STCA: Utilizing a spatio-temporal cross-attention network for enhancing video person re-identification

Video-based re-identification (ReID) is a crucial task in computer vision that draws increasing attention due to advances in deep learning (DL) and modern computational devices. Despite recent success with CNN architectures, single models (e.g., 2D-CNNs or 3D-CNNs) alone failed to leverage temporal information with spatial cues. This is due to uncontrolled surveillance scenarios and variable poses leading to inevitable misalignment of ROIs across the tracklets, which is accompanied by occlusion and motion blur. In this context, designing temporal and spatial cues for two different models and their combinations can be beneficial, considering the global of a video-tracklet. 3D-CNNs allow encoding of temporal information while 2D-CNNs extract spatial or appearance information. In this paper, we propose a Spatio-Temporal Cross Attention (STCA) network to utilize both 2D-CNNs and 3D-CNNs that calculate the cross attention mapping both from the layer of 3D-CNNs and 2D-CNNs along a person's trajectory to gate the following layers of 2D-CNNs; and highlight relevant appearance features for the person ReID. Given an input tracklet, the proposed cross attention (CA) is able to capture the salient regions that propagate throughout the tracklet to obtain the global view. This provides a spatio-temporal attention approach that can be dynamically aggregated with spatial features of 2D-CNNs to perform finer-grained recognition. Additionally, we exploit the advantage of utilizing cosine similarity while triplet sampling as well as for calculating the final recognition score. Experimental analyses on three challenging benchmark datasets indicate that integrating spatio-temporal cross attention into the state-of-the-art video ReID backbone CNN architecture allows for improving their recognition accuracy.