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Subsurface scattering 205 other more traditional lighting models, allows the creation of different materials such as marble, jade and wax. Potentially, problems can arise if models are not convex, but depth peeling [3] can be used to avoid the issue. Similarly, depth peeling can be used to account for varying densities beneath the surface, such as bone or muscle, to give a more accurate scattering model. As can be seen in the image of the wax head to the right, light isn’t diffused when passing through object using this technique; back features are clearly shown. One solution to this is to take multiple samples at different points on surface of the depth map. Alternatively, a different approach to approximation can be used, known as texture-space diffusion. Texture Space Diffusion As noted at the start of the section, one of the more obvious effects of subsurface scattering is a general blurring of the diffuse lighting. Rather than arbitrarily modifying the diffuse function, diffusion can be more accurately modeled by simulating it in texture space. This technique was pioneered in rendering faces in The Matrix Reloaded, [4] but has recently fallen into the realm of real-time techniques. The method unwraps the mesh of an object using a vertex shader, first calculating the lighting based on the original vertex coordinates. The vertices are then remapped using the UV texture coordinates as the screen position of the vertex, suitable transformed from the [0, 1] range of texture coordinates to the [-1, 1] range of normalized device coordinates. By lighting the unwrapped mesh in this manner, we obtain a 2D image representing the lighting on the object, which can then be processed and reapplied to the model as a light map. To simulate diffusion, the light map texture can simply be blurred. Rendering the lighting to a lower-resolution texture in itself provides a certain amount of blurring. The amount of blurring required to accurately model subsurface scattering in skin is still under active research, but performing only a single blur poorly models the true effects. [5] To emulate the wavelength dependent nature of diffusion, the samples used during the (Gaussian) blur can be weighted by channel. This is somewhat of an artistic process. For human skin, the broadest scattering is in red, then green, and blue has very little scattering. A major benefit of this method is its independence of screen resolution; shading is performed only once per texel in the texture map, rather than for every pixel on the object. An obvious requirement is thus that the object have a good UV mapping, in that each point on the texture must map to only one point of the object. Additionally, the use of texture space diffusion causes implicit soft shadows, alleviating one of the more unrealistic aspects of standard shadow mapping. References [1] Krishnaswamy, A; Baronoski, GVG (2004). "A Biophysically-based Spectral Model of Light Interaction with Human Skin" (http:/ / eg04. inrialpes. fr/ Programme/ Papers/ PDF/ paper1189. pdf). Computer Graphics Forum (Blackwell Publishing) 23 (3): 331. doi:10.1111/j.1467-8659.2004.00764.x. . [2] Green, Simon (2004). "Real-time Approximations to Subsurface Scattering". GPU Gems (Addison-Wesley Professional): 263–278. [3] Nagy, Z; Klein, R (2003). "Depth-Peeling for Texture-based Volume Rendering" (http:/ / cg. cs. uni-bonn. de/ docs/ publications/ 2003/ nagy-2003-depth. pdf). 11th Pacific Conference on Computer Graphics and Applications: 429. . [4] Borshukov, G; Lewis, J. P. (2005). "Realistic human face rendering for "The Matrix Reloaded"" (http:/ / www. virtualcinematography. org/ publications/ acrobat/ Face-s2003. pdf). Computer Graphics (ACM Press). . [5] d’Eon, E (2007). "Advanced Skin Rendering" (http:/ / developer. download. nvidia. com/ presentations/ 2007/ gdc/ Advanced_Skin. pdf). GDC 2007. .
