Sparse Relation Graph for Group Activity Recognition

Modeling relations between actors is critical for understanding group activities of dynamic scenes. Existing Group Activity Recognition (GAR) methods usually build strong connection in each actor pair. However, not all the connetions are necessary because not all actors are visible or related to each other. Based on this observation, we provide a Sparse Relation Graph (SRG) for GAR, in which the key relations are focused to mine more discriminative features. Then a graph convolutional network is designed for automatically learning the key relations. Extensive experiments on two popular group activity datasets, the Volleyball dataset and the Collective Activity dataset, demonstrate the effectiveness of our method. Especially in the Volleyball dataset, SRG can get better performance with less but delicate information.