In recent years, SiamFC-based trackers have received much attention because of their great potentials in balancing tracking accuracy and speed. However, the robustness of most such trackers is greatly affected by the large deformations of the target. We argue that in the cross-correlation operation which is widely used by modern SiamFC-based trackers, the static correlation between the template
... [Show full abstract] kernel and the features map of test sample is difficult to adapt to the large deformations of the target. In this paper, we propose the Siamese deformable cross-correlation network (SiamDCN), which introduces the deformable cross-correlation operation into SiamFC in an online self-adaptive way, for robust visual tracking. Compared to the previous SiamFC-based trackers, the proposed SiamDCN is more robust to the large deformations of the target through dynamically and adaptively adjusting the locations of correlation calculations for each element of the template kernel in the cross-correlation operation. Moreover, we build a twofold Siamese network, named SiamDCN+, which consists of a SiamDCN branch and a SiamFC branch, for accurate and real-time visual tracking after observing that the features learned in SiamFC are static and discriminative, whereas the features learned in SiamDCN are dynamic and robust, and they complement each other. Extensive experiments on three public benchmarks, OTB2015, VOT2016, and VOT2017, show that the proposed SiamDCN achieves superior localization performance than its baseline tracker SiamFC and the proposed SiamDCN+ achieves competitive performance compared to the state-of-the-art real-time trackers, while running over 40 FPS.