lec6 - Lighting Special light sources Point sources Distant...

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CSE152, Spring 2011 Intro Computer Vision Introduction to Computer Vision CSE 152 Lecture 6 CSE152, Spring 2011 Intro Computer Vision Lighting • Special light sources – Point sources – Distant point sources – Strip sources – Area sources • Common to think of lighting at infinity (a function on the sphere, a 2-D space) • Completely arbitrary lighting can be represented as a function on the 4-D ray space (radiances) CSE152, Spring 2011 Intro Computer Vision Radiance Power traveling at some point in a specified direction, per unit area perpendicular to the direction of travel, per unit solid angle Units: watts per square meter per steradian : w/(m 2 sr 1 ) Irradiance How much light is arriving at a surface? Irradiance -- power per unit area: W/cm 2 Total power arriving at the surface is given by adding irradiance over all incoming angles x x dA θ d ω ( θ , φ ) CSE152, Spring 2011 Intro Computer Vision Camera’s sensor Measured pixel intensity is a function of irradiance integrated over – pixel’s area – over a range of wavelengths – For some time CSE152, Spring 2011 Intro Computer Vision BRDF Bi-directional Reflectance Distribution Function ρ ( θ in , φ in ; θ out , φ out ) Function of – Incoming light direction: θ in , φ in – Outgoing light direction: θ out , φ out Ratio of incident irradiance to emitted radiance ^ n ( θ in , φ in ) ( θ out , φ out ) CSE152, Spring 2011 Intro Computer Vision Lambertian Surface At image location (u,v), the intensity of a pixel x(u,v) is: E(u,v) = [a(u,v) n (u,v)] [s 0 s ] where a(u,v) is the albedo of the surface projecting to (u,v). n (u,v) is the direction of the surface normal. s 0 is the light source intensity. s
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lec6 - Lighting Special light sources Point sources Distant...

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