Distributionally Robust Loss for Long-Tailed Multi-Label Image Classification

The binary cross-entropy (BCE) loss function is widely utilized in multi-label classification (MLC) tasks, treating each label independently. The log-sum-exp pairwise (LSEP) loss, which emphasizes higher logits for positive classes over negative ones within a sample and accounts for label dependencies, has demonstrated effectiveness for MLC. However, our experiments suggest that its performance in long-tailed multi-label classification (LTMLC) appears to be inferior to that of BCE. In this study, we investigate the impact of the log-sum-exp operation on recognition and explore optimization avenues. Our observations reveal two primary shortcomings of LSEP that lead to its poor performance in LTMLC: 1) the indiscriminate use of label dependencies without consideration of the distribution shift between training and test sets, and 2) the overconfidence in negative labels with features similar to those of positive labels. To mitigate these problems, we propose a distributionally robust loss (DR), which includes class-wise LSEP and a negative gradient constraint. Additionally, our findings indicate that the BCE-based loss is somewhat complementary to the LSEP-based loss, offering enhanced performance upon integration. Extensive experiments conducted on two LTMLC datasets, VOC-LT and COCO-LT, demonstrate the consistent effectiveness of our proposed method. The code will be made publicly available shortly.