Graphics Reflection Model kucg korea ac kr Graphics
- Slides: 41
Graphics Reflection Model 고려대학교 컴퓨터 그래픽스 연구실 kucg. korea. ac. kr Graphics Lab @ Korea University
Content KUCG Shading n Light sources n n n Point, distant, and spot lights Phong reflection model Diffuse reflection n Specular reflection n Ambient reflection n n Computation of vectors n Normal vectors, angle of reflection, and transmitted light kucg. korea. ac. kr Graphics Lab @ Korea University
Shading KUCG Determine a color for each filled pixel n How to choose a color n n the color of the light source and of the surfaces determines the color of one or more pixels in the frame buffer kucg. korea. ac. kr Graphics Lab @ Korea University
Light and Matter n KUCG Color is determined by multiple interactions among light sources and reflective surfaces n recursive reflection of light between surfaces accounts for subtle shading Rendering Equation kucg. korea. ac. kr Graphics Lab @ Korea University
Light-Material Interactions n Specular surfaces – mirror n n scatter reflected light in a narrow range of angle Diffuse surfaces – chalk, clay n n KUCG scatter reflected light all directions Translucent surfaces – glass, water n refraction specular surface kucg. korea. ac. kr diffuse surface translucent surface Graphics Lab @ Korea University
Light Sources n KUCG Illumination function I (x, y, z, θ, φ, λ) each point (x, y, z) on the surface n direction of emission (θ, φ) n wavelength λ n light source kucg. korea. ac. kr Graphics Lab @ Korea University
Modeling Light Sources n KUCG Simple mathematical models: ambient light n point light n distant light n spot light n kucg. korea. ac. kr Graphics Lab @ Korea University
Color Sources n KUCG Three-color theory human perceive three primary colors – red, green, and blue n three-component intensity or luminance function n n independent calculations kucg. korea. ac. kr Graphics Lab @ Korea University
Ambient Light n KUCG Uniform lighting n identical at every point in the scene kucg. korea. ac. kr Graphics Lab @ Korea University
Point Sources (1/2) n KUCG Emit light equally in all directions n p 0: point source location n proportional to the inverse square distance point source illuminating a surface kucg. korea. ac. kr Graphics Lab @ Korea University
Point Sources (2/2) n KUCG Large finite size of most light sources umbra: full shadow n penumbra: partial shadow n n Attenuation shadows created by finite-size light source kucg. korea. ac. kr Graphics Lab @ Korea University
Spotlights n KUCG Characterized by a narrow range of angle through which light is emitted ps: apex of a cone n ls: direction of pointing n θ: angle to determine width n spotlight n Distribution of light n concentrate in the center n light intensity drop off attenuation kucg. korea. ac. kr exponent Graphics Lab @ Korea University
Distant Light Sources n KUCG far from the surface vector does not change n location direction parallel light source kucg. korea. ac. kr Graphics Lab @ Korea University
Phong Reflection Model (1/5) KUCG Efficient and close enough approximation to physical reality to produce good renderings n Use 4 vectors n n: normal at p n v: direction from p to the viewer or COP n l: direction from light source n r: direction of reflectance n n 3 types of material-light interactions n ambient, diffuse, and specular kucg. korea. ac. kr vectors used by the Phong model Graphics Lab @ Korea University
Phong Reflection Model (2/5) n KUCG Simple analytic model: Diffuse reflection + n Specular reflection + n Emission + n “Ambient” n Based on model proposed by Phong kucg. korea. ac. kr Graphics Lab @ Korea University
Phong Reflection Model (2/5) n KUCG Simple analytic model: Diffuse reflection + n Specular reflection + n Emission + n “Ambient” n Based on model proposed by Phong kucg. korea. ac. kr Graphics Lab @ Korea University
Diffuse Reflection (1/3) n KUCG Assume surface reflects equally in all directions n Examples: chalk, clay kucg. korea. ac. kr Graphics Lab @ Korea University
Diffuse Reflection (2/3) n KUCG How much light is reflected? Depends on angle of incident light n d. L = d. A cos Q n kucg. korea. ac. kr Graphics Lab @ Korea University
Diffuse Reflection (3/3) n KUCG Lambertian model n Cosine law (dot product) kucg. korea. ac. kr Graphics Lab @ Korea University
