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Class5

# Class5 - Class 5 Illumination and Shading HW4...

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Class 5 Illumination and Shading HW4 Ulrich Neumann CS580 (Computer Graphics Rendering)

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Illumination and shading Illumination (lighting) and shading models simulation of light interactions with scene light sources, geometry, propagation, interaction with surfaces, imaging process in camera
Shading Examples Images courtesy of Watt, Watt & Watt, and Foley & van Dam

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Global versus Local Illumination 2 P 1 P Indirect Illumination Direct Illumination
Global versus Local Illumination Global Illumination Considers indirect illumination Reflection Refraction Shadows Local Illumination Only considers direct illumination No reflection No refraction Simple shadows possible

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Global versus Local Illumination Images courtesy of Foley & van Dam, Computer Graphics We start with simple local illumination and then extend those concepts/models to global illumination
Radiance Radiance: Power per unit projected source area (A) perpendicular to the ray, per unit solid angle in the direction of the ray dA N the approximation holds for small A and Ω , L is the radiance ( W · m -2 · sr -1 ), Φ is the radiant flux or power ( W ), θ is the angle between the surface normal and the specified direction, A is the area of the source ( m 2 ), and Ω is the solid angle ( sr ).

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Light Source Radiant Intensity Radiant Intensity per steradian Ie(x) = power/sr (Watts/steradian) constant in vacuum at all distances Solid angle sr = surface area (a) of portion of sphere divided by r 2 , sr = a/r 2 Area of sphere surface = 4 pi r 2 sr = (4pi r 2 )/r 2 , sr = 4pi steradians over sphere - independent of radius Ie is constant for fixed solid angle (at any distance) J = We = Watt/m 2 Radiosity or Power Density falls off with square of distance
Light Intensity Ie

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