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• Ray Casting• Surface intersection• Visible surface detection

• Ray Tracing• Bounce the ray• Collecting intensity• Technique for global reflection and transmission

• Visible-surface detection• Shadow effects• Transparency• Multiple light-source illumination

• Highly realistic vs. computation time

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• Scene Description• Ray-path

• From the center of projection, through the center of each screen-pixel position

• Assign intensity accumulated along the ray to the pixel• Since there are an infinite number of ray paths, we trace a ligh

t path backward from pixel to the scene.• One ray per pixel(like the scene through pinhole camera)

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• Basic algorithm• Determine surface-intersection for each pixel ray• Identify visible surface• Repeated for secondary rays

• Reflection, refraction rays

• Ray-tracing tree• Left branch : reflection• Right branch : transmission• Define maximum depth• Terminate if it reaches the

preset maximum or strikes a light source• Accumulate the intensity, starting at the bottom(terminal)

• The sum of the attenuated intensities at the root node• If no surfaces are intersected, the pixel is assigned the intensity

of the background

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needs incident and viewing direction vector

Bi-directional ReflectanceDistribution Function

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• The method for describing diffuse reflections• Consider radiant energy transfers between surfaces

• Basic Radiosity Model• Consider the radiant-energy interactions between all surfaces in a scene D

ifferential amount of radiant energy dB leaving each surface point

• Summing the energy contributions over all surfaces

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• Form Factor Fjk

• Consider energy transfer

• From surface j to surface k• , for all k(conservation of energy)

• , for all j(assuming only plane or

convex surface patches)

n

kjkF

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1

0jjF

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Ray Tracing Example

Original scene description Ray Tracing

Random Object InsertedRandom Light Source Inserted

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Inverse Global Illumination[Paul Debevec] – SIGGRAPH ‘99