Lord of the Rings: Hanoi Pooling and Self-Knowledge Distillation for Fast and Accurate Vehicle Reidentification

Vehicle reidentification has seen increasing interest, thanks to its fundamental impact on intelligent surveillance systems and smart transportation. The visual data acquired from monitoring camera networks come with severe challenges, including occlusions, color and illumination changes, as well as orientation issues (a vehicle can be seen from the side/front/rear due to different camera viewpoints). To deal with such challenges, the community has spent much effort in learning robust feature representations that hinge on additional visual attributes and part-driven methods, but with the side effects of requiring extensive human annotation labor as well as increasing computational complexity. In this article, we propose an approach that learns a feature representation robust to vehicle orientation issues without the need for extra-labeled data and adding negligible computational overheads. The former objective is achieved through the introduction of a Hanoi pooling layer exploiting ring regions and the image pyramid approach yielding a multiscale representation of vehicle appearance. The latter is tackled by transferring the accuracy of a deep network to its first layers, thus reducing the inference effort by the early stop of a test example. This is obtained by means of a self-knowledge distillation framework encouraging multiexit network decisions to agree with each other. Results demonstrate that the proposed approach significantly improves the accuracy of early (i.e., very fast) exits while maintaining the same accuracy of a deep (slow) baseline. Moreover, our solution obtains the best existing performance on three benchmark datasets. ¹¹

[Online]. Available: https://github.com/iN1k1/.

I. Introduction

The extensive deployment of traffic monitoring cameras has generated a great amount of visual data for various applications such as intelligent surveillance systems [1], smart transportation [2], and urban informatics [3]. A paramount problem in such analytics is the association of targets among disjoint cameras. When targets to reassociate are vehicles, the problem is known as vehicle reidentification (VeRe-ID). As shown in [4], the problem is extremely challenging since vehicles present a high intraclass variability (caused by the diversity of car shapes from different viewpoints) tied with a small interclass variability (models produced by various manufacturers are limited in their shapes and colors).