same cluster labels. The four cases are:
(i) Unchanged cluster. We check whether the graphs of the
connected components induced by At are formed by the
feature vectors from old clusters. This operation is performed
by checking the ages of all the feature vectors within the
graphs and their corresponding cluster indexes assigned to the
previous frame. Then we maintain the same old cluster label
for the feature vectors (i.e. no new clusters are formed).
(ii) Enlarged cluster. We check whether some graphs of the
connected components of At are formed by the feature vectors
from an old cluster, and the rest of the graphs are formed by
the feature vectors in Ft. We propagate the same older cluster
label to the newly included feature vectors.
(iii) New cluster. We check whether all the graphs of the
connected components of At are formed by the feature vectors
in Ft only, and then assign a new cluster label to the feature
vectors.
(iv) Merged cluster. We check whether the connected components
of At are formed by feature vectors from different old
clusters, and then we assign to all the feature vectors the label
of the old cluster with the largest number of feature vectors
before the merging.
This four-case cluster assignment is summarized in Algorithm