text: Group re-identification (G-ReID) is an important yet less-studied task. Its challenges not only lie in appearance changes of individuals which have been well-investigated in general person re-identification (ReID), but also derive from group layout and membership changes. So the key task of G-ReID is to learn representations robust to such changes. To address this issue, we propose a Transferred Single and Couple Representation Learning Network (TSCN). Its merits are two aspects: 1) Due to the lack of labelled training samples, existing G-ReID methods mainly rely on unsatisfactory hand-crafted features. To gain the superiority of deep learning models, we treat a group as multiple persons and transfer the domain of a labeled ReID dataset to a G-ReID target dataset style to learn single representations. 2) Taking into account the neighborhood relationship in a group, we further propose learning a novel couple representation between two group members, that achieves more discriminative power in G-ReID tasks. In addition, an unsupervised weight learning method is exploited to adaptively fuse the results of different views together according to result patterns. Extensive experimental results demonstrate the effectiveness of our approach that significantly outperforms state-of-the-art methods by 11.7 CMC-1 on the Road Group dataset and by 39.0 CMC-1 on the DukeMCMT dataset.
  @cite_7: In a crowded public space, people often walk in groups, either with people they know or strangers. Associating a group of people over space and time can assist understanding individual’s behaviours as it provides vital visual context for matching individuals within the group. Seemingly an ‘easier’ task compared with person matching given more and richer visual content, this problem is in fact very challenging because a group of people can be highly non-rigid with changing relative position of people within the group and severe self-occlusions. In this paper, for the first time, the problem of matching associating groups of people over large space and time captured in multiple non-overlapping camera views is addressed. Specifically, a novel people group representation and a group matching algorithm are proposed. The former addresses changes in the relative positions of people in a group and the latter deals with variations in illumination and viewpoint across camera views. In addition, we demonstrate a notable enhancement on individual person matching by utilising the group description as visual context. Our methods are validated using the 2008 i-LIDS Multiple-Camera Tracking Scenario (MCTS) dataset on multiple camera views from a busy airport arrival hall.
  @cite_23: This paper addresses an important yet less-studied problem: re-identifying groups of people in different camera views. Group re-identification (Re-ID) is very challenging since it is not only interfered by view-point and human pose variations in the traditional single-object Re-ID tasks, but also suffers from group layout and group member variations. To handle these issues, we propose to leverage the information of multi-grain objects: individual person and subgroups of two and three people inside a group image. We compute multi-grain representations to characterize the appearance and spatial features of multi-grain objects and evaluate the importance weight of each object for group Re-ID, so as to handle the interferences from group dynamics. We compute the optimal group-wise matching by using a multi-order matching process based on the multi-grain representation and importance weights. Furthermore, we dynamically update the importance weights according to the current matching results and then compute a new optimal group-wise matching. The two steps are iteratively conducted, yielding the final matching results.Experimental results on various datasets demonstrate the effectiveness of our approach.
  @cite_25: In this paper, we present a new solution to the problem of matching groups of people across multiple non-overlapping cameras. Similar to the problem of matching individuals across cameras, matching groups of people also faces challenges such as variations of illumination conditions, poses and camera parameters. Moreover, people often swap their positions while walking in a group. In this paper, we propose to use covariance descriptor in appearance matching of group images. Covariance descriptor is shown to be a discriminative descriptor which captures both appearance and statistical properties of image regions. Furthermore, it presents a natural way of combining multiple heterogeneous features together with a relatively low dimensionality. Experimental results on two different datasets demonstrate the effectiveness of the proposed method.
  @cite_20: Associating groups of people across non-overlapping camera views is an important but unsolved problem. Compared with the similar person re-identification task, group re-identification introduces some new challenges, such as significant deformation in uncontrolled directions, great intra-group occlusions and so on. In this paper, we propose a novel patch matching based framework for group re-identification. Discriminative salience channels are learned to filter out highly unreliable and non-informative patch matches between two group images, while retain true matches undergoing appearance variations. The resulting candidate correspondences are further explored by the proposed consistent matching process, which prefers coherent matches in true group image pairs. The effectiveness of our approach is validated on two group re-identification datasets: ZeCSS and i-LIDS MCTS. It outperforms state-of-the-art methods on both datasets.
  @cite_11: Person re-identification is best known as the problem of associating a single person that is observed from one or more disjoint cameras. The existing literature has mainly addressed such an issue, neglecting the fact that people usually move in groups, like in crowded scenarios. We believe that the additional information carried by neighboring individuals provides a relevant visual context that can be exploited to obtain a more robust match of single persons within the group. Despite this, re-identifying groups of people compound the common single person re-identification problems by introducing changes in the relative position of persons within the group and severe self-occlusions. In this paper, we propose a solution for group re-identification that grounds on transferring knowledge from single person reidentification to group re-identification by exploiting sparse dictionary learning. First, a dictionary of sparse atoms is learned using patches extracted from single person images. Then, the learned dictionary is exploited to obtain a sparsity-driven residual group representation, which is finally matched to perform the re-identification. Extensive experiments on the i-LIDS groups and two newly collected datasets show that the proposed solution outperforms stateof-the-art approaches.
summary: . Recently, relatively fewer works have focused on G-ReID tasks @cite_25 @cite_11 @cite_7 @cite_20 @cite_23 , compared to general ReID tasks. Some of them mainly attempted to extract global or semi-global features. For example, Cai al @cite_25 proposed a discriminative covariance descriptor to obtain both global and statistical features. Zheng al @cite_7 proposed semi-global features by segmenting a group image into several ring regions. Since persons in a group often change their locations under different views ( , layout-change), global and semi-global features are usually sensitive to such changes. In order to make use of individuals' features in the groups, Zhu al @cite_20 introduced patch matching between two group photos. However, it requires prior restrictions on vertical misalignments, making it unworkable under certain circumstances. Xiao al @cite_23 leveraged multi-grain information and attempted to fully capture the characteristics of a group. This approach, however, involves too much redundant information and employs common hand-crafted features, thereby making its accuracy not satisfactory enough.