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Combining Edges and Points for Interactive High-Quality Rendering
Kavita Bala Bruce Walter Donald Greenberg Cornell University
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Motivation Goal: Interactive high-quality rendering
Expensive shading: e.g., global illumination But, mostly smooth (coherent) naïve reconstruction points
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Edge-and-Point Rendering
Edges: important discontinuities Silhouettes and shadows Points: sparse shading samples points edges edge-and-point reconstruction
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Edge-and-Point Image Alternative display representation
Edge-constrained interpolation preserves sharp features Fast anti-aliasing EPI naive
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EPI Properties Works directly with edges and points
No meshing Image-space display representation: limited sub-pixel precision Approximate edges and points Scales to complex objects
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Edge-constrained interpolation
System Edge finding 3D edges Point cache 3D points Shader Asynchronous Request samples Shading 2D edges Rasterization Reprojection 2D points Edge-constrained interpolation Exploits temporal coherence Decouples shading from display EPI
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Related Work Sparse sampling and reconstruction Fast ray tracing
[Bala99,Guo98,Pighin97,Simmons00,Stamminger00,Tole02,Wald02,Walter99] Fast ray tracing [Parker99,Purcell02,Wald01] Display representation [Levoy86,Pfister00,Rusinkiewicz00,Zwicker01] Edge finding Discontinuity meshing [Heckbert92,Lischinski92] Event finding [Duguet02,Durand99] [Johnson01,Sander00,Sander01]
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Pixel types Pixels can have arbitrary edge complexity
Classify pixels into 3 groups Empty: no edges Simple: can be approximated by 1 edge Complex: everything else Typical pixel classification statistics empty (85-95%), simple (4-10%), complex (1-4%) Empty Simple Complex
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Edge-and-Point Image (EPI)
Goal: compact and fast Store at most one edge and one point per pixel Limited sub-pixel precision Combine edges and points in image space View-driven, lazy evaluation Point sample (shaded) Edge EPI pixel
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Edge Reconstruction Rasterize edges onto image plane
Record their intersections with pixel boundaries Classify pixels and reconstruct simple edges Discontinuity Edges Rasterization Reconstruction empty simple complex pixel boundary intersection
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Reachability Reachable samples Propagated outward from each pixel
Pixel’s 5x5 neighborhood Connected without crossing any edges (or complex pixels) Propagated outward from each pixel Reachable Unreachable Propagation
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Interpolation Interpolate a color for each pixel
Uses 5x5 weighted kernel Only interpolate from reachable samples Empty
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Interpolation Interpolate a color for each pixel
Uses 5x5 weighted kernel Only interpolate from reachable samples Simple pixels: pick one side of edge Empty Simple
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Interpolation Interpolate a color for each pixel
Uses 5x5 weighted kernel Only interpolate from reachable samples Simple pixels: pick one side of edge Complex pixels: ignore reachability Empty Simple Complex
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Anti-Aliasing Interpolation computes one color per pixel
Result has classic “staircase” aliasing Use edge information at simple pixels to blend between neighboring pixels Fast table-driven filter Cheap and effective After interpolation After anti-aliasing
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Anti-aliasing Magnified view of a ray traced image with 1 sample per pixel Magnified view of our results Our result using <1 sample per pixel Edges
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Complex Pixel Filter Can subdivide complex pixels in four
Many quadrants are empty or simple Extra work only at complex pixels Complex pixel Before After
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Point Sampling Point sample handling
Based on the Render Cache [Walter99,02] Produced by asynchronous shaders Stored in a fixed size point cache Project points onto current image plane Request new samples based on feedback
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Edge Finding: Types Silhouettes Shadows: hard and soft eye object
point light source shadow event blocker receiver area light source umbral event penumbral event blocker receiver
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Edge Finding Hierarchical trees: fast edge finding Interval-based
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Red: umbral edges, Blue: penumbral edges
Soft Shadow Edges Black: silhouettes, Red: umbral edges, Blue: penumbral edges
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Reachability & interpolation
Putting it Together Edge finding 3D edges Point cache 3D points 2D edges Edge rasterization & reconstruction 2D points Reprojection EPI image Reachability & interpolation Anti-aliasing Complex pixel filter Finished frame
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Results: Quality Global illumination 3 lights 150k polygons
Without Edges With Edges
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Video
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Results Framerate: 8-14 fps Sparseness: 1-2%
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Summary EPI: New display representation
Combines edges and points Image-space: no meshing Compact EPI optimizes for common case Scales to complex scenes Fast anti-aliasing Fast, hierarchical edge finding for silhouettes and shadows
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Conclusion Combines best of edges and points
Decouple display from shading Arbitrary slow shaders Exploit coherence Spatial: interpolation Temporal: reprojection Software implementation GPU
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Acknowledgments Sebastian Fernandez
Everybody at the Program of Computer Graphics Stanford’s Digital Michelangelo Project Georgia Tech’s Large Geometric Model Archive NSF Intel
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Questions?
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Edge-and-Point Image Alternative display representation
Edge-constrained interpolation preserves sharp features Fast anti-aliasing
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