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

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