Subsurface scattering 206 External links • Henrik Wann Jensen's subsurface scattering website (http:/ / graphics. ucsd. edu/ ~henrik/ images/ subsurf. html) • An academic paper by Jensen on modeling subsurface scattering (http:/ / graphics. ucsd. edu/ ~henrik/ papers/ bssrdf/ ) • Maya Tutorial - Subsurface Scattering: Using the Misss_Fast_Simple_Maya shader (http:/ / www. highend3d. com/ maya/ tutorials/ rendering_lighting/ shaders/ 135. html) • 3d Studio Max Tutorial - The definitive guide to using subsurface scattering in 3dsMax (http:/ / www. mrbluesummers. com/ 3510/ 3d-tutorials/ 3dsmax-mental-ray-sub-surface-scattering-guide/ ) Surface caching Surface caching is a computer graphics technique pioneered by John Carmack, first used in the computer game Quake to apply lightmaps to level geometry. Carmack's technique was to combine lighting information with surface textures in texture-space when primitives became visible (at the appropriate mipmap level), exploiting temporal coherence for those calculations. As hardware capable of blended multi-texture rendering (and later pixel shaders) became more commonplace, the technique became less common, being replaced with screenspace combination of lightmaps in rendering hardware. Surface caching contributed greatly to the visual quality of Quakes' software rasterized 3d engine on Pentium microprocessors, which lacked dedicated graphics instructions. . Surface caching could be considered a precursor to the more recent megatexture technique in which lighting and surface decals and other procedural texture effects are combined for rich visuals devoid of un-natural repeating artefacts. External links • Quake's Lighting Model: Surface Caching [1] - an in-depth explanation by Michael Abrash References [1] http:/ / www. bluesnews. com/ abrash/ chap68. shtml
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3D Rendering PDF generated using th
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Image-based lighting 64 Image plane
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References Article Sources and Cont
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3D rendering 2 Non real-time Animat
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3D rendering 4 The shaded three-dim
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Ambient occlusion 6 ambient occlusi
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Ambient occlusion 8 • ShadeVis (h
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Anisotropic filtering 10 will only
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Beam tracing 12 Beam tracing Beam t
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Bilinear filtering 14 Are all true.
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Binary space partitioning 16 togeth
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Binary space partitioning 18 Other
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Binary space partitioning 20 [1] Bi
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Bounding interval hierarchy 22 Prop
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Bounding volume 24 bounding boxes b
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Bump mapping 26 Bump mapping Bump m
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CatmullClark subdivision surface 28
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CatmullClark subdivision surface 30
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Conversion between quaternions and
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Cube mapping 34 Advantages Cube map
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Cube mapping 36 Related A large set
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Diffuse reflection 38 2), or, of co
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Displacement mapping 40 Meaning of
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DooSabin subdivision surface 42 Ext
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False radiosity 44 False radiosity
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Geometry pipelines 46 Geometry pipe
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Global illumination 48 Rendering wi
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Gouraud shading 50 Gouraud shading
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Graphics pipeline 52 Graphics pipel
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Graphics pipeline 54 References 1.
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Hidden surface determination 56 imp
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High dynamic range rendering 58 Hig
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High dynamic range rendering 60 Ton
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High dynamic range rendering 62 Fro
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High dynamic range rendering 64 •
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Irregular Z-buffer 66 Applications
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Lambert's cosine law 68 than would
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Lambertian reflectance 70 Lambertia
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Level of detail 72 Well known appro
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Level of detail 74 Hierarchical LOD
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Newell's algorithm 76 Newell's algo
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Non-uniform rational B-spline 78 Us
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Non-uniform rational B-spline 80 of
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Non-uniform rational B-spline 82 ar
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Non-uniform rational B-spline 84 Ex
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Normal mapping 86 How it works To c
