We present an approach to visual tracking based on dividing a
target into multiple regions, or fragments. The target is represented
by a Gaussian mixture model in a joint feature-spatial
space, with each ellipsoid corresponding to a different fragment.
The fragments are automatically adapted to the image
data, being selected by an efficient region-growing procedure
and updated according to a weighted average of the past and
present image statistics. Modeling of target and background
are performed in a Chan-Vese manner, using the framework
of level sets to preserve accurate boundaries of the target.
The extracted target boundaries are used to learn the dynamic
shape of the target over time, enabling tracking to continue
under partial and total occlusion. Experimental results on a
number of challenging sequences demonstrate the effectiveness
of the technique.