1. Simple and Robust Iterative Importance Sampling of Virtual Point Lights
Iliyan Georgiev
Philipp Slusallek

2. Motivation Instant Radiosity (IR) – two-pass Previous approaches
Cheap pre-processing
Expensive rendering
Previous approaches
Bidirectional Instant Radiosity [Segovia et al. 06]
Metropolis Instant Radiosity [Segovia et al. 07]
Difficult to implement
Multiple sampling strategies
Many parameters
Stratification problems
“One-pixel image” assumption
November 22, 2018

3. Our Method Simple extension of IR Probabilistically accept VPLs
Generate VPLs from light sources only
Probabilistically accept VPLs
Proportionally to total contribution
All VPLs bring the same power to the image
“One-pixel image” assumption
Minimum importance storage
Filter VPLs on the fly
November 22, 2018

4. Probabilistic VPL Acceptance
VPL energy
𝐿 𝑖 = 𝐿 𝑖 𝑝 𝑖 𝑝 𝑖 = 𝐿 𝑖 𝑝 𝑖 𝜒 0, 𝑝 𝑖 𝑡 𝑑𝑡
One-sample Monte Carlo integration with 𝜉
𝐿 𝑖 = 𝐿 𝑖 𝑝 𝑖 , 𝜉< 𝑝 𝑖 &0, else
Allows to control VPL density
November 22, 2018

5. Importance Sampling Want 𝑁 VPLs with equal total image contribution
Φ 𝑣 = Φ 𝑁
For each VPL candidate 𝑖 with energy 𝐿 𝑖
Estimate total image contribution Φ 𝑖
Russian roulette decision with 𝑝 𝑖 =min Φ 𝑖 Φ 𝑣 +𝜀,1
Accept with energy 𝐿 𝑖 𝑝 𝑖
Discard
See paper for details
November 22, 2018

6. Estimating Image Contribution
Computing Φ 𝑖
Cast a number of camera rays
Connect VPLs to camera points to estimate Φ 𝑖
Camera points – analog of importons
Computing Φ 𝑣
Iteratively
Start with Φ 𝑣 =0
Loop
Render frame
Accumulate Φ 𝑣
Single pass – path tracing, using VPLs, etc.
November 22, 2018

7. Our Extension (0.07 acceptance)
Results
Instant Radiosity
Our Extension (0.07 acceptance)
November 22, 2018

8. Average acceptance probability: 0.28
Results
Average acceptance probability: 0.28
November 22, 2018

9. Average acceptance probability: 0.23
Results
Average acceptance probability: 0.23
November 22, 2018

10. Wrap Up Simple extension of IR
Generate VPLs from light sources only
Probabilistically accept VPLs on the fly
No additional storage
Easy to parallelize
Few parameters
“One-pixel image” assumption
November 22, 2018

11. Iliyan Georgiev