Shade - Illumination and Shading Chapter 10 Intro. to...

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Illumination and Shading Chapter 10 Intro. to Computer Graphics Spring 2009, Y. G. Shin
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Illumination and Shading Given: scene specification (object positions, optical properties of the surface, viewer position, viewing direction, ……) Find: intensity for each pixel viewer image plane light
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Illumination Models (Lighting model, Shading model) Photorealism in computer graphics depends on Accurate representations of surface properties Good physical descriptions of the lighting effects Rendering needs a model of lighting Physically more correct model: the intensity reflected from every point depends on the intensity from every other points – global illumination Simplistic model: the intensity depends only on the direct illumination due to light sources – local illumination
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Light Sources Point light sources Emitting radiant energy at a single point Specified with its position and the color of the emitted light Infinitely distant light sources A large light source, such as sun, that is very far from a scene Little variation in its directional effects Specified with its color value and a fixed direction for the light rays © Arjan Kok
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Light Sources Directional light sources Produces a directional beam of light Spotlight effects Area light sources
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Light Sources Radial intensity attenuation As radiant energy travels, its amplitude is attenuated by the factor Sometimes, more realistic attenuation effects can be obtained with an inverse quadratic function of distance The intensity attenuation is not applied to light sources at infinity because all points in the scene are at a nearly equal distance from a far-off source 2 / 1 d + + = local is source if 1 infinity at is source if 0 . 1 2 2 1 0 d a d a a f
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Light Sources Angular intensity attenuation For a directional light, we can attenuate the light intensity angularly as well as radially α n f cos ) ( =
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Surface Lighting Effects An illumination model computes the lighting effects for a surface using the various optical properties Degree of opacity, color reflectance, surface texture The local illumination model describes the way incident light reflects from an opaque surface Diffuse, ambient, specular reflections Simple approximation of actual physical models This model is also known as: light reflection model Phong illumination model reflectance model
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Ambient Light Multiple reflection of nearby objects (light-reflecting sources) yields a uniform illumination Ambient light is independent of light sources and viewer position Ambient illumination is constant for an object, without regard to directions of faces : the incident ambient intensity : ambient reflection coefficient, the proportion reflected away from the surface a a I k I = a I a k Indirect illumination can be computed much better using other model such as radiosity
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and are function over all wavelengths .
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This note was uploaded on 04/29/2010 for the course CSE 4190.411 taught by Professor Shinyeonggil during the Fall '08 term at Seoul National.

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Shade - Illumination and Shading Chapter 10 Intro. to...

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