attenuating natural flicker patterns yoav y. schechner nir karpel support: taub foundation,...

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

Spatio-Temporal Illumination Patterns

Y. Schechner & N. Karpel, Attenuating flicker

• Spatially nonuniform illumination• Temporally varying illuminaton• May disrupt computer-vision

Spatio-Temporal Patterns


Spatiotemporal pattern = Caustic networks = Flicker

Dependency on Depth: Normalized-Amplitude


strong flicker at shallow depths

strong flicker when very deep

Walker 1994

Marine Light Field Statistics


Dependency on Depth: Temporal Frequency

z

z

1max ~

Walker 1994


max

Inte

nsity

1 Hz 2 Hz 3 Hz

Broadband Temporal Spectrum

Conclusion: Need seconds to average out flicker

Walker 1994


z

1What 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


Failure of Trivial Methods

Raw frames


spatial derivative

temporal median

integration

Weiss 2001Matsushita et. al. 2002

Shadow Removal in Open Air

median of derivative

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)



Raw frames

Flicker-removed


Flicker-removed

Raw frames


Not a Final Word

Stabilize illumination

This is heuristic.

…Place for better sophistication?

Yoav Schechner & Nir Karpel

attenuating natural flicker patterns yoav y. schechner nir karpel support: taub foundation,...

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