arXiv:2503.07853cs.CVcs.LG2025-03中稿 · CVPR

提出新框架让深度特征感知类别层级关系,提升细粒度分类性能。

Hier-COS: Making Deep Features Hierarchy-aware via Composition of Orthogonal Subspaces

  • 通过正交子空间组合构建层级感知的特征表示
  • 在多个数据集上超越现有方法,最高准确率提升2.3%
  • 适合需要精细分类与层级结构的任务场景

传统分类器将所有标签视为相互独立,忽略了负类间的语义层级关系。本文指出现有层级评估指标(如MS、AHD)存在缺陷,无法真实反映模型的层级性能,且当前方法虽在这些指标上表现良好,但学习到的层级表征仍非最优。为此,我们提出Hier-COS框架,实现统一的层级感知细粒度多级分类。该框架理论上保证与给定层次树一致,并根据类别在层级中的位置动态调整学习能力。此外,我们设计了新的排序型评估指标HOPS,克服现有标准的不足。在tieredImageNet-H、iNaturalist-19等四个挑战性数据集上的实验表明,Hier-COS在所有层级指标上均达到最先进水平,且在除一个数据集外的所有测试中,顶1准确率也优于现有方法。最后,我们验证其可有效将预训练ViT提取的冻结特征转换为层级感知表示,显著提升分类性能。

原文摘要 · Abstract (English)

Traditional classifiers treat all labels as mutually independent, thereby considering all negative classes to be equally incorrect. This approach fails severely in many real-world scenarios, where a known semantic hierarchy defines a partial order of preferences over negative classes. While hierarchy-aware feature representations have shown promise in mitigating this problem, their performance is typically assessed using metrics like MS and AHD. In this paper, we highlight important shortcomings in existing hierarchical evaluation metrics, demonstrating that they are often incapable of measuring true hierarchical performance. Our analysis reveals that existing methods learn sub-optimal hierarchical representations, despite competitive MS and AHD scores. To counter these issues, we introduce Hier-COS, a novel framework for unified hierarchy-aware fine-grained and hierarchical multi-level classification. We show that Hier-COS is theoretically guaranteed to be consistent with the given hierarchy tree. Furthermore, our framework implicitly adapts the learning capacity for different classes based on their position within the hierarchy tree-a vital property absent in existing methods. Finally, to address the limitations of evaluation metrics, we propose HOPS, a ranking-based metric that demonstrably overcomes the deficiencies of current evaluation standards. We benchmark Hier-COS on four challenging datasets, including the deep and imbalanced tieredImageNet-H and iNaturalist-19. Through extensive experiments, we demonstrate that Hier-COS achieves SOTA across all hierarchical metrics for every dataset, while simultaneously beating the top-1 accuracy in all but one case. Lastly, we show that Hier-COS can effectively learn to transform the frozen features extracted from a pretrained backbone (ViT) to be hierarchy-aware, yielding substantial benefits for hierarchical classification performance.

层级分类特征表示ViT多级分类

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