Motivation. Motivation

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1 Preserving Preserving Realism Realism in in real-time real-time Rendering Rendering of of Bidirectional Bidirectional Texture Texture Functions Functions Reinhard Klein Bonn University Computer Graphics Group Motivation Hiqh-quality rendering in real-time University of Bonn Computer Graphics Group Müller, Reinhard Klein 1

Reinhard Klein Bonn University Computer Graphics Group Motivation Hiqh-quality

2 Motivation Current real-time applications: triangular models simple materials Textures Bump Mapping Displacement Mapping University of Bonn Computer Graphics Group Müller, Reinhard Klein Motivation Our approach more accurate material representation Real-time rendering University of Bonn Computer Graphics Group Müller, Reinhard Klein 2

Group Müller, Reinhard Klein Motivation Our approach more accurate material

3 Problem Description Real-world materials: complex reflectance behavior (pointwise BRDF) mesostructure with highly complicated self- occlusion, interreflection and self-shadowing shadowing changing perceived normal Previous Work BTF representation by Dana BTF( x, l, v) = BTF( x, y, θ, φ, θ, φ ) l l v v

interreflection and self-shadowing shadowing changing perceived normal

4 Previous Work Efficient Rendering of Spatial Bi-directional Reflectance Distribution Functions McAllister, Lastra, Heidrich,, Graphics Hardware 2002 BTF( x, l, v) ρ + ρ L l, v dx, sxi,, xi, i ( ) C 0 0 x l i x Li( l, v) = ( v x, v y, v z) 0 Cy 0 l i y 0 0 C l zi z N Previous Work Efficient Rendering of Spatial Bi-directional Reflectance Distribution Functions McAllister, Lastra, Heidrich,, Graphics Hardware 2002 Rendering in real-time Good Good results for simple materials View-dependent effects require many lobes Insufficient for materials with high depth variation

2002 Rendering in real-time Good Good results for simple materials View-dependent effects require many lobes Insufficient for materials with

5 Previous Work Efficient Cloth Modeling and Rendering Daubert, Lensch, Heidrich,, Seidel, Rendering Workshop 2001 BTF( x, l, v) T x, v l + L l, v i ( ) z ρ i, x( ) view-dependent shadowing and masking term area foreshortening Previous Work Efficient Cloth Modeling and Rendering Daubert, Lensch, Heidrich,, Seidel, Rendering Workshop 2001 view-dependent occlusion factor evaluated per color channel changechange of perceived normal restricted basedbased on synthesized materials

Work Efficient Cloth Modeling and Rendering Daubert, Lensch, Heidrich,, Seidel, Rendering Workshop 2001 view-dependent

6 Previous Work Towards Interactive Bump Mapping with Anisotropic Shift-Variant BRDFs Kautz,, Seidel, Graphics Hardware 2000 Fast, Arbitrary BRDF Shading for Low- Frequency Lighting Using Spherical Harmonics Kautz, Sloan,, Snyder, Rendering Workshop 2002 Our Approach truly view-dependent perceived normal reflectance properties minimize approximation error suitable for real-time rendering

Spherical Harmonics Kautz, Sloan,, Snyder, Rendering Workshop 2002 Our Approach truly

7 Data Analysis Fitting Lafortune lobes to the entire BTF data for one Texel Fitting a Reflectance Field to the BTF data for one pixel Energy plot for one Texel of the Corduroy Data Set Reflectance Field describes intensity of surface point for varying light and fixed view direction good approximation by lobe-like like model RF ( x, l) a, ( x), b, ( x), c, ( x) l ( ) v v i v i v i i N vi, ( x)

Field describes intensity of surface point for varying light and fixed view direction good

8 Preprocessing: BTF Rendering 1. fit Reflectance Fields RF vi for various view directions v i Runtime: 1. determine current view direction v 2. select closest view directions from {v i } 3. compute color according to RF vi 4. interpolate between individual results BTF Rendering Storage requirements: stack of floating point textures about 400 MB per material employ BTF synthesis algorithm store store indices instead of color values reduces reduces storage to about 25 MB per material

interpolate between individual results BTF Rendering Storage requirements: stack of floating point textures about 400 MB

9 Results Reflectance Field BTF Rendering Textures and Bump-Mapping University of Bonn Computer Graphics Group Müller, Reinhard Klein Results University of Bonn Computer Graphics Group Müller, Reinhard Klein 9

Graphics Group Müller, Reinhard Klein Results

10 Conclusions and Future Work in-depth analysis of measured BTF data new approach to BTF rendering high-quality real-time moderate storage requirements for high- frequency detail materials combine with Image Based Lighting Acknowledgements Funded by European Union under the project RealReflect (IST ) realreflect.org

detail materials combine with Image Based Lighting Acknowledgements Funded by European

Bi-Scale Radiance Transfer

Siggraph 2003 paper: papers_0260, page 1 of 6 Bi-Scale Radiance Transfer Peter-Pike Sloan Xinguo Liu Heung-Yeung Shum John Snyder Microsoft Corporation Microsoft Research Asia Microsoft Research Asia Microsoft