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8-Illumination

# 8-Illumination - Illumination Jason Lawrence CS 4810...

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Illumination Jason Lawrence CS 4810: Graphics Acknowledgment: slides by Misha Kazhdan, Allison Klein, Tom Funkhouser, Adam Finkelstein and David Dobkin

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Overview Direct Illumination o Emission at light sources o Direct light at surface points Global illumination o Shadows o Inter-object reflections o Transmissions Refractive Bouncing
Overview Direct Illumination o Emission at light sources o Direct light at surface points Global illumination o Shadows o Inter-object reflections o Transmissions Intersection Testing

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Overview Direct Illumination o Emission at light sources o Direct light at surface points Global illumination o Shadows o Inter-object reflections o Transmissions
Modeling Light Sources I L ( x,y,z, θ , φ , λ ) ... o describes the intensity of energy, o leaving a light source, … o arriving at location(x,y,z), ... o from direction ( θ , φ ), ... o with wavelength λ (x,y,z) Light

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Empirical Models Ideally measure irradiant energy for “all” situations o Too much storage o Difficult in practice λ
Simplified Light Source Models Simple mathematical models: o Point light o Directional light o Spot light

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Point Light Source Models omni-directional point source o intensity (I 0 ), o position (px, py, pz), o factors (k c , k l , k q ) for attenuation with distance (d) d Light (px, py, pz)
Directional Light Source Models point light source at infinity o intensity (I 0 ), o direction (dx,dy,dz) (dx, dy, dz) No attenuation with distance

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Spot Light Source Models point light source with direction o intensity (I 0 ), o position (px, py, pz), o attenuation (k c , k l , k q ) o direction (dx, dy, dz) o cut-off and drop-off ( γ , α ) d Light (px, py, pz) D L γ How can we modify point light to decrease as γ increases?
Spot Light Source Models point light source with direction o intensity (I 0 ), o position (px, py, pz), o attenuation (k c , k l , k q ) o direction (dx, dy, dz) o cut-off and drop-off ( γ , α ) d Light (px, py, pz) D L γ

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Overview Direct Illumination o Emission at light sources o Direct light at surface points Global illumination o Shadows o Transmissions o Inter-object reflections
Overview Direct Illumination o Emission at light sources o Direct light at surface points Global illumination o Shadows o Transmissions o Inter-object reflections

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Modeling Surface Reflectance R s ( θ , φ , λ , γ , ψ ) ... o describes the fraction of incident energy, o arriving from direction ( θ , φ ), ... o with wavelength λ , ... o leaving in direction ( γ , ψ ), … Surface ( θ , φ ) λ ( ψ , γ )
Empirical Models Ideally measure radiant energy for “all” combinations of incident angles o Too much storage o Difficult in practice Surface ( θ , φ ) λ ( ψ , γ )

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Simple Reflectance Model Simple analytic model: o diffuse reflection + o specular reflection + o emission + o “ambient” Surface Based on model proposed by Phong
Simple Reflectance Model Simple analytic model: o diffuse reflection + o specular reflection + o emission + o “ambient” Surface Based on Phong illumination model Based on model proposed by Phong

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Diffuse Reflection Assume surface reflects equally in all directions o Examples: chalk, clay Surface
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