Recognition of high-level group activities based on activities of individual members

The paper describes a methodology for the recognition of high-level group activities. Our system recognizes group activities including group actions, group-persons interactions, group-group (i.e. inter-group) interactions, intra-group interactions, and their combinations described using a common representation scheme. Our approach is to represent various types of complex group activities with a programming language-like representation, and then to recognize represented activities based on the recognition of activities of individual group members. A hierarchical recognition algorithm is designed for the recognition of high-level group activities. The system was tested to recognize activities such as 'two groups fighting, 'a group of thieves stealing an object from another group, and 'a group of policemen arresting a group of criminals (or a criminal)'. Videos downloaded from YouTube as well as videos that we have taken are tested. Experimental results shows that our system recognizes complicated group activities, and it does it more reliably and accurately compared to previous approaches.