Formulation, detection and application of occlusion states (Oc-7) in the context of multiple object tracking

Occlusion is often thought of as a challenge for visual algorithms, specially tracking. Existing literature, however, has identified a number of occlusion categories in the context of tracking in ad hoc manner. We propose a systematic approach to formulate a set of occlusion cases by considering the spatial relations among object support(s) (projections on the image plane) with the detected foreground blob(s), to show that only 7 occlusion states are possible. We designate the resulting qualitative formalism as Oc-7, and show how these occlusion states can be detected and used effectively for the task of multi-object tracking under occlusion of various types. The object support is decomposed into overlapping patches which are tracked independently on the occurrence of occlusions. As a demonstration of the application of these occlusion states, we propose a reasoning scheme for selective tracker execution and object feature updates to track multiple objects in complex environments.