View
5
Download
0
Category
Preview:
Citation preview
Helmut Grabner 1,3, Jan Sochman 2, Horst Bischof 1, Jiri Matas 2
Training Sequential On-line Boosting Classifiers for Visual Tracking
1Institute for Computer Graphics and Vision, Graz University of Technology, Austria2Center for Machine Perception, Czech Technical University, Prague3Computer Vision Laboratory, ETH Zurich, Switzerland
M. Grabner, H. Grabner and H Bischof. Real-time tracking with on-line feature selection. CVPR 2006.
2008/12/09 - ICPR, Tampa 2Helmut Grabner - Computer Vision Laboratory – ETH Zurich
Tracking Requirements
� Adaptivity
� Robustness� Robustness
� Generality
2008/12/09 - ICPR, Tampa 3Helmut Grabner - Computer Vision Laboratory – ETH Zurich
Agenda
� Introduction
� Tracking as Binary Classification� On-line Boosting for Feature Selection� On-line Boosting for Feature Selection
� Sequential On-line Boosting
� Experiments� Conclusion
4Helmut Grabner - Computer Vision Laboratory – ETH Zurich2008/12/09 - ICPR, Tampa
Tracking as ClassificationH. Grabner, M. Grabner and H. Bischof. Real-time tracking
via On-line Boosting, BMVC 2006.
object
backgroundvs.
2008/12/09 - ICPR, Tampa 5Helmut Grabner - Computer Vision Laboratory – ETH Zurich
Tracking as ClassificationH. Grabner, M. Grabner and H. Bischof. Real-time tracking
via On-line Boosting, BMVC 2006.
object
backgroundvs.
2008/12/09 - ICPR, Tampa 6Helmut Grabner - Computer Vision Laboratory – ETH Zurich
search Region
actual object position
from time t to t+1 evaluate classifier on sub-patches
-
+
- -
-
create confidence map
analyze map and set newobject position
update classifier (tracker)
2008/12/09 - ICPR, Tampa 7Helmut Grabner - Computer Vision Laboratory – ETH Zurich
The Classifier
Combination of simple image featuresusing Boosting as Feature Selection
P. Viola and M. Jones. Rapid object detection using a boosted cascade of simple features. CVPR 2001.
2008/12/09 - ICPR, Tampa 8Helmut Grabner - Computer Vision Laboratory – ETH Zurich
Boosting
Strong classifier Weak classifier
Y. Freund and R. Schapire. A decision-theoretic generalization of on-line lear ning and an application to boosting. Journal of Computer and System Sciences, 1997.
Reweighting the training Examples
2008/12/09 - ICPR, Tampa 9Helmut Grabner - Computer Vision Laboratory – ETH Zurich
Boosting for Feature Selection
� Each feature corresponds to a weak classifier
K. Tieu and P. Viola. Booting Image Retrival, CVPR 2000Boosting is performed on the Selectors and not on
� On-line� Introducing “Selector”
� selects one feature from its local feature pool
2008/12/09 - ICPR, Tampa 10Helmut Grabner - Computer Vision Laboratory – ETH Zurich
H. Grabner and H., Bischof. On-line Boosting and Vision, CVPR 2006
the Selectors and not on the weak classifiers
directly.
H. Grabner and H., Bischof. On-line Boosting and Vision, CVPR 2006
2008/12/09 - ICPR, Tampa 11Helmut Grabner - Computer Vision Laboratory – ETH Zurich
Unsolved Problems…
2008/12/09 - ICPR, Tampa 12Helmut Grabner - Computer Vision Laboratory – ETH Zurich
Problems…
h1,1
one
traning
sample
h1,2
h2,1
h2,2
hN,1
hN,2
hN,mestimate
importance
estimate
importance
.
.
.
inital
importance .
.
.
.
hSelector1 hSelector2 hSelectorNN
h1,M h2,M
h2,m
hN,M
update update update
current strong classifier hStrong
repeat for each
trainingsample
.
. .
.
.
(i) TRAINING:Determine the Classifier
Complexity
2008/12/09 - ICPR, Tampa 13Helmut Grabner - Computer Vision Laboratory – ETH Zurich
h1,1
one
traning
sample
h1,2
h2,1
h2,2
hN,1
hN,2
hN,mestimate
importance
estimate
importance
.
.
.
inital
importance .
.
.
