Structured Penumbral Irradiance Computation

George Drettakis 1, * Eugene Fiume 2
* Corresponding author
1 iMAGIS - Models, Algorithms and Geometry for Computer Generated Image Graphics
GRAVIR - IMAG - Graphisme, Vision et Robotique, Inria Grenoble - Rhône-Alpes
Abstract : A definitive understanding of irradiance behavior in penumbral regions has been hard to come by, mainly due to the computational expense of determining the visible parts of an area light source. Consequently, sampling strategies have been mostly ad hoc, and evaluation of the resulting approximations has been difficult. In this paper, the structure of penumbral irra- diance is investigated empirically and numerically. This study has been made feasible by the use of the discontinuity mesh and the backprojection, an efficient data structure representing vis- ibility in regions of partial occlusion. Regions of penumbrae in which irradiance varies non-monotonically are characterized empirically, and numerical tests are performed to determine the frequency of their occurrence. This study inspired the develop- ment of two algorithms for the construction of interpolating approximations to irradiance: one algorithm reduces the num- ber of edges in the mesh defining the interpolant domain, and the other algorithm chooses among linear, quadratic, and mixed interpolants based on irradiance monotonicity. Results from numerical tests and images are presented that demonstrate good performance of the new algorithms for various realistic test con- figurations.
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George Drettakis, Eugene Fiume. Structured Penumbral Irradiance Computation. IEEE Transactions on Visualization and Computer Graphics, Institute of Electrical and Electronics Engineers, 1996, 2 (4). ⟨inria-00509993⟩

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