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Modeling Anisotropic Surface Reflectance with Example-Based Microfacet Synthesis
Jiaping Wang,
Shuang Zhao,
Xin Tong,
John Snyder,
Baining Guo
We present a new technique for the visual modeling of spatiallyvarying
anisotropic reflectance using data captured from a single
view. Reflectance is represented using a microfacet-based BRDF
which tabulates the facets' normal distribution (NDF) as a function
of surface location. Data from a single view provides a 2D slice
of the 4D BRDF at each surface point from which we fit a partial
NDF. The fitted NDF is partial because the single view direction
coupled with the set of light directions covers only a portion of the
"half-angle" hemisphere. We complete the NDF at each point by
applying a novel variant of texture synthesis using similar, overlapping
partial NDFs from other points. Our similarity measure allows
azimuthal rotation of partial NDFs, under the assumption that
reflectance is spatially redundant but the local frame may be arbitrarily
oriented. Our system includes a simple acquisition device
that collects images over a 2D set of light directions by scanning a
linear array of LEDs over a flat sample. Results demonstrate that
our approach preserves spatial and directional BRDF details and
generates a visually compelling match to measured materials.
ACM SIGGRAPH 2008 (to appear)
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Modeling and Rendering Heterogeneous Translucent Materials using Diffusion Equation
Jiaping Wang,
Shuang Zhao,
Xin Tong,
Stephen Lin,
Zhouchen Lin,
Yue Dong,
Baining Guo,
Heung-Yeung Shum
In this paper, we propose techniques for modeling and rendering of heterogeneous translucent materials that enable
acquisition from measured samples, interactive editing of material attributes, and real-time rendering. The materials
are assumed to be optically dense such that multiple scattering can be approximated by a diffusion process described
by the diffusion equation. For modeling heterogeneous materials, we present an algorithm for acquiring material
properties from appearance measurements by solving an inverse diffusion problem. Our modeling algorithm incorporates
a regularizer to handle the ill-conditioned inverse problem, an adjoint method to dramatically reduce the computational
cost, and a hierarchical GPU implementation for further speedup. To display an object with known material properties,
we present an algorithm that performs rendering by solving the diffusion equation with the boundary condition defined
by the given illumination environment. This algorithm is centered around object representation by a
polygrid, a grid with regular connectivity and an irregular shape, which facilitates the
solution of the diffusion equation in arbitrary volumes. Because of the regular connectivity, our rendering algorithm
can be implemented on the GPU for real-time performance. We demonstrate our techniques by capturing materials from
physical samples and performing real-time rendering and editing with these materials.
ACM Transactions on Graphics, Volume 27, Issue 1 (March 2008)
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