用批评者模型修正分类器过自信问题,提升准确率与校准性。
Critic Loss for Image Classification
- 构建生成器-批评者框架,让批评者评估分类器输出可靠性。
- 在少量标签数据下显著提升分类器泛化能力与校准性。
- 适合半监督学习和主动学习场景,可自动筛选待标注数据。
现代神经网络分类器在各类任务中表现优异,但常因交叉熵损失导致预测过自信。为此,我们提出图像分类的批评者损失(CrtCl)。该方法将基础分类器视为生成器,输出类别概率分布与中间特征;引入一个不依赖真实标签的批评者模型,基于图像、中间特征及分类结果判断分类正确概率,并反向传播作为自监督信号。批评者无需标签,可在半监督学习中同时利用有标签与无标签数据。CrtCl是一种可学习的损失函数,能缓解交叉熵带来的负面效应。此外,它还可用于主动学习中估计未标记数据的分类能力,指导标注选择。我们在低标签数据和主动学习场景下验证了有效性,结果显示:在三个图像分类数据集上,相比近期基线,CrtCl均提升了分类器的泛化能力与校准性。
原文摘要 · Abstract (English)
Modern neural network classifiers achieve remarkable performance across a variety of tasks; however, they frequently exhibit overconfidence in their predictions due to the cross-entropy loss. Inspired by this problem, we propose the \textbf{Cr}i\textbf{t}ic Loss for Image \textbf{Cl}assification (CrtCl, pronounced Critical). CrtCl formulates image classification training in a generator-critic framework, with a base classifier acting as a generator, and a correctness critic imposing a loss on the classifier. The base classifier, acting as the generator, given images, generates the probability distribution over classes and intermediate embeddings. The critic model, given the image, intermediate embeddings, and output predictions of the base model, predicts the probability that the base model has produced the correct classification, which then can be back propagated as a self supervision signal. Notably, the critic does not use the label as input, meaning that the critic can train the base model on both labeled and unlabeled data in semi-supervised learning settings. CrtCl represents a learned loss method for accuracy, alleviating the negative side effects of using cross-entropy loss. Additionally, CrtCl provides a powerful way to select data to be labeled in an active learning setting, by estimating the classification ability of the base model on unlabeled data. We study the effectiveness of CrtCl in low-labeled data regimes, and in the context of active learning. In classification, we find that CrtCl, compared to recent baselines, increases classifier generalization and calibration with various amounts of labeled data. In active learning, we show our method outperforms baselines in accuracy and calibration. We observe consistent results across three image classification datasets.
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