Image - Based Remapping of Material Appearance A. Sztrajman 1 , J. - PowerPoint PPT Presentation

Image - Based Remapping of Material Appearance A. Sztrajman 1 , J. Křivánek 2 , A. Wilkie 2 , T. Weyrich 1 1 University College London, UK 2 Charles University, Czech Republic Eurographics Workshop on Material Appearance Modeling – Helsinki 2017 This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 642841.

Material authoring [Retrieved from Unity forum] SUBSTANCE DESIGNER Unity 1 Image-Based Remapping of Material Appearance / A. Sztrajman, J. Krivanek, A. Wilkie, T. Weyrich

Model incompatibility 1. Different BRDF models used by different softwares 1. No clear way to translate between models 3. We usually don’t have access to the implementations 4. and they change between renderers Image-Based Remapping of Material Appearance / A. Sztrajman, J. Krivanek, A. Wilkie, T. Weyrich

BRDF remapping Reference BRDF model External BRDF model (initial condition) External BRDF model (after remapping) 3 Image-Based Remapping of Material Appearance / A. Sztrajman, J. Krivanek, A. Wilkie, T. Weyrich

BRDF remapping BRDF fitting Nonlinear BRDF model Fitted BRDF optimization of (initial guess) BRDF parameters Reflectance data BRDF remapping Nonlinear External model External model optimization of remapped (initial guess) BRDF parameters Reference model rendering 4 Image-Based Remapping of Material Appearance / A. Sztrajman, J. Krivanek, A. Wilkie, T. Weyrich

Appearance comparison • Spherical geometry • Point light illumination • L 2 metric for comparison • Nonlinear optimization with TRF 5 Image-Based Remapping of Material Appearance / A. Sztrajman, J. Krivanek, A. Wilkie, T. Weyrich

Results Conductors GGX Ashikhmin-Shirley Beckmann Ward Dielectrics Phong 6 Image-Based Remapping of Material Appearance / A. Sztrajman, J. Krivanek, A. Wilkie, T. Weyrich

Results: conductors Ashikhmin-Shirley Ward • RGB Reflectivity • RGB Specular reflectance • Roughness • Roughness Reference Ashikhmin-Shirley BRDF External Remapped GGX BRDF Error 7 Image-Based Remapping of Material Appearance / A. Sztrajman, J. Krivanek, A. Wilkie, T. Weyrich

Results: remapping of conductors Ashikhmin-Shirley Ward • RGB Reflectivity • RGB Specular reflectance • Roughness • Roughness 60 conductors from Mitsuba’s DB 8 Image-Based Remapping of Material Appearance / A. Sztrajman, J. Krivanek, A. Wilkie, T. Weyrich

Results: remapping of conductors Ashikhmin-Shirley Ward • RGB Reflectivity • RGB Specular reflectance • Roughness • Roughness 9 Image-Based Remapping of Material Appearance / A. Sztrajman, J. Krivanek, A. Wilkie, T. Weyrich

Results: remapping of conductors (roundtrip) Ashikhmin-Shirley Ward Ashikhmin-Shirley 10 Image-Based Remapping of Material Appearance / A. Sztrajman, J. Krivanek, A. Wilkie, T. Weyrich

Results: dielectrics Ashikhmin-Shirley Ward • RGB Diffuse reflectance • RGB Diffuse reflectance • IOR • RGB Specular reflectance • Roughness • Roughness Reference Ashikhmin-Shirley BRDF. External Remapped GGX BRDF Error 11 Image-Based Remapping of Material Appearance / A. Sztrajman, J. Krivanek, A. Wilkie, T. Weyrich

Results: remapping of dielectrics Ashikhmin-Shirley Ward • RGB Diffuse reflectance • RGB Diffuse reflectance • IOR • RGB Specular reflectance • Roughness • Roughness [Ashikhmin-Shirley] [Ashikhmin-Shirley] [Ward] [Ward] 12 Image-Based Remapping of Material Appearance / A. Sztrajman, J. Krivanek, A. Wilkie, T. Weyrich

Remapping in two stages External model Remapping of diffuse term (initial guess) Reference (diffuse) External model remapped Reference Reference (specular) External model Remapping of specular term (initial guess) 13 Image-Based Remapping of Material Appearance / A. Sztrajman, J. Krivanek, A. Wilkie, T. Weyrich

Results: 2 - stage remapping of dielectrics Ashikhmin-Shirley Ward • RGB Diffuse reflectance • RGB Diffuse reflectance • IOR • RGB Specular reflectance • Roughness • Roughness 14 Image-Based Remapping of Material Appearance / A. Sztrajman, J. Krivanek, A. Wilkie, T. Weyrich

Remapping in three stages External model External model Remapping with 2-stage remapping both terms (initial guess) remapped 15 Image-Based Remapping of Material Appearance / A. Sztrajman, J. Krivanek, A. Wilkie, T. Weyrich

Results: 3 - stage remapping of dielectrics Ashikhmin-Shirley Ward • RGB Diffuse reflectance • RGB Diffuse reflectance • IOR • RGB Specular reflectance • Roughness • Roughness 16 Image-Based Remapping of Material Appearance / A. Sztrajman, J. Krivanek, A. Wilkie, T. Weyrich

Current work: SVBRDF remapping Diffuse map Glossiness map Specular map 17 Image-Based Remapping of Material Appearance / A. Sztrajman, J. Krivanek, A. Wilkie, T. Weyrich

Conclusions  We presented a scheme for automatic remapping of uniform BRDFs without access to the BRDF implementations.  The remapping procedure has been tested with both dielectric and conductor materials and with multiple BRDF models. Overall the transformation between models is robust, and in the cases where we find instabilities, these are generally located in a well-defined area of parameter space.  When dealing with materials with both diffuse and specular terms, both need to be remapped independently to avoid instabilities. 18 Image-Based Remapping of Material Appearance / A. Sztrajman, J. Krivanek, A. Wilkie, T. Weyrich

Thank you! * We would like to thank Cyrille Damez from allegorithmic for his contribution to the project. 19 Image-Based Remapping of Material Appearance / A. Sztrajman, J. Krivanek, A. Wilkie, T. Weyrich

20 Image-Based Remapping of Material Appearance / A. Sztrajman, J. Krivanek, A. Wilkie, T. Weyrich

21 Image-Based Remapping of Material Appearance / A. Sztrajman, J. Krivanek, A. Wilkie, T. Weyrich

Results: remapping of conductors Ashikhmin-Shirley Ward • RGB Reflectivity • RGB Specular reflectance • Roughness • Roughness 22 Image-Based Remapping of Material Appearance / A. Sztrajman, J. Krivanek, A. Wilkie, T. Weyrich

Results: remapping of conductors Ashikhmin-Shirley Ward • RGB Reflectivity • RGB Specular reflectance • Roughness • Roughness 23 Image-Based Remapping of Material Appearance / A. Sztrajman, J. Krivanek, A. Wilkie, T. Weyrich

Results Geometry used for remapping Original BRDF Remapped BRDF Error 24 Image-Based Remapping of Material Appearance / A. Sztrajman, J. Krivanek, A. Wilkie, T. Weyrich