Survey on Unsupervised Person Re-Identification

Abstract

The primary task of person Re-IDentification (ReID) is to identify and track a specific pedestrian across multiple non-overlapping cameras. With the development of deep neural networks and owing to the increasing demand for intelligent video surveillance, ReID has gradually attracted research attention. Most existing ReID methods primarily adopt labeled data for supervised training; however, the high annotation cost makes the scaling supervised ReID to large unlabeled datasets challenging. The paradigm of unsupervised ReID can significantly alleviate such issues. This can improve its applicability to real-life scenarios, enhancing its research potential. Although several ReID surveys have been published, they have primarily focused on supervised methods and their applications. This survey systematically reviews, analyzes, and summarizes existing ReID studies to provide a reference for researchers in this field. First, the ReID methods are comprehensively reviewed in an unsupervised setting. Based on the availability of source domain labels, the unsupervised ReID methods are categorized into unsupervised domain adaptation methods and fully unsupervised methods. Additionally, their merits and drawbacks are discussed. Subsequently, the benchmark datasets widely evaluated in ReID research are summarized, and the performance of different ReID methods on these datasets is compared. Finally, the current challenges in this field are discussed and potential future directions are proposed.