Xiu-Shen Wei 1[0000−0002−8200−1845] , Chen-Lin Zhang 2[0000−0002−3168−1852] , Lingqiao Liu 3[0000−0003−3584−795X] , Chunhua Shen 3[0000−0002−8648−8718] , and Jianxin Wu 2[0000−0002−2085−7568]Abstract Vehicle re-identification is an important problem and becomes desirable with the rapid expansion of applications in video surveillance and intelligent transportation. By recalling the identification process of human vision, we are aware that there exists a native hierarchical dependency when humans identify different vehicles. Specifically, humans always firstly determine one vehicle's coarse-grained category, i.e., the car model/type. Then, under the branch of the predicted car model/type, they are going to identify specific vehicles by relying on subtle visual cues, e.g., customized paintings and windshield stickers, at the fine-grained level. Inspired by the coarse-to-fine hierarchical process, we propose an end-to-end RNN-based Hierarchical Attention (RNN-HA) classification model for vehicle re-identification. RNN-HA consists of three mutually coupled modules: the first module generates image representations for vehicle images, the second hierarchical module models the aforementioned hierarchical dependent relationship, and the last attention module focuses on capturing the subtle visual information distinguishing specific vehicles from each other. By conducting comprehensive experiments on two vehicle re-identification benchmark datasets VeRi and VehicleID, we demonstrate that the proposed model achieves superior performance over state-of-theart methods.
Coarse-to-fineModel level Vehicle level Query … … … … Figure 1: Illustration of coarse-to-fine hierarchical information as a latent but crucial cue for vehicle re-identification. (Best viewed in color and zoomed in.) has diverse applications in video surveillance [30], intelligent transportation [37]and urban computing [40]. Moreover, vehicle re-identification has recently drawn increasing attentions in the computer vision community [19,20,23]. Compared with the classic person re-identification problem, vehicle re-identification could be more challenging as different specific vehicles can only be distinguished by slight and subtle differences, such as some customized paintings, windshield stickers, favorite decorations, etc. Nevertheless, there still conceals some latent but crucial information for handling this problem. As shown in Fig. 1, when humans identify different vehicles, they always follow a coarse-to-fine identification process. Specifically, we tend to firstly determine this specific vehicle belongs to which car model/type. The first step can eliminate many distractors, i.e., vehicles with similar subtle visual appearances but belonging to the other different car models/types. In the following, within the candidate vehicle set of the same car model/type, humans will carefully distinguish different vehicles from each other by using these subtle visual cues. Apparently, there is a hierarchical dependency in this coarse-to-fine process, which is yet neg...