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Many-light methods – Clamping & compensation Jaroslav Křivánek Charles University, Prague.

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Presentation on theme: "Many-light methods – Clamping & compensation Jaroslav Křivánek Charles University, Prague."— Presentation transcript:

1 Many-light methods – Clamping & compensation Jaroslav Křivánek Charles University, Prague

2 1.Generate VPLs 2 Instant radiosity 2.Render with VPLs

3 3 Clamping 1000 VPLs - no clamping missing energy 1000 VPLs - clampingreference (path tracing)

4 Clamping Compensation Kollig & Keller, MCQMC 2004

5 Clamping reduces variance but some energy is lost Find formula for the lost energy Compute the lost energy by selective path tracing 5 Idea path tracing compensation full solution clamping

6 6 Clamping x p VPL power VPL emission distribution (BRDF lobe at p – for a diffuse VPL can be folded into  ) Geometry term oo Visibility min{ c, }

7 Clamping evaluates this equation Can be written as 7 Formal derivation

8 Unbiased solution 8 What’s missing? Path tracing compensation of the clamped energy VPLs w/ clamping

9 Compensation faster than path tracing everything (many path terminated early) 9 Result path tracing compensation full solution clamping

10 10 Biased result with clamping

11 11 Unbiased result with compensation

12 Dealing with Glossy Transport

13 13 Ground truth 1,000 VPLs100,000 VPLs Instant radiosity with glossy surfaces

14 Effect of clamping 14

15 Virtual Spherical Lights Hašan, Křivánek & Bala, SIGGRAPH Asia 2009

16 Cosine-weighted BRDF lobe at the VPL location Emission distribution of a VPL 16 Glossy Diffuse

17 Glossy VPL emission: illumination spikes Common solution: Only diffuse BRDF at light location 17

18 Remaining spikes 18

19 Common solution: Clamp VPL contributions 19 Remaining spikes xx VPL contribution = VPL power. BRDF( x ). cos( x ). 1 / || p – x || 2 spike! p As || p – x || → 0, VSL contribution → ∞

20 Instant radiosity: The practical version 20 Clamping and diffuse-only VPLs: Illumination is lost!

21 Comparison 21 Clamped VPLs: Illumination loss Path tracing: Slow

22 Recall: Emission Distribution of a VPL 22 Spike!

23 What happens as #lights   ? 23 Spiky lights converge to a continuous function!

24 Idea: We want a “virtual area light” 24 Aggregate incoming illumination Aggregate outgoing illumination “Virtual area light” Problem: What if surface is not flat?

25 25 VPL to VSL x p l Non-zero radius (r) Ω Integration over non-zero solid angle

26 26 Light Contribution x p l Non-zero radius (r) Ω Integration over non-zero solid angle y

27 27 Light Contribution x p l Non-zero radius (r) Ω Integration over non-zero solid angle y Problem: Finding y requires ray-tracing

28 28 Simplifying Assumptions x p l Non-zero radius (r) Ω Integration over non-zero solid angle y Constant in Ω: –Visibility –Surface normal –Light BRDF Taken from p, the light location

29 29 Light Contribution Updated x p l Non-zero radius (r) Ω Integration over non-zero solid angle

30 30 Virtual Spherical Light All inputs taken from x and p –Local computation Same interface as any other light –Can be implemented in a GPU shader Visibility factored from the integration –Can use shadow maps

31 Matrix row-column sampling –Shadow mapping for visibility –VSL integral evaluated in a GPU shader Need more lights than in diffuse scenes 31 Implementation

32 Results: Kitchen Most of the scene lit indirectly Many materials glossy and anisotropic Clamped VPLs 34 sec (GPU) – 2000 lights New VSLs: 4 min 4 sec (GPU) – lights Path tracing: 316 hours (8 cores) 32

33 Results: Disney concert hall Curved walls with no diffuse component Standard VPLs cannot capture any reflection from walls Clamped VPLs: 22 sec (GPU) – 4000 lights New VSLs: 1 min 26 sec (GPU) – lights Path tracing: 30 hours (8 cores) 33

34 Results: Anisotropic tableau Difficult case Standard VPLs capture almost no indirect illumination Clamped VPLs: 32 sec (GPU) – 1000 lights New VSLs: 1 min 44 sec (GPU) – 5000 lights Path tracing: 2.2 hours (8 cores) 34

35 Limitations: Blurring VSLs can blur illumination Converges as number of lights increases 5,000 lights - blurred 35 1,000,000 lights - converged

36 Many-light methods do not deal well with glossy scenes –Artifacts or energy loss –Energy loss -> change of material perception Handling glossy effects with many-lights –Virtual Spherical Lights –[Davidovič et al. 2010] 36 Conclusions


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