IEEE SciVis 2013 Honorable Mention Award
IEEE Transactions on Visualization and Computer Graphics, 19(12): 2936-2945, 2013.
M. Ament, F. Sadlo
VISUS, University of Stuttgart, Germany.
This work was partially funded by Deutsche Forschungsgemeinschaft (DFG) under grant WE 2836/2-1 ("Astrographik") and the Cluster of Excellence in Simulation Technology (EXC 310/1). The authors thank the U.S. National Library of Medicine, OsiriX, Dr. John Blondin, and Prof. Ulrich Rist for providing data sets.
We present ambient scattering as a preintegration method for scattering on mesoscopic scales in direct volume rendering. Far-range scattering effects usually provide negligible contributions to a given location due to the exponential attenuation with increasing distance. This motivates our approach to preintegrating multiple scattering within a finite spherical region around any given sample point. To this end, we solve the full light transport with a Monte-Carlo simulation within a set of spherical regions, where each region may have different material parameters regarding anisotropy and extinction. This precomputation is independent of the data set and the transfer function, and results in a small preintegration table. During rendering, the look-up table is accessed for each ray sample point with respect to the viewing direction, phase function, and material properties in the spherical neighborhood of the sample. Our rendering technique is efficient and versatile because it readily fits in existing ray marching algorithms and can be combined with local illumination and volumetric ambient occlusion. It provides interactive volumetric scattering and soft shadows, with interactive control of the transfer function, anisotropy parameter of the phase function, lighting conditions, and viewpoint. A GPU implementation demonstrates the benefits of ambient scattering for the visualization of different types of data sets, with respect to spatial perception, high-quality illumination, translucency, and rendering speed.
Comparison with Path Tracing (Visible Human)
Comparison with Path Tracing (Supernova)
This C++ program implements a class AVSTable2D that loads one 2D slice of the 3D preintegration table from disk into memory. The main routine of the program loads all slice files of a 3D table and plots the 2D radiance distribution of each slice into separate image files (.ppm file format). Please read the README file in the zip archive for more details.
Each of the following 3D tables samples the parameter ranges ?? in [0,??], ?? in [0,20], and g in [-0.9,0.9] uniformly with a resolution of 256 x 256 x 19 data points. The albedo of each 3D table remains constant. We provide table data for albedo values ranging from 0.1 to 0.9. An albedo value of 0.0 corresponds to the emission-absorption model without scattering, whereas a value of 1.0 is non-physical.
Download albedo 0.9 (4.4 MB) [This table was used in the paper]