Abstract
The field of volume visualization has undergone rapid development during the past years, both due to advances in suitable computing hardware and due to the increasing availability of large volume datasets. Recent work has focused on increasing the visual realism in Direct Volume Rendering (DVR) by integrating a number of visually plausible but often effect-specific rendering techniques, for instance modeling of light occlusion and depth of field. Besides yielding more attractive renderings, especially the more realistic lighting has a positive effect on perceptual tasks. Although these new rendering techniques yield impressive results, they exhibit limitations in terms of their exibility and their performance. Monte Carlo ray tracing (MCRT), coupled with physically based light transport, is the de-facto standard for synthesizing highly realistic images in the graphics domain, although usually not from volumetric data. Due to the stochastic sampling of MCRT algorithms, numerous effects can be achieved in a relatively straight-forward fashion. For this reason, we have developed a practical framework that applies MCRT techniques also to direct volume rendering (DVR). With this work, we demonstrate that a host of realistic effects, including physically based lighting, can be simulated in a generic and flexible fashion, leading to interactive DVR with improved realism. In the hope that this improved approach to DVR will see more use in practice, we have made available our framework under a permissive open source license.
Highlights
Realistic illumination in volume visualization plays a central role in 3D shape perception
Our contributions are the following: N We demonstrate that Monte Carlo ray tracing (MCRT) is an appealing approach to Direct Volume Rendering (DVR), allowing a host of effects and flexible lighting schemes, and that it can be run efficiently on commodity graphics hardware using CUDA, with the necessary performance optimizations
Exposure Render, a complete interactive DVR framework, which has been made publicly available through a Google Code project: http://code.google.com/p/exposurerender/
Summary
Realistic illumination in volume visualization plays a central role in 3D shape perception. The user study performed by Lindemann et al [1], in which the effectiveness of seven state of the art DVR techniques is measured, clearly showed that global illumination models help in assessing depth and size in images. Recent years have seen a great deal of research towards enhancing interactive Direct Volume Rendering (DVR) approaches with more realistic illumination, for example ambient occlusion [3], shadows [4,5], realistic scattering [6,7] and global illumination [8]. In contrast to many of the existing approximations, Monte Carlo ray tracing (MCRT), combined with physically based light transport, is able to simulate real-world light interaction without compromising accuracy of light transport computations, resulting in more realistic images. This distinction is discussed in more detail in the Related Work section
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