arXiv:2607.09832cs.LGcs.CV2026-07

仅重训分类器就能显著提升长尾识别性能,简单有效。

A Strong Balanced-Softmax Classifier-Retraining Baseline for Long-Tailed Recognition

  • 先用平衡Softmax训练主干和分类器,再只更新分类器
  • 在多个数据集上少样本准确率提升5.15至9.78点
  • 适合想快速改进分类器的工程师或研究者

长尾识别方法通常通过修改损失、边界或表示来缓解常见类别的主导问题。本文探讨在使用平衡Softmax训练后,是否仅通过重训分类器即可降低尾部类别误差。提出两阶段方法BS-cRT:先用平衡Softmax训练骨干网络与余弦分类器,冻结骨干,再在均衡的突发批次上仅更新分类器。第二阶段保持经验先验的平衡Softmax目标,并在推理时使用原始余弦logits。在CIFAR-100-LT、CIFAR-10-LT、ImageNet-LT和Places-LT上,该分类器仅重训步骤均显著提升少样本准确率。在不平衡因子为100时,CIFAR-100-LT上少样本准确率提升+5.15点,CIFAR-10-LT上+5.83点;ImageNet-LT和Places-LT分别提升+6.92和+9.78点,且在ImageNet-LT上存在Top-1与少样本准确率的权衡。进一步分析反事实边界风险最小化(CBRM)发现:缩放后的logit余弦边界会引发训练不稳定,修正后的最难负样本探测仍受头部类别锚定。结果表明BS-cRT是实用的分类器侧基线,边界监督必须考虑类别频率影响。

原文摘要 · Abstract (English)

Long-tailed recognition methods often modify losses, margins, or representations to reduce the dominance of frequent classes. We ask whether, after Balanced Softmax training, the remaining tail error can be reduced by retraining only the classifier. We evaluate BS-cRT, a two-stage procedure that trains a backbone and cosine classifier with Balanced Softmax, freezes the backbone, and updates only the classifier on balanced episodic batches. The second stage keeps the empirical-prior Balanced Softmax objective and uses raw cosine logits at inference. Across CIFAR-100-LT, CIFAR-10-LT, ImageNet-LT, and Places-LT, this classifier-only step consistently improves Few-shot accuracy over the matched Balanced Softmax checkpoint. At imbalance factor 100, Few-shot gains are +5.15 points on CIFAR-100-LT and +5.83 on CIFAR-10-LT; on ImageNet-LT and Places-LT, gains are +6.92 and +9.78 points, respectively, with a Top-1/Few-shot trade-off on ImageNet-LT. We also analyze Counterfactual Boundary Risk Minimization (CBRM), a boundary-probe extension using prototype-based features near decision boundaries. CBRM identifies two failure modes: scaled-logit cosine margins destabilize training, and corrected hardest-negative probes remain head-class anchored. The results support BS-cRT as a practical classifier-side baseline and indicate that boundary supervision must account for class frequency.

长尾识别分类器重训平衡Softmax少样本

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