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Green Image
Issue No. 04 - July/August (2010 vol. 16)
ISSN: 1077-2626
pp: 548-559
Frida Hernell , Linköping University, Norrköping
Patric Ljung , Siemens Corporate Research, Princeton
Anders Ynnerman , Linköping University, Norrköping
This paper presents a novel technique to efficiently compute illumination for Direct Volume Rendering using a local approximation of ambient occlusion to integrate the intensity of incident light for each voxel. An advantage with this local approach is that fully shadowed regions are avoided, a desirable feature in many applications of volume rendering such as medical visualization. Additional transfer function interactions are also presented, for instance, to highlight specific structures with luminous tissue effects and create an improved context for semitransparent tissues with a separate absorption control for the illumination settings. Multiresolution volume management and GPU-based computation are used to accelerate the calculations and support large data sets. The scheme yields interactive frame rates with an adaptive sampling approach for incrementally refined illumination under arbitrary transfer function changes. The illumination effects can give a better understanding of the shape and density of tissues and so has the potential to increase the diagnostic value of medical volume rendering. Since the proposed method is gradient-free, it is especially beneficial at the borders of clip planes, where gradients are undefined, and for noisy data sets.
Local illumination, volumetric ambient occlusion, volume rendering, medical visualization, emissive tissues, shading, shadowing.

F. Hernell, P. Ljung and A. Ynnerman, "Local Ambient Occlusion in Direct Volume Rendering," in IEEE Transactions on Visualization & Computer Graphics, vol. 16, no. , pp. 548-559, 2009.
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