Coarse Labels Matter: Revisiting the Role of Coarse-Grained Supervision in Fine-Grained Learning

The prohibitive cost of acquiring high-quality fine-grained annotations has spurred significant interest in leveraging readily available coarse labels for fine-grained learning. However, prevailing approaches tend to rely on increasingly sophisticated unsupervised methods to define fine-grained proxy tasks, with coarse labels often playing an auxiliary role. In this paper, we propose CSer, a framework designed to maximize the utility of coarse label information for Coarse-to-Fine learning. Specifically, to reconcile the conflict between preserving fine-grained feature diversity and maintaining strong coarse-grained supervision, our coarse-grained self-distillation strategy fortifies the backbone's discriminative power by distilling knowledge from the final classifier to intermediate layers. Concurrently, we introduce dense supervision on common component features within each coarse class, which are decoupled using Non-negative Matrix Factorization. This enhances responses to distinct components, thereby mitigating the simplicity bias in embeddings that can arise under coarse supervision. Moreover, we leverage relationships among intra-class samples to dynamically adjust the negative sampling strategy in contrastive learning, thereby constructing distinct fine-grained class relationships tailored to different coarse classes. Extensive experiments conducted on multiple benchmark datasets demonstrate the effectiveness of our method, yielding state-of-the-art results surpassing competing methods.