  Class imbalance is a common challenge in real-world recognition tasks, where
the majority of classes have few samples, also known as tail classes. We
address this challenge with the perspective of generalization and empirically
find that the promising Sharpness-Aware Minimization (SAM) fails to address
generalization issues under the class-imbalanced setting. Through investigating
this specific type of task, we identify that its generalization bottleneck
primarily lies in the severe overfitting for tail classes with limited training
data. To overcome this bottleneck, we leverage class priors to restrict the
generalization scope of the class-agnostic SAM and propose a class-aware
smoothness optimization algorithm named Imbalanced-SAM (ImbSAM). With the
guidance of class priors, our ImbSAM specifically improves generalization
targeting tail classes. We also verify the efficacy of ImbSAM on two
prototypical applications of class-imbalanced recognition: long-tailed
classification and semi-supervised anomaly detection, where our ImbSAM
demonstrates remarkable performance improvements for tail classes and anomaly.
Our code implementation is available at
https://github.com/cool-xuan/Imbalanced_SAM.
