Involved people: Duc Phu CHAU, Francois BREMOND and Monique THONNAT
SUP (Scene Unsderstanding Platform, developped by Stars team) provides an object apperance-based tracking algorithm. This tracker includes two main plugins: ParametrableF2Ftracking and LTT.
The objective of ParametrableF2Ftracking plugin is to establish object links with a sliding time window. For each detected object pair in a given temporal window of size T1, we compute the link score (i.e. instantaneous similarity). A temporary link is established between two objects when their link score is greater or equal to a predefined threshold. At the end of this stage, we obtain a weighted graph whose vertices are the detected objects in the considered temporal window and whose edges are the temporarily established links. Each edge is associated with a score representing the link score between its two vertices (see the below figure). For each detected object, we search its matched objects in a predefined radius and in a given temporal window to establish possible links so that even when one mobile object cannot be detected in some frames, it still can find its successor objects.
The graph representing the established links of the detected objects in a temporal window of size T1 frames.
The goal of the LTT plugin is to determine the trajectories of the mobile objects. For each object ot detected at instant t (called son object), we consider all its matched objects (i.e. objects with temporarily established links) in previous frames (called father objects) that do not have yet official links (i.e. trajectories) to any objects detected at the following frames. For such an object pair, we define a global score in function of link score (i.e. instantenous score) and long-term score.
The father object having the highest global similarity is considered as a temporary father of object ot. After considering all objects at instant t, if more than one object get a same object as a temporary father, the pair father-son corresponding to the highest global score value is kept, and the link between this pair is official (i.e. become officially a trajectory segment). A mobile object is no longer tracked if it cannot establish any official links in T1 consecutive frames.
A reference of this work can be found here.