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Exploiting Temporal Coherence for Pre-computation Based Rendering

Overbeck, Ryan S.

Precomputed radiance transfer (PRT) generates impressive images with complex illumination, materials and shadows with real-time interactivity. These methods separate the sceneäó»s static and dynamic components allowing the static portion to be computed as a preprocess. In this work, we hold geometry static and allow either the lighting or BRDF to be dynamic. To achieve real-time performance, both static and dynamic components are compressed by exploiting spatial and angular coherence. Temporal coherence of the dynamic component from frame to frame is an important, but unexplored additional form of coherence. In this thesis, we explore temporal coherence of two forms of all-frequency PRT: BRDF material editing and lighting design. We develop incremental methods for approximating the differences in the dynamic component between consecutive frames. For BRDF editing, we find that a pure incremental approach allows quick convergence to an exact solution with smooth real-time response. For relighting, we observe vastly differing degrees of temporal coherence accross levels of the lightingäó»s wavelet hierarchy. To address this, we develop an algorithm that treats each level separately, adapting to available coherence. The proposed methods are orthogonal to other forms of coherence, and can be added to almost any PRT algorithm with minimal implementation, computation, or memory overhead. We demonstrate our technique within existing codes for nonlinear wavelet approximation, changing view with BRDF factorization, and clustered PCA. Exploiting temporal coherence of dynamic lighting yields a 3×-4ׄ performance improvement, e.g., all-frequency effects are achieved with 30 wavelet coefficients, about the same as low-frequency spherical harmonic methods. Distinctly, our algorithm smoothly converges to the exact result within a few frames of the lighting becoming static.

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Academic Units
Computer Science
Publisher
Department of Computer Science, Columbia University
Series
Columbia University Computer Science Technical Reports, CUCS-025-06
Published Here
April 27, 2011