Deep semi-supervised learning with contrastive learning and partial label propagation for image data

Deep semi-supervised learning is becoming an active research topic because it jointly utilizes labeled and unlabeled samples in training deep neural networks. Recent advances are mainly focused on inductive semi-supervised learning which generally extends supervised algorithms to include unlabeled data. In this paper, we propose CL_PLP, a new transductive deep semi-supervised learning algorithm based on contrastive self-supervised learning and partial label propagation. The proposed method consists of two modules, contrastive self-supervised learning module extracting features from labeled and unlabeled data and partial label propagation module generating confident pseudo-labels through label propagation. For contrastive learning, we propose an improved twins network model by adding multiple projector layers and the contrastive loss term. Meanwhile, we adopt strong and weak data augmentation to increase the diversity of the dataset and the robustness of the model. For the partial label propagation module, we interrupt the label propagation process according to the quality of pseudo-labels and improve the impact of high-quality pseudo-labels. The performance of our algorithm on three standard baseline datasets CIFAR-10, CIFAR-100 and miniImageNet is better than previous state-of-the-art transductive deep semi-supervised learning methods. By transferring our model to the medical COVID19-Xray dataset, it also achieves good performance. Finally, we propose a strategy to integrate our partial label propagation module with inductive semi-supervised learning method, and the results prove that it can further improve their performance and obtain additional high-quality pseudo-labels for the unlabeled data.