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

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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

Results

Results

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