computation. We leverage the PRT method to handle scenes with non-trivial topology represented by complex meshes. Also, we propose a hybrid of PRT and final gathering approach for high-quality rendering of objects with complex Bi-directional Reflectance Distribution Function (BRDF). We use this method for predictive rendering of the navigation LCD panel based on its measured BRDF. Since the global illumination computation leads to HDR images we propose a tone mapping algorithm tailored specifically for the CAVE. We employ head tracking to identify the observed screen region and derive for it proper luminance adaptation conditions, which are then used for tone mapping on all walls in the CAVE. We distribute our global illumination and tone mapping computation on all CPUs and CPUs available in the CAVE, which enables us to achieve interactive performance even for the costly final gathering approach.

Global Illumination for Interactive Applications and High-Quality Animations

One of the main obstacles to the use of global illumination in image synthesis industry is the considerable amount of time needed to compute the lighting for a single image. Until now, this computational cost has prevented its widespread use in interactive design applications as well as in computer animations. Several algorithms have been proposed to address these issues. In this report, we present a much needed survey and classification of the most up-to-date of these methods. Roughly, two families of algorithms can be distinguished. The first one aims at providing interactive feedback for lighting design applications. The second one gives higher priority to the quality of results, and therefore relies on offline computations. Recently, impressive advances have been made in both categories. Indeed, with the steady progress of computing resources and graphics hardware, and the current trend of new algorithms for animated scenes, common use of global illumination seems closer than ever.

Spatio-temporal photon density estimation using bilateral filtering

Photon tracing and density estimation are well established techniques in global illumination computation and rendering of high-quality animation sequences. Using traditional density estimation techniques it is difficult to remove stochastic noise inherent for photon-based methods while avoiding overblurring lighting details. In this paper we investigate the use of bilateral filtering for lighting reconstruction based on the local density of photon hit points. Bilateral filtering is applied in spatio-temporal domain and provides control over the level-of-details in reconstructed lighting. All changes of lighting below this level are treated as stochastic noise and are suppressed. Bilateral filtering proves to be efficient in preserving sharp features in lighting which is in particular important for high-quality caustic reconstruction. Also, flickering between subsequent animation frames is substantially reduced due to extending bilateral filtering into temporal domain

Goniometric Diagram Mapping for Hemisphere

Describing the light intensity over the hemisphere using a goniometric diagram is a common practice in the lighting industry and is prescribed for instance by IESNA (Illuminating Engineering Society of North America) standards. Goniometric diagram species the spatial distribution of the emitted power via a hemispherical surface subdivided by meridians and parallels. Similar tabulated representations are extensively used for complex bidirectional reectance distribution functions (BRDF) that are difcult to approximate with analytical models. We present an approximative bicontinuous mapping from the unit square to a goniometric diagram on the hemisphere. This mapping has low distortion and the error of the approximation is low. The proposed mapping algorithm is obtained as a composition of four mappings. We outline its use for importance sampling of light sources described by goniometric diagrams and for the representation of BRDF. Note: This is a preliminary version of the text that should appear in Eurographics Short Presentations 2003. For a complete version of the text and other details, please, contact the r st author or/and access the Eurographics Digital Library: http://www.eg.org/EG/DL.

Light propagation visualization as a tool for 3D scene analysis in lighting design

Abstract This paper is devoted to a designer tool, which is an extension of particle tracing algorithm for analysis of scenes, artifacts, image ghosts, and ray-tracing mechanism itself. The global illumination problem here is considered at the level of light propagation visualization, which takes into account all cognitive benefits of visual representation. Physically accurate particle tracers randomly generate thousands of rays per second to simulate light propagation in a scene considering light as consisting of photons with a constant energy. The proposed tool utilizes and filters the information of how light photons propagate in the scene. Several examples in the paper demonstrate a practical value of obtained photon tracks for scene analysis.