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

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

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

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

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

Intensity Broadband Temporal Spectrum Walker 1994 Marine Light Field Statistics w 1 Hz 2 Intensity Broadband Temporal Spectrum Walker 1994 Marine Light Field Statistics w 1 Hz 2 Hz 3 Hz w max Conclusion: Need seconds to average out flicker

What Do We Want? 1 z we need seconds to average out flicker but What Do We Want? 1 z we need seconds to average out flicker but for video… we want O(0. 1 sec) linear method to eliminate flicker nonlinear method Y. Schechner & N. Karpel, Attenuating flicker

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

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

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

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

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

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