Full-scaled deep metric learning for pedestrian re-identification

The pedestrian re-identification problem (i.e., re-id) is essential and pre-requisite in multi-camera video surveillance studies, provided the fact that pedestrian targets need to be accurately re-identified across a network of multiple cameras with non-overlapping fields of views before other post-hoc high-level utilizations (i.e., tracking, behaviors analyses, activities monitoring, etc.) can be carried out. Driven by recent developments in deep learning techniques, the important re-id problem is often tackled via either deep discriminant learning or deep generative learning techniques. However, most contemporary deep learning-based models with tremendously deep structures are not easy to be trained because of the notorious vanishings gradient problem. In this study, a novel full-scaled deep discriminant learning model is proposed. The novelty of the full-scale model is significant, as three crucial concepts in designing a deep learning model, including depth, width, and cardinality, are all taken into consideration, simultaneously. Therefore, the new model needs not to be tremendously deep but is more convenient to be trained. Moreover, based on the new model, a novel deep metric learning method is proposed to further solve the important re-id problem. Technically, two algorithms either based on the conventional SGD (stochastic gradient descent) or an alternative more efficient PGD (proximal gradient descent) are both derived. For experimental analyses, the newly introduced full-scaled deep metric learning method has been comprehensively compared with dozens of popular re-id methods proposed from either deep learning or shallow learning perspectives. Several well-known public re-id datasets have been incorporated and rigorous statistical analyses have been carried out to compare all methods regarding their re-id performance. The superiority of the novel full-scaled deep metric learning method has been substantiated, from the statistical point of view.