A system for interactive display and rendering of BRDF models Adri - PowerPoint PPT Presentation

A system for interactive display and rendering of BRDF models Adrià Forés Herranz Advisors: Sumanta N. Pattanaik Carles Bosch

Importance of materials

Overview Analytic models General Measured Display representation data Simulated data Fitting Render

Outline • Previous Work • Input Models • Display • Fitting • Rendering • Simulation • Conclusions and Future Work

Outline • Previous Work • Input Models Analytic • Display models General Measured Display • Fitting representation data Simulated • Rendering data Fitting Render • Simulation • Conclusions and Future Work

Outline • Previous Work • Input Models • Display • Fitting • Rendering • Simulation • Conclusions and Future Work

Previous Work • Currently there does not exist a system to work on materials • bv - a BRDF browser

Previous Work • Currently there does not exist a system to work on materials • bv - a BRDF browser

BRDF • Bidirectional reflectance function (BRDF) ‣ 4 Dimensional function ‣ Spherical coordinates

BRDF: Properties • Helmholtz reciprocity • Energy conservation • Isotropy vs Anisotropy

Input Models Analytic models General Measured Display representation data Simulated data Fitting Render

Analytic models General Measured Display representation data Analytical Models Simulated data Fitting Render • Lambertian • Phong • Lafortune • Ward • Ashikhmin • Cook-Torrance

Analytic models General Measured Display representation data Analytical Models Simulated data Fitting Render • Lambertian • Phong • Lafortune • Ward • Ashikhmin • Cook-Torrance

Analytic models General Measured Display representation data Analytical Models Simulated data Fitting Render • Lambertian • Phong • Lafortune • Ward • Ashikhmin • Cook-Torrance

Analytic models General Measured Display representation data Analytical Models Simulated data Fitting Render • Lambertian • Phong • Lafortune • Ward • Ashikhmin • Cook-Torrance

Analytic models General Measured Display representation data Analytical Models Simulated data Fitting Render • Lambertian • Phong • Lafortune • Ward • Ashikhmin • Cook-Torrance

Analytic models General Measured Display representation data Real World Materials Simulated data Fitting Render

Analytic models General Measured Display representation data Real World Materials Simulated data Fitting Render + + =

Analytic models General Measured Display representation data Measured Data Simulated data Fitting Render • Gonioreflectometer Main idea [DVGNK99] [MWL*99]

Analytic models General Measured Display representation data Measured data Simulated data Fitting Render • MERL library [MPBM03] ‣ 330 images for each material

Analytic models General Measured Display representation data Measured data Simulated data Fitting Render • MPI’s Car Paint library [GCG*05] ‣ 256 images for each material

Analytic models General Measured Display representation data Simulated Simulated data Fitting Render • Some attempts has been made [CMS87,WAT92] • Mostly in optics literature • e.g. Scatmech C++ library

Overview Analytic models General Measured Display representation data Simulated data Fitting Render

Analytic models General Measured Display representation data Display Simulated data Fitting Render • Display the BRDF shape to understand how a material reflects the incident light. • 4 Dimensional Function. ‣ Given a fixed incoming direction (2D), the result in all the outgoing directions is represented (2D). • Allow the user to change the incoming direction

Analytic models General Measured Display representation data Display Simulated data Fitting Render • Geodesic hemisphere • Vertex displacement to match the BRDF shape: ‣ BRDF evaluated per vertex, only possible with analytical models ‣ Adaptive texture-based evaluation: A texture indexed by ϴ and Φ stores the precomputed BRDF ‣ Simply by using points

Analytic models General Measured Display representation data Display - Analytic Simulated data Fitting Render

Analytic models General Measured Display representation data Display - Simulated Simulated data Fitting Render

Analytic models General Measured Display representation data Display - Measured Simulated data Fitting Render

Overview Analytic models General Measured Display representation data Simulated data Fitting Render

Analytic models General Measured Display representation data Fitting Simulated data Fitting Render • Approximate a set of data with an analytical model • Non-linear optimizer ‣ Levenberg-Marquardt • The user is able to set the initial guess values for the optimization step to see how they approximate the data

Analytic models High Computational General Measured Display representation data Simulated data Fitting Render Cost • System of equations defined by the input data ‣ e.g. a material from the MERL library defines 16384 data points • The number of parameters to optimize grow with the number of lobes used

Analytic models General Measured Display representation data Non-linear estimation Simulated data Fitting Render • Combination of linear and non-linear steps during the iterative optimization process ‣ Linear optimization for the scaling factors ‣ Non-linear optimization for the lobe parameters

Analytic models General Measured Display representation data Display Fitting Results Simulated data Fitting Render

Overview Analytic models General Measured Display representation data Simulated data Fitting Render

Analytic models General Measured Display representation data Rendering Simulated data Fitting Render • Point light • Environment light ‣ HDR Environment Map [CK07a, CK07b]

Analytic models General Measured Display representation data Rendering Simulated data Fitting Render • Point light • Environment light ‣ HDR Environment Map [CK07a, CK07b]

Analytic models General Measured Display representation data Rendering Simulated data Fitting Render • Point light • Environment light ‣ HDR Environment Map [CK07a, CK07b]

Analytic models General Measured Display representation data Point light Simulated data Fitting Render • Compute the BRDF on the fragment shader

Analytic models Lighting equation General Measured Display representation data Simulated data Fitting Render • General • Discretized

Analytic models Monte Carlo General Measured Display representation data Simulated data Fitting Render Integration

Analytic models General Measured Display representation data Importance Sampling Simulated data Fitting Render • Choose a few random samples • Selected according to the PDF

Analytic models Mipmap Filtered General Measured Display representation data Simulated data Fitting Render Samples

Analytic models Rendering a fitted General Measured Display representation data Simulated data Fitting Render material

Overview Analytic models General Measured Display representation data Simulated data Fitting Render

Analytic models General Measured Display representation data Origin of BRDFs Simulated data Fitting Render • surface interaction • subsurface interaction

Analytic models General Measured Display representation data Origin of BRDFs Simulated data Fitting Render • surface interaction • subsurface interaction

Analytic models General Measured Display representation data Origin of BRDFs Simulated data Fitting Render • surface interaction • subsurface interaction

Analytic models General Measured Display representation data Origin of BRDFs Simulated data Fitting Render • surface interaction • subsurface interaction

Analytic models General Measured Display representation data Origin of BRDFs Simulated data Fitting Render • surface interaction • subsurface interaction

Analytic models General Measured Display representation data Simulation Simulated data Fitting Render • Given a material structure, obtain its BRDF Material structure Reflected Ray Tracer BRDF shape directions Light direction • Performing this operation with different light directions the full BRDF is obtained • Light is assumed to be parallel as the simulation is done at microscopic level

Analytic Height Field Simulation models General Measured Display representation data Simulated data Fitting Render Material Structure • Relief Map