Tracking people across disjoint camera views
- Publication Type:
- Thesis
- Issue Date:
- 2009
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Tracking people around surveillance systems is becoming increasingly
important in the current security conscious environment. This thesis presents
a framework to automatically track the movements of individual people in
large video camera networks, even where there are gaps between camera
views. It is designed to assist security operators, or police investigations by
providing additional information about the location of individuals throughout
the surveillance area. Footage from an existing surveillance system has
been used to test the framework under real conditions. The framework uses
the similarity of robust shape and appearance features to match tracks. These
features are extracted to build an object feature model as people move within
a single camera view, which can be compared across cameras. The integration
of matching similarities in the temporal domain increases the robustness
to errors of many kinds. Frames with significant segmentation errors can be
automatically detected and removed based upon their lack of similarity to
the other models within the same track, increasing robustness.
The shape and appearance features used to generate the object models
are based upon features humans habitually use for identifying individuals.
They include a height estimate, a Major Colour Representation (MCR) of
the individuals global colours, and estimates of the colours of the upper
and lower portions of clothing. The fusion of these features is shown to
be complementary, providing increased discrimination between individuals.
The MCR colour features are improved through the mitigation of illumination
changes using controlled equalisation, which improves the accuracy
in matching colour under normal surveillance conditions and requires no
training or scene knowledge. The incorporation of other features into this
framework is also relatively straightforward.
This track matching framework was tested upon four individuals across
two video cameras of an existing surveillance system. Existing infrastructure
and actors were used to ensure that ground truth is available. Specific
cases were constructed to test the limitations of the system when similar
clothing is worn. In the data, the height difference ranges from 5 to 30
centimetres, and individuals may only be wearing 50% of similar clothing
colours. The accuracy of matching an individual was as high as 91% with
only 5% false alarms when all the system components were used. This may
not become a fully automated system, but could be used in semi-automated
or human assisted systems, or as the basis for further research into improved
automated surveillance. Application areas range from forensic surveillance
to the matching of the movements of key individuals throughout a surveillance
network and possibly even target location.
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