.
hSelector1 hSelector2 hSelectorNN
h1,M h2,M
h2,m
hN,M
update update update
current strong classifier hStrong
repeat for each
trainingsample
.
. .
.
.
(ii) TESTING:Optimization of the
classifier evaluation speed
2008/12/09 - ICPR, Tampa 14Helmut Grabner - Computer Vision Laboratory – ETH Zurich
Wald’sSequential
2008/12/09 - ICPR, Tampa 15Helmut Grabner - Computer Vision Laboratory – ETH Zurich
Sequential Probability Rate
Test (SPRT)
Abraham Wald (1902-1950)
Sequential Decision Making
� Sequential Decision Strategy S
Ordered sequence of measurements
decision
� Goal: Train (look for)
2008/12/09 - ICPR, Tampa 16Helmut Grabner - Computer Vision Laboratory – ETH Zurich
Average time-to-decision (-1/+1) Allowed false positive and false negative rate
Ordered sequence of measurements
Sequential Probability Ratio Test
2008/12/09 - ICPR, Tampa 17Helmut Grabner - Computer Vision Laboratory – ETH Zurich
(near) optimal setting
Likelihood ratio
� Likelihood ratio
� Replace with weak classifier
� 1D projection
WaldBoost (1)J. Sochman, J. Matas, WaldBoost – Learning for Time
Constrained Sequential Detection, CVPR, 2005.
� 1D projection
2008/12/09 - ICPR, Tampa 18Helmut Grabner - Computer Vision Laboratory – ETH Zurich
Boosting
� Threshed on the boosted classifier response
WaldBoost (2)J. Sochman, J. Matas, WaldBoost – Learning for Time
Constrained Sequential Detection, CVPR, 2005.
� Used in…� … training for bootstrapping important samples� … testing for early stopping (fast decision making)
2008/12/09 - ICPR, Tampa 19Helmut Grabner - Computer Vision Laboratory – ETH Zurich
h1,1
one
traning
sample
h1,2
h1,M
h2,1
h2,2
h2,M
h2,m
hN,1
hN,2
hN,M
hN,m
estimate
importance
estimate
importance
.
.
.
inital
importance .
.
.
.
.
.
.
.
.
hSelector1 hSelector2 hSelectorN
On-line Boosting WaldBoost
2008/12/09 - ICPR, Tampa 20Helmut Grabner - Computer Vision Laboratory – ETH Zurich
update update update
current strong classifier hStrong
repeat for each
trainingsample
On-line Wald Boost
On-line WaldBoost
2008/12/09 - ICPR, Tampa 21Helmut Grabner - Computer Vision Laboratory – ETH Zurich
Back to Visual Tracking...
(i) TRAINING:Determine the Classifier
Complexity
object
backgroundvs.
2008/12/09 - ICPR, Tampa 22Helmut Grabner - Computer Vision Laboratory – ETH Zurich
search Region
actual object position
from time t to t+1 evaluate classifier on sub-patches
(ii) TESTING:Optimization of the
classifier evaluation speed
-
+
- -
-
create confidence map
analyze map and set newobject position
update classifier (tracker)
2008/12/09 - ICPR, Tampa 23Helmut Grabner - Computer Vision Laboratory – ETH Zurich
Experiments - Tracking
Tracking Result Confidence Map
2008/12/09 - ICPR, Tampa 24Helmut Grabner - Computer Vision Laboratory – ETH Zurich
Experiment: Speedup
On average a factor of
5-10!
2008/12/09 - ICPR, Tampa 25Helmut Grabner - Computer Vision Laboratory – ETH Zurich
5-10!
Conclusion and Outlook
� Wald-decision theory combined with on-line boosting for feature selection
� (i) optimized classifier evaluation
On-line Boosting
� (i) optimized classifier evaluation speed
� (ii) automatic determination of the classifier complexity
2008/12/09 - ICPR, Tampa 26Helmut Grabner - Computer Vision Laboratory – ETH Zurich
On-line WALD-Boosting
Conclusion and Outlook
On-line WALD-Boosting
DetectionBackground ModelingTracking Background ModelingTracking
This presentation
2008/12/09 - ICPR, Tampa 27Helmut Grabner - Computer Vision Laboratory – ETH Zurich
Thank you for your attention!
2008/12/09 - ICPR, Tampa 28Helmut Grabner - Computer Vision Laboratory – ETH Zurich
Thank you for your attention!
Recommended