Multi-Context Grouped Attention for Unsupervised Person Re-Identification

Recent advancements like multiple contextual analysis, attention mechanisms, distance-aware optimization, and multi-task guidance have been widely used for supervised person re-identification (ReID), but the implementation and effects of such methods in unsupervised ReID frameworks are non-trivial and unclear, respectively. Moreover, with increasing size and complexity of image- and video-based ReID datasets, manual or semi-automated annotation procedures for supervised ReID are becoming labor intensive and cost prohibitive, which is undesirable especially considering the likelihood of annotation errors increase with scale/complexity of data collections. Therefore, we propose a new iterative clustering framework that is insensitive to annotation errors and over-fitting ReID annotations (i.e., labels). Our proposed unsupervised framework incorporates (a) a novel multi-context group attention architecture that learns a holistic attention map from multiple local and global contexts, (b) an unsupervised clustering loss function that down-weights easily discriminative identities, and (c) a background diversity term that helps cluster persons across different cross-camera views without leveraging any identification or camera labels. We perform extensive analysis using the DukeMTMC-VideoReID and MARS video-based ReID datasets and the MSMT17 image-based ReID dataset. Our approach is shown to provide a new state-of-the-art performance for unsupervised ReID, reducing the rank-1 performance gap between supervised and unsupervised ReID to 1.1%, 12.1%, and 21.9% from 6.1%, 17.9%, and 22.6% for DukeMTMC, MARS, and MSMT17 datasets, respectively.