QuadTreeCapsule: QuadTree Capsules for Deep Regression Tracking

Benefit from the capability of capturing part-to-whole relationships, Capsule Network has been successful in many vision tasks. However, their high computational complexity poses a significant obstacle to applying them to visual tracking, requiring fast inference. In this paper, we introduce the idea of QuadTree Capsules, which explores the property of part-to-whole relationships endowed by the Capsule Network by significantly reducing the computational complexity. We build capsule pyramids and select meaningful relationships in a coarse-to-fine manner, dubbed as QuadTreeCapsule. Specifically, the top K capsules with the highest activation values are selected, and routing is only calculated within the relevant regions corresponding to these top K capsules with a novel symmetric guided routing algorithm. Additionally, considering the importance of temporal relationships, a multi-spectral pose matrix attention mechanism is developed for more accurate spatio-temporal capsule assignments between two sets of capsules. Moreover, during online inference, we shift part of the spatio-temporal capsules long the temporal dimension, facilitating information exchanged among neighboring frames. Extensive experimentation has proved the effectiveness of our methodology, which achieves state-of-the-art results compared with other tracking methods on eight widely-used benchmarks. Our tracker runs at approximately 43 fps on GPU.