VisualizationandNonphotorealisticRendering Adrien TreuilleCarnegie Mellon UniverstiyProject 4 CompetitionTop 4 Artifacts get an IPod Touch!(decided by vote of TAs + Graphics Lab)Artifact can be movie/image/anything else...Thank you AMD...Outline•Visualization•Non-photorealistic Rendering•Cutaway Illustration•Contour Drawing•Good photographs.•Map Drawing•PaintingOutline•Visualization•Non-photorealistic Rendering•Cutaway Illustration•Contour Drawing•Good photographs.•Map Drawing•PaintingVisualization•Goal: Use computer graphics to understand data.•For virtual every data type there is a corresponding visualization.•The importance of graphics!http://medvis.vrvis.at/fileadmin/hvr/images/headlarge.jpgNumerical Datahttp://www.manifold.net/news/fly_through.jpgGraphshttp://www.wandora.org/wandora/wiki/images/Tree_graph_example.gifGraphshttp://www.designinginteractions.com/chapters/7Geographic Datahttp://flowingdata.com/wp-content/plugins/yet-another-photoblog/cache/g_econ.6zhzwniskpgcwwgs00okoco4s.7dm680981og04ocskgcsckco4.th.jpegFlow Visualizationhttp://www.faculty.iu-bremen.de/llinsen/publications/ParkYuHotzKreylosLinsenHamann06.jpg3D Volume Datahttp://medvis.vrvis.at/fileadmin/hvr/images/headlarge.jpgExampleVolume Rendering•Visualize Large dataset for scientific / medical application.•Generally do not start with a 3D model.Scientific VisualizationScientific Visualization• Visualize large datasets in scientific and medical applications• Generally do not start with a 3D modelCT Scan - whiter means higher radiodensityCT Scan - White means higher radiodensity.OUTPUTINPUTData Format•A cube of density values.Large DatasetsScientific VisualizationScientific Visualization• Visualize large datasets in scientific and medical applications• Generally do not start with a 3D modelCT Scan - whiter means higher radiodensityCT Scan - White means higher radiodensity.OUTPUTINPUT•CT or MRI:•e.g. 512×512×200 ≈ 50MB•Visible Human: •512×512×1734 ≈ 433MBTwo Options•Surface Rendering•Volume RenderingTwo Options•Surface Rendering•Volume RenderingSurface Rendering•Threshold volume data.Marching Cube TessellationsMarching Cube Tessellations• Generalize marching squares, just more cases• Interpolate as in 2D• Ambiguities similar to 2D•Then run our favorite algorithm....•Hint: rhymes with “starching dudes”Two Options•Surface Rendering•Volume RenderingTwo Options•Surface Rendering•Volume RenderingVolume Rendering•Some data better visualized as a volume, not a surface.•Idea: Use voxels and transparency.RaytracedIsosurfaceVolumeRenderingVolume Rendering PipelineVolume Rendering PipelineData setsRenderingSample VolumeTransfer functionImage• Data volumes come in all types: tissue density (CT), wind speed, pressure, temperature, value of implicit function.• Data volumes are used as input to a transfer function, which produces a sample volume of colors and opacities as output. – Typical might be a 256x256x64 CT scan• That volume is rendered to produce a final image.Transfer FunctionsTransfer Functions• Transform scalar data values to RGBA values• Apply to every voxel in volume• Highly application dependent• Start from data histogramTransfer Function ExampleTransfer Function ExampleMantle ConvectionScientific Computing and Imaging (SCI)University of UtahThree Options•Ray Casting•Splatting•3D TexturesVolume Ray CastingVolume Ray Casting• Ray Casting– Integrate color and opacity along the ray– Simplest scheme just takes equal steps along ray, sampling opacity and color– Grids make it easy to find the next cellSplattingSplatting• Alternative to ray tracing• Assign shape to each voxel (e.g., sphere or Gaussian)• Project onto image plane (splat)• Draw voxels back-to-front• Composite (a-blend)3D Textures3D Textures• Alternative to ray tracing, splatting• Build a 3D texture (including opacity)• Draw a stack of polygons, back-to-front• Efficient if supported in graphics hardware• Few polygons, much texture memory3D RGBA textureDraw back to frontViewpointThree Options•Ray Casting•Splatting•3D TexturesVolume Ray CastingVolume Ray Casting• Ray Casting– Integrate color and opacity along the ray– Simplest scheme just takes equal steps along ray, sampling opacity and color– Grids make it easy to find the next cellDraw back to frontVolume Ray CastingVolume Ray Casting• Ray Casting– Integrate color and opacity along the ray– Simplest scheme just takes equal steps along ray, sampling opacity and color– Grids make it easy to find the next cellTrilinear InterpolationTrilinear Interpolation• Interpolate to compute RGBA away from grid• Nearest neighbor yields blocky images• Use trilinear interpolation• 3D generalization of bilinear interpolationNearestneighborTrilinearinterpolationTrilinear InterpolationTrilinear InterpolationBilinear interpolationTrilinear interpolationThree Options•Ray Casting•Splatting•3D TexturesVolume Ray CastingVolume Ray Casting• Ray Casting– Integrate color and opacity along the ray– Simplest scheme just takes equal steps along ray, sampling opacity and color– Grids make it easy to find the next cellDraw back to frontThree Options•Ray Casting•Splatting•3D TexturesSplattingSplatting• Alternative to ray tracing• Assign shape to each voxel (e.g., sphere or Gaussian)• Project onto image plane (splat)• Draw voxels back-to-front• Composite (a-blend)Draw back to frontSplattingSplatting• Alternative to ray tracing• Assign shape to each voxel (e.g., sphere or Gaussian)• Project onto image plane (splat)• Draw voxels back-to-front• Composite (a-blend)ExampleThree Options•Ray Casting•Splatting•3D TexturesSplattingSplatting• Alternative to ray tracing• Assign shape to each voxel (e.g., sphere or Gaussian)• Project onto image plane (splat)• Draw voxels back-to-front• Composite (a-blend)Draw back to frontThree Options•Ray Casting•Splatting•3D Textures3D Textures3D Textures• Alternative to ray tracing, splatting• Build a 3D texture (including opacity)• Draw a stack of polygons, back-to-front• Efficient if supported in graphics hardware• Few polygons, much texture memory3D RGBA textureDraw back to frontViewpoint3D Textures3D Textures• Alternative to ray tracing, splatting• Build a 3D texture (including opacity)• Draw a stack of polygons, back-to-front• Efficient if supported in
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