VisualizationandNonphotorealisticRendering Adrien TreuilleCarnegie Mellon UniverstiySaturday, February 27, 2010Outline•Visualization•Non-photorealistic Rendering•Cutaway Illustration•Contour Drawing•Good photographs.•Map Drawing•PaintingSaturday, February 27, 2010Outline•Visualization•Non-photorealistic Rendering•Cutaway Illustration•Contour Drawing•Good photographs.•Map Drawing•PaintingSaturday, February 27, 2010Visualization•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.jpgSaturday, February 27, 2010Numerical Datahttp://www.manifold.net/news/fly_through.jpgSaturday, February 27, 2010Graphshttp://www.wandora.org/wandora/wiki/images/Tree_graph_example.gifSaturday, February 27, 2010Graphshttp://www.designinginteractions.com/chapters/7Saturday, February 27, 2010Geographic Datahttp://flowingdata.com/wp-content/plugins/yet-another-photoblog/cache/g_econ.6zhzwniskpgcwwgs00okoco4s.7dm680981og04ocskgcsckco4.th.jpegSaturday, February 27, 2010Flow Visualizationhttp://www.faculty.iu-bremen.de/llinsen/publications/ParkYuHotzKreylosLinsenHamann06.jpgSaturday, February 27, 20103D Volume Datahttp://medvis.vrvis.at/fileadmin/hvr/images/headlarge.jpgSaturday, February 27, 2010ExampleSaturday, February 27, 2010Volume 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.OUTPUTINPUTSaturday, February 27, 2010Data Format•A cube of density values.Saturday, February 27, 2010Large 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 ≈ 433MBSaturday, February 27, 2010Two Options•Surface Rendering•Volume RenderingSaturday, February 27, 2010Two Options•Surface Rendering•Volume RenderingSaturday, February 27, 2010Surface 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”Saturday, February 27, 2010Two Options•Surface Rendering•Volume RenderingSaturday, February 27, 2010Two Options•Surface Rendering•Volume RenderingSaturday, February 27, 2010Volume Rendering•Some data better visualized as a volume, not a surface.•Idea: Use voxels and transparency.RaytracedIsosurfaceVolumeRenderingSaturday, February 27, 2010Volume 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. Saturday, February 27, 2010Transfer FunctionsTransfer Functions• Transform scalar data values to RGBA values• Apply to every voxel in volume• Highly application dependent• Start from data histogramSaturday, February 27, 2010Transfer Function ExampleTransfer Function ExampleMantle ConvectionScientific Computing and Imaging (SCI)University of UtahSaturday, February 27, 2010Three 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 frontViewpointSaturday, February 27, 2010Three 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 frontSaturday, February 27, 2010Volume 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 cellSaturday, February 27, 2010Trilinear InterpolationTrilinear Interpolation• Interpolate to compute RGBA away from grid• Nearest neighbor yields blocky images• Use trilinear interpolation• 3D generalization of bilinear interpolationNearestneighborTrilinearinterpolationSaturday, February 27, 2010Trilinear InterpolationTrilinear InterpolationBilinear interpolationTrilinear interpolationSaturday, February 27, 2010Three 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 frontSaturday, February 27, 2010Three 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 frontSaturday, February 27, 2010SplattingSplatting• 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)Saturday, February 27, 2010ExampleSaturday, February 27, 2010Three Options•Ray Casting•Splatting•3D
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