Semi-Supervised Transfer Learning for Convolutional Neural Network Based Chinese Character Recognition

Although transfer learning has aroused researchers' great interest, how to utilize the unlabeled data is still an open and important problem in this area. We propose a novel semi-supervised transfer learning (STL) method by incorporating Multi-Kernel Maximum Mean Discrepancy (MK-MMD) loss into the traditional fine-tuned Convolutional Neural Network (CNN) transfer learning framework for Chinese character recognition. The proposed method includes three steps. First, a CNN model is trained by massive labeled samples in the source domain. Then the CNN model is fine-tuned by a few labeled samples in the target domain. Finally, the CNN model is trained with both a large number of unlabeled samples and the limited labeled samples in the target domain to minimize the MK-MMD loss. Experiments investigate detailed configurations and parameters of the proposed STL method with several frequently used CNN structures including AlexNet, GoogLeNet, and ResNet. Experimental results on practical Chinese character transfer learning tasks, such as Dunhuang historical Chinese character recognition, indicate that the proposed method can significantly improve recognition accuracy in the target domain.