Motion Segmentation

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Motion Segmentation

• CAGDCG Seminar
• Wanqiang Shen
• 2008-04-09

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Application
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Motion analysis
Motion segmentation
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Problem

• Accurate
• Robust
• Fast

How much
What
How
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Traditional model

• A rigid-body motion

• Multiple rigid-body motions

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Paper

• 1 R. Vidal, Y. Ma, and S. Sastry. Generalized
  Principal Component Analysis (GPCA). IEEE
  Transactions on Pattern Analysis and Machine
  Intelligence, 27(12)115, 2005.
• 2 J. Yan and M. Pollefeys. A general framework
  for motion segmentation Independent,
  articulated, rigid, non-rigid, degenerate and
  non-degenerate. In European Conference on
  Computer Vision, pages 94106, 2006.
• 3 R. Tron and R. Vidal A Benchmark for the
  Comparison of 3-D Motion Segmentation Algorithms.
  IEEE International Conference on Computer Vision
  and Pattern Recognition, 2007.

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1 GPCA
Model
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1 Model
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1 Estimating n
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1 Estimating subspaces

• calculating normalized C
• Factorization
• Solving for the last 2 entries of each bi
• Solving for the first K-2 entries of each bi

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1 Optimizing clustering
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1 example
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1 Remarks

• Advantages
• Algebraic algorithm
• Dealing with both independent and dependent
  motions
• disadvantages
• Deteriorating as n increases
• C is sensitive to outliers

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2 LSA
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2 Projection
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2 Local subspace estimation
Affinity matrix
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2 Clustering

• Estimation N
• While Numofclusterslt N
• Compute affinity matrix for each clusters
• Divide each cluster into two clusters
• Evaluate the best subdivision

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2 examples
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2 Remarks

• Advantages
• Outliers are likely to be rejected
• Need less point trajectories
• disadvantages
• Neighbors of a point belong to different subspace
• The select neighbors may not span the underlying
  subspace

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3 test samples
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3 Benchmark
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3 comparing data

• Two groups

accuracy GPCA LSA
Check. 6.09 5.71
Traffic 1. 41 3.75
Articul. 2.88 4.38
All 4.59 5.09
time GPCA LSA
Check. 353ms 7.762s
Traffic 288ms 6.787s
Articul. 224ms 4.002s
All 324ms 7.165s

• Three groups

accuracy GPCA LSA
Check. 31.95 18.09
Traffic 19.83 26.05
Articul. 16.85 15.18
All 28.66 19.51
time GPCA LSA
Check. 842ms 17.314s
Traffic 529ms 12.746s
Articul. 125ms 1.288s
All 738ms 15.485s
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Thank you!