Vincent Pegoraro

A directional occlusion shading model for interactive direct volume rendering

Volumetric rendering is widely used to examine 3D scalar fields from CT/MRI scanners and numerical simulation datasets. One key aspect of volumetric rendering is the ability to provide perceptual cues to aid in understanding structure contained in the data. While shading models that reproduce natural lighting conditions have been shown to better convey depth information and spatial relationships, they traditionally require considerable (pre)computation. In this paper, a shading model for interactive direct volume rendering is proposed that provides perceptual cues similar to those of ambient occlusion, for both solid and transparent surface‐like features. An image space occlusion factor is derived from the radiative transport equation based on a specialized phase function. The method does not rely on any precomputation and thus allows for interactive explorations of volumetric data sets via on‐the‐fly editing of the shading model parameters or (multi‐dimensional) transfer functions while modifications to the volume via clipping planes are incorporated into the resulting occlusion‐based shading.

An Analytical Solution to Single Scattering in Homogeneous Participating Media

Despite their numerous applications, efficiently rendering participating media remains a challenging task due to the intricacy of the radiative transport equation. As they provide a generic means of solving a wide variety of problems, numerical methods are most often used to solve the air‐light integral even under simplifying assumptions. In this paper, we present a novel analytical approach to single scattering from isotropic point light sources in homogeneous media. We derive the first closed‐form solution to the air‐light integral in isotropic media and extend this formulation to anisotropic phase functions. The technique relies neither on pre‐computation nor on storage, and we provide a practical implementation allowing for an explicit control on the accuracy of the solutions. Finally, we demonstrate its quantitative and qualitative benefits over both previous numerical and analytical approaches.

Physically-based realistic fire rendering

Accurately rendering fires is a challenging problem due to the various subtle ways in which the electromagnetic waves interact with this complex participating medium. We present a new method for physically-based rendering of flames from detailed simulations of flame dynamics which accounts for their unique characteristics. Instead of relying on ad-hoc models, we build on fundamental molecular physics to compute the spectrally dependent absorption, emission and scattering properties of the various chemical compounds found in the fire. Combined with a model of the refractive process, and with tone-mapping techniques simulating the visual adaptation of a human observer, we are able to generate highly realistic renderings of various types of flames, including colorful flames containing chemical species with very characteristic spectral properties.

Depth of field effects for interactive direct volume rendering

In this paper, a method for interactive direct volume rendering is proposed for computing depth of field effects, which previously were shown to aid observers in depth and size perception of synthetically generated images. The presented technique extends those benefits to volume rendering visualizations of 3D scalar fields from CT/MRI scanners or numerical simulations. It is based on incremental filtering and as such does not depend on any pre‐computation, thus allowing interactive explorations of volumetric data sets via on‐the‐fly editing of the shading model parameters or (multi‐dimensional) transfer functions.

Physically-Based Interactive Flow Visualization Based on Schlieren and Interferometry Experimental Techniques

Understanding fluid flow is a difficult problem and of increasing importance as computational fluid dynamics (CFD) produces an abundance of simulation data. Experimental flow analysis has employed techniques such as shadowgraph, interferometry, and schlieren imaging for centuries, which allow empirical observation of inhomogeneous flows. Shadowgraphs provide an intuitive way of looking at small changes in flow dynamics through caustic effects while schlieren cutoffs introduce an intensity gradation for observing large scale directional changes in the flow. Interferometry tracks changes in phase-shift resulting in bands appearing. The combination of these shading effects provides an informative global analysis of overall fluid flow. Computational solutions for these methods have proven too complex until recently due to the fundamental physical interaction of light refracting through the flow field. In this paper, we introduce a novel method to simulate the refraction of light to generate synthetic shadowgraph, schlieren and interferometry images of time-varying scalar fields derived from computational fluid dynamics data. Our method computes physically accurate schlieren and shadowgraph images at interactive rates by utilizing a combination of GPGPU programming, acceleration methods, and data-dependent probabilistic schlieren cutoffs. Applications of our method to multifield data and custom application-dependent color filter creation are explored. Results comparing this method to previous schlieren approximations are finally presented.