Phong Reflection Model (2/5) n KUCG Simple analytic model: Diffuse reflection + n Specular reflection + n Emission + n “Ambient” n Based on model proposed by Phong kucg. korea. ac. kr Graphics Lab @ Korea University
Specular Reflection (1/3) n KUCG Reflection is strongest near mirror angle n Examples: mirrors, metals kucg. korea. ac. kr Graphics Lab @ Korea University
Specular Reflection (2/3) n KUCG How much light is seen? n Depends on angle of incident light and angle to viewer kucg. korea. ac. kr Graphics Lab @ Korea University
Specular Reflection (3/3) n KUCG Phong model n {cos(a)}n kucg. korea. ac. kr Graphics Lab @ Korea University
Phong Reflection Model (2/5) n KUCG Simple analytic model: Diffuse reflection + n Specular reflection + n Emission + n “Ambient” n Based on model proposed by Phong kucg. korea. ac. kr Graphics Lab @ Korea University
Emission n KUCG Represents light emitting directly from polygon Emission ≠ 0 kucg. korea. ac. kr Graphics Lab @ Korea University
Phong Reflection Model (2/5) n KUCG Simple analytic model: Diffuse reflection + n Specular reflection + n Emission + n “Ambient” n Based on model proposed by Phong kucg. korea. ac. kr Graphics Lab @ Korea University
Ambient Term n KUCG Represents reflection of all indirect illumination This is a total hack (avoids complexity of global illumination)! kucg. korea. ac. kr Graphics Lab @ Korea University
Phong Reflection Model (3/5) n KUCG Simple analytic model: Diffuse reflection + n Specular reflection + n Emission + n “Ambient” n kucg. korea. ac. kr Graphics Lab @ Korea University
Phong Reflection Model (4/5) n KUCG Simple analytic model: Diffuse reflection + n Specular reflection + n Emission + n “Ambient” n kucg. korea. ac. kr Graphics Lab @ Korea University
Phong Reflection Model (5/5) n KUCG Sum diffuse, specular, emission, and ambient kucg. korea. ac. kr Graphics Lab @ Korea University
Surface Illumination Calculation (1/2) n KUCG Single light source: kucg. korea. ac. kr Graphics Lab @ Korea University
Surface Illumination Calculation (2/2) n KUCG Multiple light sources: kucg. korea. ac. kr Graphics Lab @ Korea University
Computation of Reflection n Light source and reflection term n Ex. red intensity n Total Intensity kucg. korea. ac. kr KUCG Graphics Lab @ Korea University
Ambient Reflection KUCG Same at every point on the surface n Ambient reflection coefficient n n amount reflected o n n some of light source is absorbed and some is reflected three ambient coefficients – , , and Ambient reflection term can be any of the individual light sources n can be a global ambient term n kucg. korea. ac. kr Graphics Lab @ Korea University
Diffuse Reflection (1/2) n KUCG Characterized by rough surfaces perfectly diffuse surface so rough that there is no preferred angle of reflection n n Lambert’s law n rough surface only the vertical component of light source at noon kucg. korea. ac. kr in the afternoon Lambert’s law Graphics Lab @ Korea University
Diffuse Reflection (2/2) n KUCG Lambert’s law (cont’) Lambert’s law n Diffuse reflection term n incorporate a distance term kucg. korea. ac. kr Graphics Lab @ Korea University
Specular Reflection n KUCG Specular surface is smooth n highlight in the direction of the viewer specular surface n specular highlights Specular reflection term n shininess coefficient α infinite : mirror o 100 < α < 500 : metal o α < 100 : broad highlight o kucg. korea. ac. kr effect of shininess coefficient Graphics Lab @ Korea University
Illumination Equation n KUCG Including the distance term kucg. korea. ac. kr Graphics Lab @ Korea University
Utah Teapots with Different Material Properties kucg. korea. ac. kr KUCG Graphics Lab @ Korea University
Computation of Vectors (1/2) n Normal vectors n n p 1 KUCG n p 0 in Open. GL gl. Normal 3 f(nx, ny, nz); gl. Normal 3 fv(pointer_to_normal) ; p 2 Angle of reflection coplanar condition ① ② by ① and ② kucg. korea. ac. kr mirror Graphics Lab @ Korea University
Computation of Vectors (2/2) n KUCG Halfway vector n half-angle: 2ψ=φ halfway vector n Transmitted light n Snell’s law perfect light transmission kucg. korea. ac. kr Graphics Lab @ Korea University
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