11Texture MappingAdam FinkelsteinPrinceton UniversityC0S 426, Fall 20012SurfaceImageTextureTextures• Describe color variation in interior of 3D polygono When scan converting a polygon, vary pixel colors accordingto values fetched from a textureAngel Figure 9.333D Rendering Pipeline (for direct illumination)3D PrimitivesModelingTransformationModelingTransformationProjectionTransformationProjectionTransformationClippingClippingLightingLightingImageViewportTransformationViewportTransformationScanConversionScanConversion2D Image Coordinates3D Modeling Coordinates3D World Coordinates3D Camera Coordinates2D Screen Coordinates2D Screen CoordinatesViewingTransformationViewingTransformation3D World Coordinates2D Image CoordinatesTexture mapping4Surface Textures• Add visual detail to surfaces of 3D objectsPolygonal modelWith surface texture5Surface Textures• Add visual detail to surfaces of 3D objects[Daren Horley]6Overview• Texture mapping methodso Parameterizationo Mappingo Filtering• Texture mapping applicationso Modulation textureso Illumination mappingo Bump mappingo Environment mappingo Image-based renderingo Non-photorealistic rendering27Parameterizationgeometrygeometry++==imageimagetexture maptexture map• Q: How do we decide where on the geometryeach color from the image should go?8Option: Varieties of projections[Paul Bourke][Paul Bourke]9Option: unfold the surface[Piponi2000]10Option: make an atlas[Sander2001]charts atlas surface11Overview• Texture mapping methodso Parameterizationo Mappingo Filtering• Texture mapping applicationso Modulation textureso Illumination mappingo Bump mappingo Environment mappingo Image-based renderingo Non-photorealistic rendering12Texture Mapping•Steps:o Define textureo Specify mapping from texture to surfaceo Lookup texture values during scan conversion(0,0)(1,0)(0,1)uvxyModelingCoordinateSystemImageCoordinateSystemstTextureCoordinateSystem313Texture Mapping• When scan convert, map from …o image coordinate system (x,y) too modeling coordinate system (u,v) too texture image (t,s)(0,0)(1,0)(1,1)(0,1)uvxyModelingCoordinateSystemImageCoordinateSystemstTextureCoordinateSystem14Texture MappingChris Buehler & Leonard McMillan, MIT• Texture mapping is a 2D projective transformationo texture coordinate system: (t,s) too image coordinate system (x,y)15Texture Mapping• Scan conversiono Interpolate texture coordinates down/across scan lineso Distortion due to bilinear interpolation approximation» Cut polygons into smaller ones, or» Perspective divide at each pixel16Texture MappingLinear interpolationof texture coordinatesCorrect interpolationwith perspective divideHill Figure 8.4217Overview• Texture mapping methodso Parameterizationo Mappingo Filtering• Texture mapping applicationso Modulation textureso Illumination mappingo Bump mappingo Environment mappingo Image-based renderingo Non-photorealistic rendering18Texture FilteringAngel Figure 9.4• Must sample texture to determine colorat each pixel in image419Texture FilteringAngel Figure 9.5• Aliasing is a problemPoint samplingArea filtering20Texture Filtering• Ideally, use elliptically shaped convolution filtersIn practice, use rectangles21Texture FilteringAngel Figure 9.14• Size of filter depends on projective warpo Can prefiltering images» Mip maps»SummedareatablesMagnification Minification22Mip Maps• Keep textures prefiltered at multiple resolutionso For each pixel, linearly interpolate betweentwo closest levels (e.g., trilinear filtering)o Fast, easy for hardware23Summed-area tables• Keep at each texel the sum of all values down & righto To compute sum of all values within a rectangle,simply subtract two entrieso Better ability to capture very oblique projectionso But, cannot store values in a single byteS1S224Overview• Texture mapping methodso Parameterizationo Mappingo Filtering• Texture mapping applicationso Modulation textureso Illumination mappingo Bump mappingo Environment mappingo Image-based renderingo Non-photorealistic rendering525Modulation textures)))()(((),(SSTTLLLnSDAAEIKIKISRVKLNKIKItsTI ++•+•++=∑Map texture values to scale factorWood textureTexturevalue26Illumination MappingSSTTLLLnSDAAEIKIKISRVKLNKIKII ++•+•++=∑))()((Map texture values to surface material parametero KAo KDo KSo KTo nKT=T(s,t)27Bump MappingMap texture values to perturbations of surface normals28Bump MappingH&B Figure 14.10029Environment MappingMap texture values to perturbations of surface normalsH&B Figure 14.9330Image-Based RenderingMap photographic textures to provide details forcoarsely detailed polygonal model631Nonphotorealistic Rendering32Art-Maps33Summary• Texture mapping methodso Parameterizationo Mappingo Filtering• Texture mapping applicationso Modulation textureso Illumination mappingo Bump mappingo Environment mappingo Image-based renderingo Non-photorealistic
View Full Document
Unlocking...