Lecture13-IlluminationShading

# Lecture13-IlluminationShading - CS 455 Computer Graphics...

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CS 455 – Computer Graphics Illumination & Shading

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What is a Shading Model? A way to paint the object with light We will discuss the common, heuristic shading models: Diffuse Gouraud Phong Not physically based: hacks that work well in practice and are common on most graphics boards
Diffuse Objects For “matte” objects with no shininess Diffuse/matte objects are called Lambertian In general, shading does not vary with viewpoint Example: a piece of paper, chalk board Reflected light is scattered equally in all directions

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Lambertian Surface Obeys Lambert’s Law (from physics) : The color, c , of a surface is proportional to the cosine of the angle between the surface normal and the direction of the light source θ cos rs, unit vecto are and if , cos || |||| || that recall , cos = = l n l n l n l n c θ θ θ n n n l l l
Lambertian Surface Lambert’s Law: As the angle ( θ29 between the surface normal ( n ) and the light direction ( l ) increases, the same amount of light ( A ) falls on a larger surface area ( x ) surface is dimmer Diffuse color is independent of the eye position: As you move from the light location, you see more area, but the amount of light reflected at that angle per visible unit area of surface is proportionally less

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Diffuse Lighting Model ) , 0 max( l n = l r c c color Diffuse reflectance color: fraction of light reflected from the surface (RGB) Light color [0,1] (RGB) Ensures positive light, even when θ > 90 What happens if light source is at infinity? Angle between light and the normal Let’s define a lighting model that captures this n l
Ambient Term Lambertian model produces black for any surface facing away from the light In reality, light bounces off walls, is scattered in the atmosphere, etc., so surfaces facing away from the light

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## This note was uploaded on 03/02/2012 for the course C S 455 taught by Professor Jones,m during the Winter '08 term at BYU.

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Lecture13-IlluminationShading - CS 455 Computer Graphics...

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