Alignment Before Aggregation: Trajectory Memory Retrieval Network for Video Object Segmentation

Memory-based methods in semi-supervised video object segmentation task achieve competitive performance by performing dense matching between query and memory frames. However, most of the existing methods neglect the fact that videos carry rich temporal information yet redundant spatial information. In this case, direct pixel-level global matching will lead to ambiguous correspondences. In this work, we reconcile the inherent tension of spatial and temporal information to retrieve memory frame information along the object trajectory, and propose a novel and coherent Trajectory Memory Retrieval Network (TMRN) to equip with the trajectory information, including a spatial alignment module and a temporal aggregation module. The proposed TMRN enjoys several merits. First, TMRN is empowered to characterize the temporal correspondence which is in line with the nature of video in a data-driven manner. Second, we elegantly customize the spatial alignment module by coupling SVD initialization with agent-level correlation for representative agent construction and rectifying false matches caused by direct pairwise pixel-level correlation, respectively. Extensive experimental results on challenging benchmarks including DAVIS 2017 validation / test and Youtube-VOS 2018 / 2019 demonstrate that our TMRN, as a general plugin module, achieves consistent improvements over several leading methods.