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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
1
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