1. Attenuating Natural Flicker Patterns Yoav Y. Schechner Nir Karpel Support: Taub Foundation, Ollendorff Foundation (BMBF), ISF Ack: Yoav Fhiler, Naftali Blau, Nir Geva Dept. Elect. Eng. Technion – Israel Institute of Technology

2. Spatio-Temporal Illumination Patterns Y. Schechner & N. Karpel, Attenuating flicker Spatially nonuniform illumination Temporally varying illuminaton May disrupt computer-vision

3. Spatio-Temporal Patterns Y. Schechner & N. Karpel, Attenuating flicker Spatiotemporal pattern = Caustic networks = Flicker

4. Dependency on Depth: Normalized-Amplitude Y. Schechner & N. Karpel, Attenuating flicker strong flicker at shallow depths strong flicker when very deep Walker 1994 Marine Light Field Statistics

5. Y. Schechner & N. Karpel, Attenuating flicker Dependency on Depth: Temporal Frequency z z 1  max ~ Walker 1994 Marine Light Field Statistics

6.  max  Intensity 1 Hz2 Hz3 Hz Broadband Temporal Spectrum Conclusion: Need seconds to average out flicker Walker 1994 Marine Light Field Statistics

7. z 1 What Do We Want? we need seconds to average out flicker but for video… we want O ( 0.1 sec ) to eliminate flicker linear method nonlinear method Y. Schechner & N. Karpel, Attenuating flicker

8. Failure of Trivial Methods Raw frames Y. Schechner & N. Karpel, Attenuating flicker

9. spatial derivative temporal median integration Weiss 2001 Matsushita et. al. 2002 Shadow Removal in Open Air median of derivative

10. Hypothesis: A similar method can be applied to handle underwater flicker Distinguishing aspects DC (mean energy) value: implication to color Very frequent changes (spatially and temporally) Gradual changes (spatially and temporally) Veiling light (not multiplicative)

11. Spatio-Temporal Patterns Y. Schechner & N. Karpel, Attenuating flicker Raw frames Flicker-removed

12. Spatio-Temporal Patterns Flicker-removed Raw frames Y. Schechner & N. Karpel, Attenuating flicker

13. Not a Final Word Stabilize illumination This is heuristic. …Place for better sophistication? Yoav Schechner & Nir Karpel