1. Real-time Global Illumination with precomputed probe
Baek Jun Kim
KAIST (Korea Advanced Institute of Science and Technology) 1

2. Review Ambient Occlusion Rendering with Neural Networks (20184230 김세훈)
1) Deep shading (2D frame based learning)
2) DRAO (3D geometry based learning)

3. Global Illumination Direct illumination only
Global illumination (indirect illumination)

4. Ray Tracing Ray Tracing In Real-time?
To implement Global Illumination
In Real-time?
Too costly to compute at interactive rates
Even several hours for a image
How to realize Real-time Ray Tracing
Precomputation
… and others

5. Papers
Real-Time Global Illumination using Precomputed Light Field Probes
Real-time Global Illumination by Precomputed Local Reconstruction from Sparse Radiance Probes

6. Real-Time Global Illumination using Precomputed Light Field Probes
Morgan McGuire, Michael Mara, Derek Nowrouzezahrai, and David Luebke.
In I3D

7. Summary Precomputing Probe Radiance, normal, and distance map
Ray casting using Probe
Intersection testing with distance map
Shading with Probes
1) Spatial-Temporal Radiance Denoising
(BRDF factorization)
2) Irradiance with Pre-Filtered Visibility
(Geometry aware)

8. Real-Time GI using Precomputed Light Field Probes
A scene computed in 42ms (212fps)
Let me show its previous works briefly:
Image Based Lighting
Voxel Cone Tracing

9. Image-based Lighting Cube map (Environment mapping)
In this paper, every probe get its cube map.

10. Voxel Cone Tracing Using Sparse Voxel Octree Optimized in modern GPU
Hierarchical

11. Precomputed Light Field Probes
Rasterization to render cube map
Octahedral parameterization for efficiency
Two-level MIPmap hierarchy (heuristic)

12. Light Field Probe Ray Tracing
How to use precomputed probe?
We can trace a ray!
Procedure
Selecting a probe
Single-probe tracing routine
Selecting fall-back probes

13. Selecting a Probe The probe whose center lies closest to the ray Ray

14. Single-probe tracing routine

15. Intersection test
Intersection test by comparing depth map value in the probe and radial distance from the probe’s center
Ray
Depth map in the probe
Surface
Probe

16. Intersection test (2)
If depth map value is smaller than radial distance, the ray has either hit a surface or pass behind the surface
Ray
Depth map in the probe
Surface
Probe

17. Intersection test (3)
By using normal map in probe, we can distinguish between HIT and behind the surface
Ray
Depth map in the probe
Surface
Probe

18. Selecting fall-back probes
If unable to find a definitive hit or miss, pick another probe

19. Shading with Light Field Probes
Now we can trace a ray with probes, then?
3 Global Illumination Algorithm
Compute indirect lighting using MC & Importance Sampling
Unbiased, but slow
We have to reduce the number of ray samples
Spatial-Temporal Radiance Denoising
Irradiance with Pre-Filtered Visibility

20. Spatial-Temporal Radiance Denoising
Factorize BRDF into Lambertian term and Glossy Term
Indirect illumination pass traces one ray sampled from each of them and writes the result to each buffer
For Lambertian reflection, we compute incident irradiance instead of radiance

21. Spatial-Temporal Radiance Denoising (2)
Lambertian reflections is spatially slower- varying
Use of wider filter
Glossy reflection is spatially faster-varying
Use of narrower filter

22. Irradiance with Pre-Filtered Visibility
How to compute irradiance?
Precompute irradiance map
Interpolate irradiance map at eight probes within the cube of the intersection
Reduce number of texture operation → really fast
Limitation: Lighting and darkness leaking

23. Irradiance with Pre-Filtered Visibility (2)
Geometry-aware approach
While precomputing irradiance map, we also compute radial distance map
At runtime, we use the radial distance map for interpolating irradiance

24. Summary Precomputing Probe Radiance, normal, and distance map
Ray casting using Probe
Intersection testing with distance map
Shading with Probes
1) Spatial-Temporal Radiance Denoising
(BRDF factorization)
2) Irradiance with Pre-Filtered Visibility
(Geometry aware)

25. Real-Time Global Illumination using Precomputed Light Field Probes
Ari Silvennoinen and Jaakko Lehtinen.
ACM Transactions on Graphics, November 2017.

26. Summary To get indirect illumination, combined two methods
Precomputed Light Transport
Interpolation
Factorize Global Transport into (1) Local Transport and (2) Probe Transport

27. Real-time GI by Precomputed Local Reconstruction from Sparse Radiance Probes
GI = Direct illumination + Indirect illumination
How to get indirect illumination?

28. How to get indirect illumination?
In this paper,
Precomputed light transport
Direct-to-Indirect transfer [Hašan et al ]
Interpolation method
Interpolated irradiance and bandlimited radiance [E.g. Ward 1992]

29. Direct-to-Indirect transfer [Hašan et al. 2006]
Precomputed radiance transfer method
Precompute transfer matrix that map direct illumination into indirect illumination

30. Interpolation method Interpolation from radiance probes
are spatial interpolation weight ω p2 p1 x

31. Limitations
a) Direction mismatch
b) Visibility mismatch

32. Visibility-Aware Interpolation
Ψ for direction
Vi(ω) for Visibility

33. Spherical harmonics is a kind of Laplace transform of Sphere
Probe Radiance
High-resolution angular sampling of the probes’ radiance is expensive
Replace it by Spherical Harmonics form
λ: probe radiance vector
Y: SH basis function (basis func. index j)
Spherical harmonics is a kind of Laplace transform of Sphere

34. Local transport Operator
Local transport Operator transforms the probe radiance vector λ to interpolated incident radiance at x as a function of the continuous direction ω

35. Precomputed Transport
transport coefficients ϕij

36. Factorized transport
Factorize global transport into local transport and probe transport
Interpolate with probes

37. Local Transport
Precomputed local transport matrix: accounts for near field effects between the receiver and the mutually visible surfaces seen by the probes
Vi(ω) makes matrix

38. Probe Transport
Captures radiance in a sparse set of probes at runtime

39. Scene Example

40. Scene Exmaple (2)

41. Implementation - Precomputation
Probe locations and radii:
Every surface point is under the support of at least one probe
Every surface point is visible from at least one probe
Use greedy algorithm
Cluster Receivers into a vector

42. Implementation - Runtime
Computing Probe Transport
Direct illumination light map is updated every frame

43. Result

44. Result

45. Summary To get indirect illumination, combined two methods
Precomputed Light Transport
Interpolation
Factorize Global Transport into (1) Local Transport and (2) Probe Transport

46. Pros and Cons
Real-Time Global Illumination using Precomputed Light Field Probes
Dynamic Camera
Static and Dynamic Environment
Real-time Global Illumination by Precomputed Local Reconstruction from Sparse Radiance Probes
Only Static Environment
Dynamic Light Source

47. Quiz
In Real-Time Global Illumination using Precomputed Light Field Probes, which map of the probe used to test intersection during Light Field Probe Ray Tracing?
(1) Shadow map (2) Distance map
(3) Irradiance map (4) Radiance map
In Real-time Global Illumination by Precomputed Local Reconstruction from Sparse Radiance Probes, global transport is factorized into 2 parts: precomputed ( ) transport and ( ) transport which is computed at runtime
(1) probe, local (2) local, probe
(3) SH, SVD (4) SVD, SH