Active learning typically focuses on training a model on few labeled examples alone, while unlabeled ones are only used for acquisition. In this work we depart from this setting by using both labeled and unlabeled data during model training across active learning cycles. We do so by using unsupervised feature learning at the beginning of the active learning pipeline and semi-supervised learning at every active learning cycle, on all available data. The former has not been investigated before in active learning, while the study of latter in the context of deep learning is scarce and recent findings are not conclusive with respect to its benefit. Our idea is orthogonal to acquisition strategies by using more data, much like ensemble methods use more models. By systematically evaluating on a number of popular acquisition strategies and datasets, we find that the use of unlabeled data during model training brings a surprising accuracy improvement in image classification, compared to the differences between acquisition strategies. We thus explore smaller label budgets, even one label per class.

该研究提出了在主动学习的过程中既利用有标签的数据，也利用无标签的数据进行模型训练的方法，并使用了无监督特征学习和半监督学习的技术，研究表明使用无标签数据进行模型训练在图像分类任务中可以带来比不同获取策略更高的准确度，因此可以得到更小的标签预算。

深度主动学习反思：在模型训练中利用未标记数据