Modeling the Interaction of Light Between Diffuse Surfaces

Cindy M. Goral, Keenth E. Torrance, Donald P. Greenberg and Bennett Battaile Presented by: Chris Wassenius Modeling the Interaction of Light Between Diffuse Surfaces

Outline • Introduction / Motivation • Local vs Global Illumination • Method • Results • Conclusion • Acknowledgments

Introduction / Motivation • Accounting for global illumination is central in producing realistic scenes. • Most surfaces reflect light diffusely back into the environment. • Diffuse reflections of objects account for most of the lighting in a scene.

Introduction / Motivation Ray Tracing • hard shadows • ambient term needed to simulate global illumination

Introduction / Motivation True Global Illumination • soft shadows • color bleeding • no need for ambient term

Introduction / Motivation • The proposed method, Radiosity, accounts for indirect light surfaces. • Related Work: • Thermal Engineering Radiant heat exchange Energy transport and conservation principles

Outline • Introduction / Motivation • Method • Radiosity Equation • Form Factors • Putting It Together • Results • Conclusion • Acknowledgments

Method • Diffuse reflectors / emitters • Enclosures • Set of surfaces that define the illuminating environment • Form factors • Fraction of the radiant light energy leaving one surface that strikes another surface

Method Bj = radiosity of surface j Ej = rate of direction emmision from surface j ρj = reflectivity of surface j Hj = incident radiant energy arriving at surface j

Method What is the incident radiant energy arriving at surface j? This gives:

Method Computing Form Factors • The intensity of light reflected is constant and uniform from all viewing directions. • Total energy leaving a surface is found by integrating over the hemisphere. • Intensity of light drops proportionally with the distance squared.

Method Computing Form Factors (continued) Putting all this together...

Method Computing Form Factors (continued) Identity Shortcuts 1 2 3

Method Implementation Step 1 - Read in polygon data Step 2 - Subdivide polygons into patches Step 3 - Compute form factors Step 4 – Solve Radiosity Equation Step 5 – Render scene

Outline • Introduction / Motivation • Method • Results • Conclusion • Future Work

Results

Outline • Introduction / Motivation • Method • Results • Conclusion • Pros and Cons • Future work • Acknowledgments

Conclusion • Pros • Approached realism with global illumination • View independent solution • Cons • Computationally expensive • Does not account for occluded surfaces • Does not taking into account specular reflections

Conclusions Future Work: • Account for occluded surfaces (hemicube method) • Optimal polygon subdivision method • Hierarchical storing of patches • Faster form factor calculations

Modeling the Interaction of Light Between Diffuse Surfaces