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OrenNayar reflectance model 88 Oren
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OrenNayar reflectance model 90 , ,
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Painter's algorithm 92 The algorith
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Parallax mapping 94 • Parallax Ma
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Particle system 96 A cube emitting
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Path tracing 98 History Further inf
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Path tracing 100 Scattering distrib
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Phong reflection model 102 Visual i
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Phong reflection model 104 Because
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Phong shading 106 Visual illustrati
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Photon mapping 108 Rendering (2nd p
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Photon tracing 110 Advantages and d
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Potentially visible set 112 • Can
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Potentially visible set 114 Externa
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Procedural generation 116 increases
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Procedural generation 118 • Softi
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Procedural generation 120 Reference
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Procedural texture 122 Self-organiz
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Procedural texture 124 References [
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3D projection 126 The distance of t
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Quaternions and spatial rotation 12
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Radiosity 140 Overview of the radio
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Radiosity 142 This is sometimes kno
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Radiosity 144 References [1] " Mode
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Ray casting 146 the light will reac
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Ray tracing 148 Typically, each ray
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Ray tracing 150 independence of eac
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Ray tracing 152 On June 12, 2008 In
Page 159 and 160: Reflection 154 Reflection Reflectio
Page 161 and 162: Reflection 156 Glossy Reflection Fu
Page 163 and 164: Reflection mapping 158 Cube mapping
Page 165 and 166: Render Output unit 160 Render Outpu
Page 167 and 168: Rendering 162 • indirect illumina
Page 169 and 170: Rendering 164 Ray tracing Ray traci
Page 171 and 172: Rendering 166 Academic core The imp
Page 173 and 174: Rendering 168 • 1984 Distributed
Page 175 and 176: Retained mode 170 Retained mode In
Page 177 and 178: Scanline rendering 172 Comparison w
Page 179 and 180: Screen Space Ambient Occlusion 174
Page 181 and 182: Screen Space Ambient Occlusion 176
Page 183 and 184: Shadow mapping 178 Algorithm overvi
Page 185 and 186: Shadow mapping 180 Drawing the scen
Page 187 and 188: Shadow mapping 182 Further reading
Page 189 and 190: Shadow volume 184 There is also a p
Page 191 and 192: Shadow volume 186 The depth fail me
Page 193 and 194: Silhouette edge 188 Silhouette edge
Page 195 and 196: Specular highlight 190 Specular hig
Page 197 and 198: Specular highlight 192 normalized o
Page 199 and 200: Sphere mapping 194 Sphere mapping I
Page 201 and 202: Stencil codes 196 Stencil codes Ste
Page 203 and 204: Stencil codes 198 Stencils The shap
Page 205 and 206: Stencil codes 200 [7] Wellein, G et
Page 207 and 208: Subdivision surface 202 used a four
Page 209: Subsurface scattering 204 Subsurfac
Page 213 and 214: Surface normal 208 If a (possibly n
Page 215 and 216: Surface normal 210 Normal in geomet
Page 217 and 218: Texture filtering 212 Texture filte
Page 219 and 220: Texture mapping 214 Texture mapping
Page 221 and 222: Texture mapping 216 constant distan
Page 223 and 224: Texture synthesis 218 • Structure
Page 225 and 226: Texture synthesis 220 Pattern-based
Page 227 and 228: Texture synthesis 222 • Micro-tex
Page 229 and 230: UV mapping 224 A UV map can either
Page 231 and 232: Vertex 226 Polytope vertices are re
Page 233 and 234: Vertex Buffer Object 228 //Make the
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Page 237 and 238: Vertex Buffer Object 232 vertexes *
Page 239 and 240: Virtual actor 234 Virtual actor A v
Page 241 and 242: Virtual actor 236 exercises, and ev
Page 243 and 244: Volume rendering 238 Volume ray cas
Page 245 and 246: Volume rendering 240 Maximum intens
Page 247 and 248: Volume rendering 242 Image-based me
Page 249 and 250: Volumetric lighting 244 References
Page 251 and 252: Voxel 246 • Outcast, a game made
Page 253 and 254: Z-buffering 248 Z-buffering In comp
Page 255 and 256: Z-buffering 250 } } display COLOR a
Page 257 and 258: Z-fighting 252 Z-fighting Z-fightin
Page 259 and 260: Appendix 3D computer graphics softw
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3D computer graphics software 256
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3D computer graphics software 258
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3D computer graphics software 260 2
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Article Sources and Contributors 26
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Article Sources and Contributors 26
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Image Sources, Licenses and Contrib
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Image Sources, Licenses and Contrib
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