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TUB @ MediaEval 2014 Visual Privacy Task: Reversible Scrambling on foreground masks
S. Schmiedeke, P. Kelm, L. Goldmann, T. Sikora Communication Systems Group | Imcube Labs GmbH
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TUB @ MediaEval 2014 Visual Privacy Task: Reversible Scrambling on Foreground Masks
• Motivation
• Method overview
• Experimental results
• Conclusion
Seite 2
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Motivation
TUB @ MediaEval 2014 Visual Privacy Task: Reversible Scrambling on Foreground MasksSeite 3
Color Histogramm DescriptorColor Histogramm Descriptor
Visual Distance
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Motivation
TUB @ MediaEval 2014 Visual Privacy Task: Reversible Scrambling on Foreground MasksSeite 4
revertible
Scrambling of foreground masks
Descrambling of foreground masks
Transmission/ Compression Error
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TUB @ MediaEval 2014 Visual Privacy Task: Reversible Scrambling on Foreground Masks
Method overview
Seite 5
Background modelling• Based on Gaussian-Mixture models (GMM)• Number of needed components is automatically detected
Region of interest: Foreground masks• Background subtraction• Erosion and morphological operations
Scrambling of ROI• Reversible shuffling of pixels within disjunct ROI areas
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TUB @ MediaEval 2014 Visual Privacy Task: Reversible Scrambling on Foreground Masks
Method overview
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• Simple and fast
• On-the-fly background modelling
• Parameter-free (except for global pixel threshold)
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TUB @ MediaEval 2014 Visual Privacy Task: Reversible Scrambling on Foreground Masks
Method overview
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• Robust to camera shaking
• Slight camera movements were• compensated by frame subsampling and by GMM
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TUB @ MediaEval 2014 Visual Privacy Task: Reversible Scrambling on Foreground Masks
Method overview
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• Scene information remains • visible to operator
• Events such as left-luggage, vandalism, emergency cases, etc. stay visible
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Method overview
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• Shapes of scrambled persons • allow basic scene understanding
• Actions such as fighting, mugging, etc. are still recognizable
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TUB @ MediaEval 2014 Visual Privacy Task: Reversible Scrambling on Foreground Masks
Experimental results
• Good privacy preservation (above median scores)
• Fair visual „appropriateness“ (near to median)
• Good Level of Intelligibility (near to median)
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Evaluation scores (median scores in brackets)
Stream 1 Stream 2 Stream 3
Intelligibility 73.6% (74.9%) 75.2% (79.3%) 66.5% (69.6%)
Privacy 59.0% (50.2%) 62.6% (46.5%) 60.7% (40.7%)
Pleasantness 21.9% (24.8%) 60.8% (69.6%) 58.1% (59.7%)
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Conclusion
11
• Good overall privacy level
• Good level of retention of ‘useful’ information
• Fast (real-time) and easy to implement
• Compression does not break recovering
scrambling
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Conclusion
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• Still room for improvement in background modelling
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Thank You! Questions?
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Backup
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TUB @ MediaEval 2014 Visual Privacy Task: Reversible Scrambling on Foreground Masks
Method overview
Seite 15
• Simple and fast
• Robust to camera shaking
• Scene information remains visible to operator
• Shapes of scrambled persons allow basic scene understanding (fighting, mugging, etc.)