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- 1. Multi-Resolution Screen-Space Ambient Occlusion<br />Thai-Duong Hoang<br />Kok-Lim Low<br />National University of Singapore<br />1<br />
- 2. Ambient Occlusion (AO)<br />π©<br />Β <br />πͺ<br />Β <br />2<br />
- 3. AO<br />Cosine-weightedfraction of a tangent hemisphere that is occluded<br />πͺi<br />Β <br />π§<br />Β <br />π½π<br />Β <br />π π<br />Β <br />π©<br />Β <br />ππππ₯<br />Β <br />π΄ππ©=1πΞ©ππ©,ππcosππππ€π<br />Β <br />ππβ₯ππππ₯:π=0ππ=0Β Β Β Β Β Β Β Β : π=1<br />Β <br />3<br />
- 4. Screen-Space AO (SSAO)<br />π©<br />Β <br />Volumetric AO [SKUT10]<br />4<br />
- 5. SSAO(Dis)Advantages<br />Inaccurate<br />Local AO<br />Over/underestimated AO<br />Low quality<br />Noise<br />Blur<br />Simple<br />Fast<br />General<br />Easy to integrate<br />5<br />
- 6. Multi-Resolution AO (MSSAO)Intuition<br />π΄π2<br />Β <br />π΄π1<br />Β <br />π΄π3<br />Β <br />π΄ππππππ=maxπ΄ππ<br />Β <br />6<br />
- 7. Multi-Resolution AO (MSSAO)Intuition<br />256x256<br />π΄π256<br />Β <br />512x512<br />π΄π512<br />Β <br />1024x1024<br />π΄π1024<br />Β <br />π΄ππππππ=fmaxπ΄ππ,Β averageπ΄πππ΄ππππππβ₯maxπ΄πππ΄ππππππβaverageπ΄ππ<br />Β <br />7<br />
- 8. MSSAOOverview<br />Geometry<br />g-buffer (1024x1024)<br />Downsample<br />Compute AO<br />(256x256)<br />AO buffer (256x256)<br />g-buffer (256x256)<br />Blur & Upsample<br />g-buffer (512x512)<br />Compute AO<br />(512x512)<br />AO buffer (512x512)<br />Blur & Upsample<br />Compute AO<br />(1024x1024)<br />g-buffer (1024x1024)<br />AO buffer (1024x1024)<br />8<br />
- 9. MSSAOAO from Multiple Resolutions<br />9<br />
- 10. MSSAOOverview<br />Geometry<br />g-buffer (1024x1024)<br />Downsample<br />Compute AO<br />(256x256)<br />AO buffer (256x256)<br />g-buffer (256x256)<br />Blur & Upsample<br />g-buffer (512x512)<br />Compute AO<br />(512x512)<br />AO buffer (512x512)<br />Blur & Upsample<br />Compute AO<br />(1024x1024)<br />g-buffer (1024x1024)<br />AO buffer (1024x1024)<br />10<br />
- 11. MSSAODownsampling<br />π©1π§β€π©2π§β€π©3π§β€π©4π§<br />ifπ©4π§βπ©1π§β€ππ‘hπππ hπππ<br />π©β(π©2+π©3)/2π§β(π§2+π§3)/2<br />else<br />π©βπ©2π§βπ§2<br />Β <br />π1<br />Β <br />π2<br />Β <br />π<br />Β <br />π3<br />Β <br />π4<br />Β <br />11<br />
- 12. MSSAOOverview<br />Geometry<br />g-buffer (1024x1024)<br />Downsample<br />Compute AO<br />(256x256)<br />AO buffer (256x256)<br />g-buffer (256x256)<br />Blur & Upsample<br />g-buffer (512x512)<br />Compute AO<br />(512x512)<br />AO buffer (512x512)<br />Blur & Upsample<br />Compute AO<br />(1024x1024)<br />g-buffer (1024x1024)<br />AO buffer (1024x1024)<br />12<br />
- 13. MSSAONeighborhood Sampling<br /><ul><li>Project the AO radius of influence to screen space at each pixel π at resolution π ππ π to get ππ(π) (in terms of pixels)
