Direct-to-Indirect Transfer for Cinematic Relighting
Milos Hasan, Fabio Pellacini, Kavita Bala
Proceedings of SIGGRAPH 2006 (SIGGRAPH 2006)
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Abstract:
This paper presents an interactive GPU-based system for cinematic relighting
with multiple-bounce indirect illumination from a fixed view-point. We use a
deep frame-buffer containing a set of view samples, whose indirect illumination
is recomputed from the direct illumination on a large set of gather samples,
distributed around the scene. This direct-to-indirect transfer is a
linear transform which is particularly large, given the size of the view and
gather sets. This makes it hard to precompute, store and multiply with. We
address this problem by representing the transform as a set of sparse matrices
encoded in wavelet space. A hierarchical construction is used to impose a
wavelet basis on the unstructured gather cloud, and an image-based approach is
used to map the sparse matrix computations to the GPU. We precompute the
transfer matrices using a hierarchical algorithm and a variation of photon
mapping in less than three hours on one processor. We achieve high-quality
indirect illumination at 10-20 frames per second for complex scenes with over 2
million polygons, with diffuse and glossy materials, and arbitrary direct
lighting models (expressed using shaders). We compute per-pixel indirect
illumination without the need of irradiance caching or other subsampling
techniques.
Acknowledgments: National Science Foundation (NSF),
Intel Corporation, NVidia for equipment donations.