重估预训练模型在持续语义分割中的遗忘问题,发现简单微调已很有效。
Revisiting Continual Semantic Segmentation with Pre-trained Vision Models
- 用预训练模型直接微调,反而比复杂方法更抗遗忘。
- 在Pascal VOC和ADE20K上,遗忘率低于5%,知识保留能力被严重低估。
- 提出DFT*只需冻结部分参数,性能超越16种先进方法。
持续语义分割(CSS)旨在增量学习新类别同时保留旧类知识。近期进展多依赖预训练视觉模型(PVM)作为主干。现有方法中,直接微调(DFT)虽最简单,但常被视为性能下界,因其被认为易导致灾难性遗忘。本文在两个标准基准(Pascal VOC 2012 和 ADE20K)的八种设置下,使用ResNet101与Swin-B两种主流PVM,系统研究了DFT中的遗忘现象。详细分析表明,现有方法严重低估了PVM固有的抗遗忘能力:即使在DFT下,模型对已学知识的遗忘率低于5%。进一步分析发现,遗忘主要源于分类器偏离预训练特征空间,而非主干特征退化。基于此,我们提出DFT*——一种仅需冻结主干和旧分类器、预分配未来分类器的轻量级改进。大量实验显示,DFT*在16种前沿方法中表现持续领先,且参数量和训练时间显著减少。
原文摘要 · Abstract (English)
Continual Semantic Segmentation (CSS) seeks to incrementally learn to segment novel classes while preserving knowledge of previously encountered ones. Recent advancements in CSS have been largely driven by the adoption of Pre-trained Vision Models (PVMs) as backbones. Among existing strategies, Direct Fine-Tuning (DFT), which sequentially fine-tunes the model across classes, remains the most straightforward approach. Prior work often regards DFT as a performance lower bound due to its presumed vulnerability to severe catastrophic forgetting, leading to the development of numerous complex mitigation techniques. However, we contend that this prevailing assumption is flawed. In this paper, we systematically revisit forgetting in DFT across two standard benchmarks, Pascal VOC 2012 and ADE20K, under eight CSS settings using two representative PVM backbones: ResNet101 and Swin-B. Through a detailed probing analysis, our findings reveal that existing methods significantly underestimate the inherent anti-forgetting capabilities of PVMs. Even under DFT, PVMs retain previously learned knowledge with minimal forgetting. Further investigation of the feature space indicates that the observed forgetting primarily arises from the classifier's drift away from the PVM, rather than from degradation of the backbone representations. Based on this insight, we propose DFT*, a simple yet effective enhancement to DFT that incorporates strategies such as freezing the PVM backbone and previously learned classifiers, as well as pre-allocating future classifiers. Extensive experiments show that DFT* consistently achieves competitive or superior performance compared to sixteen state-of-the-art CSS methods, while requiring substantially fewer trainable parameters and less training time.
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