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Princeton COS 426 - Texture Mapping

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1Texture MappingThomas FunkhouserPrinceton UniversityC0S 426, Fall 20003D Rendering Pipeline (for direct illumination)3D PrimitivesModelingTransformationModelingTransformationProjectionTransformationProjectionTransformationClippingClippingLightingLightingImageViewportTransformationViewportTransformationScanConversionScanConversion2D Image Coordinates3D Modeling Coordinates3D World Coordinates3D Camera Coordinates2D Screen Coordinates2D Screen CoordinatesViewingTransformationViewingTransformation3D World Coordinates2D Image CoordinatesTexture mapping2SurfaceImageTextureTextures• Describe color variation in interior of 3D polygonWhen scan converting a polygon, vary pixel colors accordingto values fetched from a textureAngel Figure 9.3Surface Textures• Add visual detail to surfaces of 3D objectsPolygonal modelWith surface texture3Overview• Texture mapping methodsMappingFiltering• Texture mapping applications Modulation texturesIllumination mappingBump mappingEnvironment mappingImage-based renderingNon-photorealistic renderingTexture Mapping• Steps:Define textureSpecify mapping from texture to surfaceLookup texture values during scan conversion(0,0)(1,0)(0,1)uvxyModelingCoordinateSystemImageCoordinateSystemstTextureCoordinateSystem4Texture Mapping• When scan convert, map from …image coordinate system (x,y) tomodeling coordinate system (u,v) totexture image (t,s)(0,0)(1,0)(1,1)(0,1)uvxyModelingCoordinateSystemImageCoordinateSystemstTextureCoordinateSystemTexture MappingChris Buehler & Leonard McMillan, MIT• Texture mapping is a 2D projective transformationtexture coordinate system: (t,s) toimage coordinate system (x,y)5Texture Mapping• Scan conversionInterpolate texture coordinates down/across scan linesDistortion due to bilinear interpolation approximation» Cut polygons into smaller ones, or» Perspective divide at each pixelTexture MappingLinear interpolationof texture coordinatesCorrect interpolationwith perspective divideHill Figure 8.426Overview• Texture mapping methodsMappingFiltering• Texture mapping applicationsModulation texturesIllumination mappingBump mappingEnvironment mappingImage-based renderingNon-photorealistic renderingTexture FilteringAngel Figure 9.4• Must sample texture to determine colorat each pixel in image7Texture FilteringAngel Figure 9.5• Aliasing is a problemPoint samplingArea filteringTexture Filtering• Ideally, use elliptically shaped convolution filtersIn practice, use rectangles8Texture FilteringAngel Figure 9.14• Size of filter depends on projective warpCan prefiltering images» Mip maps» Summed area tablesMagnification MinificationMip Maps• Keep textures prefiltered at multiple resolutionsFor each pixel, linearly interpolate betweentwo closest levels (e.g., trilinear filtering)Fast, easy for hardware9Overview• Texture mapping methodsMappingFiltering• Texture mapping applications Modulation textures!Illumination mapping"Bump mapping#Environment mapping$Image-based rendering%Non-photorealistic renderingModulation textures)))()(((),(SSTTLLLnSDAAEIKIKISRVKLNKIKItsTI ++•+•++=∑• Map texture values to scale factorWood textureTexturevalue10Illumination MappingSSTTLLLnSDAAEIKIKISRVKLNKIKII ++•+•++=∑))()((• Map texture values to surface material parameter&KA'KD(KS)KT*nKT = T(s,t)Bump Mapping• Map texture values to perturbations of surfacenormals11Bump MappingH&B Figure 14.100Environment Mapping• Map texture values to perturbations of surfacenormalsH&B Figure 14.9312Image-Based Rendering• Map photographic textures to provide details forcoarsely detailed polygonal modelNonphotorealistic Rendering13Art-MapsSummary• Texture mapping methods+Mapping,Filtering• Texture mapping applications-Modulation textures.Illumination mapping/Bump mapping0Environment mapping1Image-based rendering2Non-photorealistic


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Princeton COS 426 - Texture Mapping

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