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Historygrams: Enabling Interactive Global Illumination in Direct Volume Rendering using Photon Mapping
Dec. 2012 (vol. 18 no. 12)
pp. 2364-2371
D. Jonsson, Linkoping Univ., Linkoping, Sweden
J. Kronander, Linkoping Univ., Linkoping, Sweden
T. Ropinski, Linkoping Univ., Linkoping, Sweden
A. Ynnerman, Linkoping Univ., Linkoping, Sweden
In this paper, we enable interactive volumetric global illumination by extending photon mapping techniques to handle interactive transfer function (TF) and material editing in the context of volume rendering. We propose novel algorithms and data structures for finding and evaluating parts of a scene affected by these parameter changes, and thus support efficient updates of the photon map. In direct volume rendering (DVR) the ability to explore volume data using parameter changes, such as editable TFs, is of key importance. Advanced global illumination techniques are in most cases computationally too expensive, as they prevent the desired interactivity. Our technique decreases the amount of computation caused by parameter changes, by introducing Historygrams which allow us to efficiently reuse previously computed photon media interactions. Along the viewing rays, we utilize properties of the light transport equations to subdivide a view-ray into segments and independently update them when invalid. Unlike segments of a view-ray, photon scattering events within the volumetric medium needs to be sequentially updated. Using our Historygram approach, we can identify the first invalid photon interaction caused by a property change, and thus reuse all valid photon interactions. Combining these two novel concepts, supports interactive editing of parameters when using volumetric photon mapping in the context of DVR. As a consequence, we can handle arbitrarily shaped and positioned light sources, arbitrary phase functions, bidirectional reflectance distribution functions and multiple scattering which has previously not been possible in interactive DVR.
Index Terms:
rendering (computer graphics),interactive systems,lighting,bidirectional reflectance distribution functions,historygram approach,direct volume rendering,photon mapping techniques,interactive volumetric global illumination,interactive transfer function,TF,material editing,DVR,advanced global illumination techniques,parameter change,photon media interactions,light transport equations,view-ray,photon scattering events,property change,light sources,arbitrary phase functions,Photonics,Lighting,Rendering (computer graphics),Scattering,Volume measurement,participating media,Volume rendering,photon mapping,global illumination
Citation:
D. Jonsson, J. Kronander, T. Ropinski, A. Ynnerman, "Historygrams: Enabling Interactive Global Illumination in Direct Volume Rendering using Photon Mapping," IEEE Transactions on Visualization and Computer Graphics, vol. 18, no. 12, pp. 2364-2371, Dec. 2012, doi:10.1109/TVCG.2012.232
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