Hashing person re-ID with self-distilling smooth relaxation

Person re-identification (re-ID) has made substantial progress in recent years; however, it is still challenging to search for the target person in a short time. Re-ID with deep hashing is a shortcut for that but, limited by the expression of binary code, the performance of the hashing method is not satisfactory. Besides, to further speed up retrieval, researchers tend to reduce the number of feature bits, which will cause more performance degradation. In this paper, we design the attribute-based fast retrieval (AFR), which leverages the attribute prediction of the model trained in a binary classification manner tailor-made for hashing. The attribute information is also used to refine the global feature representation by an attribute-guided attention block (AAB). Then, to fully exploit deep feature to generate the hash codes, we propose a binary code learning method, named self-distilling smooth relaxation (SSR). In this method, a simple yet effective regularization is presented to distill the quantized knowledge in the model itself, thus mitigating the lack of semantic guidance in the traditional non-linear relaxations. We manually label attributes for each person in dataset CUHK03 and evaluate our method on four authoritative public benchmarks (Market-1501, Market-1501+500K, CUHK03, and DukeMTMC-reID). The experimental results indicate that with the SSR and AAB, we surpass all the state-of-the-art hashing methods. And compared with reducing the feature bits, the AFR strategy is more effective to save search time.