# lecture8 - CSE472 Computer Graphics Illumination and...

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1 CSE472 Computer Graphics Illumination and Shading Light/surface physics The Hall illumination model Chapter 8 + material in notes

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2 CSE472 Computer Graphics Discrete Illumination Models What occurs when light strikes a surface  is quite  complex.   Continuous process Light from infinite angle reflected in infinite directions We are determining intensity of a pixel with… Finite number of lights Finite reflections into space Finite illumination directions Hence, we must have a  discrete model  for lighting  and illumination.
3 CSE472 Computer Graphics Illumination Models What should a lighting model entail? Discrete Lights Types of reflection Commercial systems can be quite complex Most start with a basic model and embellish to  pick up details that are missing

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4 CSE472 Computer Graphics Elements of Lighting at a point N V L R N – The surface normal L – Vector to the light V – Vector to the eye R – Reflection direction
5 CSE472 Computer Graphics Reflection What we need is the amount of light reflected to the eye This consists of several components…

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6 CSE472 Computer Graphics Diffuse Reflection Diffuse reflection  - light reflected in all  directions equally (or close to equally).   Most objects have a component of diffuse  reflection other than pure specular reflection objects like  mirrors.   What determines the intensity of diffuse  reflection?
7 CSE472 Computer Graphics Diffuse Reflection Characteristics Since the intensity is the same in every  direction, the only other characteristic is the  angle between the light and the surface  normal.  The smaller this angle, the greater  the diffuse reflection:

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8 CSE472 Computer Graphics Lambert’s Law w L N L N w ' / cos w w = θ cos ' w w = Diffuse reflection decreases intensity by the cosine of the angle between the light and surface normal. θ
9 CSE472 Computer Graphics Specular Reflection Specular reflection  - If the light hits the  surface and is reflected off mostly  in a  reflection direction, we have specular  reflection. There is usually some diffusion. A perfect specular object (no diffusion at all) is a  mirror.   Most objects have some specular characteristics

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10 CSE472 Computer Graphics Diffuse and Specular colors Typically the colors reflected for diffuse and specular reflection are different Diffuse – Generally the surface appearance Specular – The color of bright highlights, often more white then the surface color
11 CSE472 Computer Graphics Where do these come from?

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## lecture8 - CSE472 Computer Graphics Illumination and...

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