- 14. Cap πππ to some value ππππ₯ (typical value is 5)</li></ul>Β <br />1024x1024<br />16-point Poisson disk<br />512x512<br />256x256<br />Works well with a 3x3 Gaussian filter<br />13<br />
- 15. MSSAOComputing AO<br />Low-variance<br />Cheap<br />Biased<br />πͺi<br />Β <br />π§<br />Β <br />π½π<br />Β <br />π π<br />Β <br />π©<br />Β <br />π΄π(π©)=1ππ=1ππ(π©,ππ)(π§βπͺπβπ©)Β <br />model after the Monte-Carlo approximation of<br />π΄ππ©=1πΞ©ππ©,ππcosπππππ<br />Β <br />14<br />
- 16. MSSAOOverview<br />Geometry<br />g-buffer (1024x1024)<br />Downsample<br />Compute AO<br />(256x256)<br />AO buffer (256x256)<br />g-buffer (256x256)<br />Blur & Upsample<br />g-buffer (512x512)<br />Compute AO<br />(512x512)<br />AO buffer (512x512)<br />Blur & Upsample<br />Compute AO<br />(1024x1024)<br />g-buffer (1024x1024)<br />AO buffer (1024x1024)<br />15<br />
- 17. MSSAOBilateral Upsampling<br />Bilinear weightsΒ π€π<br />Depth weights<br />π€π§ππ=11+π§πβπ§π‘π§<br />Normal weights<br />π€πππ=π§βπ§ππ‘π<br />Β <br />916<br />Β <br />316<br />Β <br />316<br />Β <br />116<br />Β <br />π΄ππ=π=14π€ππππ€π§πππ€ππππ΄πππ<br />Β <br />16<br />
- 18. MSSAOCombining AO Values<br />π΄ππππππ=1β1βmaxπ΄ππ1βavgπ΄ππ<br />maxπ΄ππand avgπ΄ππare computed by βpropagatingβ appropriate values across resolutions<br />Avoid underestimating AO by ensuringπ΄ππππππβ₯maxπ΄ππ<br />And a plausible heuristicπ΄ππππππβavgπ΄ππ<br />Β <br />17<br />
- 19. MSSAOTemporal Filtering<br />π=0.5<br />Β <br />π=0<br />Β <br />π΄πππ’ππ=πΒ π΄πππππ£+1βππ΄ππππππ<br />Β <br />π=0<br />Β <br />18<br />
- 20. ResultsQuality<br />Blizzard [FM08]<br />MSSAO<br />19<br />
- 21. ResultsQuality<br />HBAO [BSD08]<br />MSSAO<br />20<br />
- 22. ResultsQuality<br />MSSAO<br />VAO [SKUT10]<br />21<br />
- 23. ResultsGround-truth Comparison<br />22<br />MSSAO<br />Blender<br />
- 24. ResultsNoise/Blur<br />MSSAO<br />HBAO [BSD08]<br />Blizzard [FM08]<br />23<br />
- 25. ResultsMultiple AO Scales<br />Small AO radius<br />MSSAO<br />Large AO radius<br />24<br />
- 26. ResultsPerformance<br /><ul><li>Scenes rendered at 1024x1024 on GeForce GTX 460M
- 27. Exclusive of geometry pass
- 28. The same parameters used to produce the shown images</li></ul>25<br />
- 29. MSSAOConclusions<br />Inaccurate<br />Local AO<br />Over/underestimated AO<br />Low quality<br />Noise<br />Blur<br />Use more memory<br />Poor temporal coherence on very thin geometry<br />Not too noticeable<br />Errors due to the use of coarse resolutions<br />Not too noticeable unless compared with ground-truths<br />Simple<br />Fast<br />General<br />Easy to integrate<br />Capture multiple shadow frequencies<br />26<br />
- 30. ResultsAdditional Results<br />27<br />
- 31. ResultsAdditional Results<br />28<br />
- 32. ResultsAdditional Results<br />29<br />
- 33. ResultsAdditional Results<br />30<br />
- 34. Thank You<br />31<br />

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