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Multi-Resolution Screen-Space Ambient Occlusion

Multi-Resolution Screen-Space Ambient Occlusion. Thai-Duong Hoang Kok -Lim Low. National University of Singapore. Ambient Occlusion (AO). AO. Cosine-weighted fraction of a tangent hemisphere that is occluded. :. Screen-Space AO (SSAO). Volumetric AO [SKUT10]. SSAO (Dis)Advantages.

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Multi-Resolution Screen-Space Ambient Occlusion

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  1. Multi-Resolution Screen-Space Ambient Occlusion Thai-Duong Hoang Kok-Lim Low National University of Singapore

  2. Ambient Occlusion (AO)

  3. AO Cosine-weightedfraction of a tangent hemisphere that is occluded :

  4. Screen-Space AO (SSAO) Volumetric AO [SKUT10]

  5. SSAO(Dis)Advantages • Inaccurate • Local AO • Over/underestimated AO • Low quality • Noise • Blur • Simple • Fast • General • Easy to integrate

  6. Multi-Resolution AO (MSSAO)Intuition

  7. Multi-Resolution AO (MSSAO)Intuition 256x256 512x512 1024x1024

  8. MSSAOOverview Geometry g-buffer (1024x1024) Downsample AO buffer (256x256) Compute AO (256x256) g-buffer (256x256) Blur & Upsample AO buffer (512x512) Compute AO (512x512) g-buffer (512x512) Blur & Upsample AO buffer (1024x1024) Compute AO (1024x1024) g-buffer (1024x1024)

  9. MSSAOAO from Multiple Resolutions

  10. MSSAOOverview Geometry g-buffer (1024x1024) Downsample AO buffer (256x256) Compute AO (256x256) g-buffer (256x256) Blur & Upsample AO buffer (512x512) Compute AO (512x512) g-buffer (512x512) Blur & Upsample AO buffer (1024x1024) Compute AO (1024x1024) g-buffer (1024x1024)

  11. MSSAODownsampling if else

  12. MSSAOOverview Geometry g-buffer (1024x1024) Downsample AO buffer (256x256) Compute AO (256x256) g-buffer (256x256) Blur & Upsample AO buffer (512x512) Compute AO (512x512) g-buffer (512x512) Blur & Upsample AO buffer (1024x1024) Compute AO (1024x1024) g-buffer (1024x1024)

  13. MSSAONeighborhood Sampling • Project the AO radius of influence to screen space at each pixel at resolution to get (in terms of pixels) • Cap to some value (typical value is 5) 1024x1024 16-point Poisson disk 512x512 256x256 Works well with a 3x3 Gaussian filter

  14. MSSAOComputing AO model after the Monte-Carlo approximation of • Low-variance • Cheap • Biased

  15. MSSAOOverview Geometry g-buffer (1024x1024) Downsample AO buffer (256x256) Compute AO (256x256) g-buffer (256x256) Blur & Upsample AO buffer (512x512) Compute AO (512x512) g-buffer (512x512) Blur & Upsample AO buffer (1024x1024) Compute AO (1024x1024) g-buffer (1024x1024)

  16. MSSAOBilateral Upsampling • Bilinear weights • Depth weights • Normal weights

  17. MSSAOCombining AO Values • and are computed by “propagating” appropriate values across resolutions • Avoid underestimating AO by ensuring • And a plausible heuristic

  18. MSSAOTemporal Filtering

  19. ResultsQuality Blizzard [FM08] MSSAO

  20. ResultsQuality HBAO [BSD08] MSSAO

  21. ResultsQuality MSSAO VAO [SKUT10]

  22. ResultsGround-truth Comparison MSSAO Blender

  23. ResultsNoise/Blur MSSAO HBAO [BSD08] Blizzard [FM08]

  24. ResultsMultiple AO Scales Small AO radius Large AO radius MSSAO

  25. ResultsPerformance • Scenes rendered at 1024x1024 on GeForce GTX 460M • Exclusive of geometry pass • The same parameters used to produce the shown images

  26. MSSAOConclusions • Inaccurate • Local AO • Over/underestimated AO • Low quality • Noise • Blur • Use more memory • Poor temporal coherence on very thin geometry • Not too noticeable • Errors due to the use of coarse resolutions • Not too noticeable unless compared with ground-truths • Simple • Fast • General • Easy to integrate • Capture multiple shadow frequencies

  27. ResultsAdditional Results

  28. ResultsAdditional Results

  29. ResultsAdditional Results

  30. ResultsAdditional Results

  31. Thank You

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