unified crowd segmentation
DESCRIPTION
Unified Crowd Segmentation. P . Tu , T. Sebastian, G. Doreto , N. Krahnstoever , J. Rittscher , T. Yu ECCV 2008. Presenter: Ramin Mehran. Goal: Segmentation. Crowd Analysis Conventional Approach Segmentation Object Detection Tracking Analysis. Ideas: a Robust Algorithm. Approaches. - PowerPoint PPT PresentationTRANSCRIPT
P. TU, T. SEBASTIAN, G . DORETO, N. KRAHNSTOEVER , J . R ITTSCHER , T. YU
ECCV 2008
Unified Crowd Segmentation
Presenter: Ramin Mehran
2
Goal: Segmentation
10/2/2008CV Lab @ UCF - Presenter: Ramin Mehran
Crowd Analysis Conventional Approach
Segmentation Object Detection Tracking Analysis
3
Ideas: a Robust Algorithm
Partial Occlusion
Dynamic Background
Foreground Clutter
10/2/2008CV Lab @ UCF - Presenter: Ramin Mehran
CV Lab @ UCF - Presenter: Ramin Mehran
4
Approaches
10/2/2008
Bottom up Low level feature grouping Whole body classifiers
Top down Background segmentation
BOTH!
CV Lab @ UCF - Presenter: Ramin Mehran
5
Algorithm Overview
Head-Shoulder Detection
Assigning Patches to
Heads
Grouping Patches
E-Step (assignment
update)
M-Step (consistency
check)
10/2/2008
CV Lab @ UCF - Presenter: Ramin Mehran
6
Affinity of Patches to Hypotheses
10/2/2008
Ck
zj
zi
gk(zi)
gk(zi, zj)•Top Down Head/Shoulder
Detection•Bottom up Patch Affinities
Ck Hypothesis
Head/Shoulder
Background
Head-Shoulder Detection
Assigning Patches to
Heads
Grouping Patches
CV Lab @ UCF - Presenter: Ramin Mehran
7
Maximum Likelihood
10/2/2008
How likely is the assignment a patch to a head
E-M Steps
Is it likely near the head? Is it like neighboring patches?
Consistency
Assignment
indicatorAffinit
y
CV Lab @ UCF - Presenter: Ramin Mehran
8
E-Step
10/2/2008
V
XZVLVp );|()(
)Hypotheses ,(Patch kiP
V
k
iVVIncrease the expectations
CV Lab @ UCF - Presenter: Ramin Mehran
9
E-Step affect
10/2/2008
CV Lab @ UCF - Presenter: Ramin Mehran
10
M-Step
10/2/2008
Enforce Consistency Where is the head? Contiguous patches
Path from Patches to the Head Dynamic Programming Shortest low cost path
Ck
Cm
Inconsistent patches
No Contribution to V (assignment)
CV Lab @ UCF - Presenter: Ramin Mehran
11
Head/Shoulder Body Detection
10/2/2008
Strong Classifier out of Weak Classifiers
Strong Classifier (SC(s,z))Orientatio
nOrientatio
nOrientatio
nOrientatio
n
Aggregation of weak Classifiers
CV Lab @ UCF - Presenter: Ramin Mehran
12
Weak Classifier
10/2/2008
Weak Classifier Ratio of the intersection of
patch and the region Sobel Orientation
Ck
zi
R
Needs Camera
Calibration
CV Lab @ UCF - Presenter: Ramin Mehran
13
What’s the Affinity?
10/2/2008
Patch to Head/Shoulder Affinity
Patch to Patch Affinity Histogram matching of
colors Motion matching of
flow
),()( ikik zssczg
Head and body bounding box
patch
),(),( jijik zzsimzzg
CV Lab @ UCF - Presenter: Ramin Mehran
14
Patch Size
10/2/2008
Camera CalibrationWidth of the average pedestrianLarge Patches
Occlusion HandlingSmall Patches
Discrimination of correct and incorrect assigments
CV Lab @ UCF - Presenter: Ramin Mehran
15
Sample Results
10/2/2008
CV Lab @ UCF - Presenter: Ramin Mehran
16
Results
10/2/2008
Compared to Histogram of Oriented Gradient method
Superior mostly because of handling occlusions
CV Lab @ UCF - Presenter: Ramin Mehran
17
Thank you!
10/2/2008