1. Slides prepared on 09 September, 2018
Exploiting occlusion to image hidden scenes
Christos Thrampoulidis
joint work with
G. Shulkind, F. Xu, W. Freeman, J H. Shapiro, A. Torralba, F. Wong, and G. Wornell
Reference:
“Exploiting occlusion in non-line-of-sight active imaging”, C.T. , G. Shulkind, F. Xu, W. Freeman, J H. Shapiro, A. Torralba, F. NC. Wong, and G. W Wornell. IEEE Transactions on Computational Imaging, 2018.
Slides prepared on 09 September, 2018

2. Seeing around the corner
Conventional imaging
Lens: (physically) maps each scene element x0,i to a distinct pixel value yi on the sensor
sensor
Seeing around the corner
visible (diffuse) wall
Applications: defense, search & rescue, robotic vision, autonomous vehicles, …

3. Challenges Conventional imaging Seeing around the corner
Lens: (physically) maps each scene element x0,i to a distinct pixel value yi on the sensor
sensor
Seeing around the corner
visible diffuse wall
Challenges
Measurements linear but uninformative:
very weak signal
sensor

4. Active NLOS imaging Challenge: Weak signal
Solution: Probe the scene with an active light source
sensor
laser
Challenge: Uninformative measurements
Previous approach:
Ultrafast time-of-flight measurements
[Velten et al. ’12; Buttafava et al. ‘15; Klein et al. ’16, …]

5. Active NLOS imaging Challenge: Weak signal
Solution: Probe the scene with an active light source
laser
sensor
Challenge: Uninformative measurements
Previous approach:
Ultrafast time-of-flight information
Drawbacks:
expensive and sensitive camera
extremely fast laser
slow: very long-acquisition times
The curse of light speed!
[Velten et al. ’12; Buttafava et al. ‘15; Klein et al. ’16, …]

6. Opportunistic NLoS imaging
Question: Can we see in a hidden room without ultrafast ToF measurements?
What are additional structural features that we can exploit?
Our Idea: Opportunistically exploit visible occluders
visible occluders
visible diffuse wall

7. Opportunistic NLoS imaging
Question: Can we see in a hidden room without ultrafast ToF measurements?
Our idea: Opportunistically exploit visible occluders
laser

8. Opportunistic NLoS imaging
Question: Can we see in a hidden room without ultrafast ToF measurements?
Our idea: Opportunistically exploit visible occluders
Occlusions create diversity .
laser

9. NLoS in action Computational method: Raw photon counts visible wall
hidden
pattern
Occluder
Image
structure
Computational method:
Binomial likelihood (Photon-efficient)
[Thrampoulidis,Shulkind,Xu,Freeman,Shapiro,Torralba,Wong,Wornell, IEEE Trans. Comp. Imaging, 2018]
[Xu*, Thrampoulidis*,Shulkind*,Shapiro,Torralba,Wong,Wornell, Optics Express, 2018]

10. More examples

11. Modeling gains VS ~ 70 PPP ~ 1100 PPP Photons Per Pixel (PPP) 40 min
Binomial likelihood VS
Gaussian likelihood ~
70 PPP
2.5 min ~
1100 PPP
40 min
Photons Per Pixel (PPP)