ICT
GL
Estimating Specular Roughness and Anisotropy from Second Order Spherical Gradient Illumination 

Eurographics Symposium on Rendering 2009 

Abhijeet Ghosh Tongbo Chen Pieter Peers Cyrus A. Wilson Paul Debevec  
USC Institute for Creative Technologies 
Figure 1: Specular reflectance properties ((a)(c)) of a plastic orange estimated using polarized second order spherical gradient illumination conditions. The estimated specular roughness map (c) is used as the perpixel distribution for a TorranceSparrow BRDF to create a rendering (d) that closely matches the validation photograph (e).
Abstract:
We present a novel method for estimating specular roughness and tangent vectors, per surface point, from polarized second order spherical gradient illumination patterns. We demonstrate that for isotropic BRDFs, only three second order spherical gradients are sufficient to robustly estimate spatially varying specular roughness. For anisotropic BRDFs, an additional two measurements yield specular roughness and tangent vectors per surface point. We verify our approach with different illumination configurations which project both discrete and continuous fields of gradient illumination. Our technique provides a direct estimate of the perpixel specular roughness and thus does not require offline numerical optimization that is typical for the measureandfit approach to classical BRDF modeling.
Introduction:
In this work, we estimate spatially varying appearance properties of materials by directly acquiring second order statistics of per surface point specular reflectance. This includes an estimate of perpixel specular roughness as a measure of variance about a mean (e.g., reflection vector), as well as an estimate of the tangent vectors for anisotropic materials. We take a computational illumination approach towards efficient computation of these statistics by employing polarized second order spherical gradient illumination for our measurements. With this approach, we are able to obtain a more complete spatially varying BRDF information for arbitrary objects from observation under just 7 to 9 lighting conditions for isotropic and anisotropic materials respectively. Furthermore, since the proposed method relies on only up to nine distinct illumination conditions with minimal capture time, it is amenable to capturing persurface point roughness parameters of human subjects.
Specular reflectance properties:
results:


Anisotropic BRDF 

Isotropic BRDF 
Material:
Eurographics Symposium on Rendering 2009 Paper:
 egsr2009final.pdf, 15.3 MB. ( Adobe Acrobat )
SIGGRAPH 2009 Talk:
 SIG2009Talk.pdf, 1.92 MB. ( Adobe Acrobat )
Related Projects:
 HighResolution Face Scanning, Eurographics Symposium on Rendering 2007
 Linear Light Source Reflectometry , SIGGRAPH 2003 Conference Proceedings
 Light Stage 1:
 Acquiring the Reflectance Field of a Human Face, SIGGRAPH 2000
 Facial Reflectance Field Demo, SIGGRAPH 2000 Creative Applications Laboratory
 Realistic Human Face Scanning and Rendering, ICT Graphics Lab 2001
 Light Stage 2:
 A Photometric Approach to Digitizing Cultural Artifacts, VAST 2001
 Animatable Facial Reflectance Fields, EGSR 2004
 Reflectance Field Rendering of Human Faces for "SpiderMan 2", SIGGRAPH 2004 Sketch
 Light Stage 5:
 Postproduction ReIllumination of Live Action Using Interleaved Lighting, SIGGRAPH 2004 Poster
 Performance Geometry Capture for Spatially Varying Relighting, SIGGRAPH 2005 Sketch