A closed-form solution to single scattering for general phase functions and light distributions

Due to the intricate nature of the equation governing light transport in participating media, accurately and efficiently simulating radiative energy transfer remains very challenging in spite of its broad range of applications. As an alternative to traditional numerical estimation methods such as ray‐marching and volume‐slicing, a few analytical approaches to solving single scattering have been proposed but current techniques are limited to the assumption of isotropy, rely on simplifying approximations and/or require substantial numerical precomputation and storage. In this paper, we present the very first closed‐form solution to the air‐light integral in homogeneous media for general 1‐D anisotropic phase functions and punctual light sources. By addressing an open problem in the overall light transport literature, this novel theoretical result enables the analytical computation of exact solutions to complex scattering phenomena while achieving semi‐interactive performance on graphics hardware for several common scattering modes.

Towards interactive global illumination effects via sequential Monte Carlo adaptation

This paper presents a novel method that effectively combines both control variates and importance sampling in a sequential Monte Carlo context while handling general single-bounce global illumination effects. The radiance estimates computed during the rendering process are cached in an adaptive per-pixel structure that defines dynamic predicate functions for both variance reduction techniques and guarantees well-behaved PDFs, yielding continually increasing efficiencies thanks to a marginal computational overhead. While remaining unbiased, the technique is effective within a single pass as both estimation and caching are done online, exploiting the coherency in illumination while being independent of the actual scene representation. The method is relatively easy to implement and to tune via a single parameter, and we demonstrate its practical benefits with important gains in convergence rate and applications to both off-line and progressive interactive rendering.

Sequential monte carlo integration in low-anisotropy participating media

This paper presents a novel method that effectively combines both control variates and importance sampling in a sequential Monte Carlo context. The radiance estimates computed during the rendering process are cached in a 5D adaptive hierarchical structure that defines dynamic predicate functions for both variance reduction techniques and guarantees well‐behaved PDFs, yielding continually increasing efficiencies thanks to a marginal computational overhead. While remaining unbiased, the technique is effective within a single pass as both estimation and caching are done online, exploiting the coherency in illumination while being independent of the actual scene representation. The method is relatively easy to implement and to tune via a single parameter, and we demonstrate its practical benefits with important gains in convergence rate and competitive results with state of the art techniques.

An Open Modular Architecture for Effective Integration of Virtual Worlds in the Web

The Web and virtual worlds are currently crossing their ways, and although there are some efforts made to integrate them into each other, those typically rely on technologies that are rather esoteric to most web-developers. In this paper, we present a new open architecture that combines several emerging and established technologies to provide convenient tools for developing virtual worlds in the Web. These technologies are easy to learn and understand by the web community and allow for quick prototyping. Overall the modular architecture allows virtual worlds to be developed more quickly and more widely deployed.

On the Evaluation of the Complex-Valued Exponential Integral

Abstract Although its applications span a broad scope of scientific fields ranging from applied physics to computer graphics, the exponential integral is a nonelementary special function available in specialized software packages but not in standard libraries, consequently requiring custom implementations on most platforms. In this paper, we provide a concise and comprehensive description of how to evaluate the complex-valued exponential integral. We first introduce some theoretical background on the main characteristics of the function, and outline available third-party proprietary implementations. We then provide an analysis of the various known representations of the function and present an effective algorithm allowing the computation of results within a desired accuracy, together with the corresponding pseudocode in order to facilitate portability onto various systems. An application to the calculation of the closed-form solution to single light scattering in homogeneous participating media illustrates the practical benefits of the provided implementation with the hope that, in the long term, the latter will contribute to standardizing the availability of the complex-valued exponential integral on graphics platforms.