Discriminative context models for collective activity recognition

Context information has been widely studied for recognizing collective activities. Most existing works assume that all individuals in a single image share the same activity label. However, in many cases, multiple activities can be coexisted and serve as the context for each other in real-world scenarios. Based on this observation, we propose a novel approach to model both the intra-class and inter-class behavior interactions among persons in the scenario. By introducing the intra-class and inter-class context descriptors, we propose a unified discriminative model to jointly capture the individual appearance information and the context patterns around the focal person in a max-margin framework. Finally, a greedy forward search method is utilized to optimally label the activities in the testing scene. Experimental results demonstrate the superiority of our approach in activity recognition.