Facial expression recognition boosted by soft label with a diverse ensemble

Facial expression recognition (FER) has recently attracted increasing attention with its growing applications in human-computer interaction and other fields. But a well-performing convolutional neural network (CNN) model learned using hard label/single-emotion label supervision may not obtain optimal performance in real-life applications because captured facial images usually exhibit expression as a mixture of multiple emotions instead of a single emotion. To address this problem, this paper presents a novel FER framework using a CNN and soft label that associates multiple emotions with each expression. In this framework, the soft label is obtained using a proposed constructor, which mainly involves two steps: (1) training a CNN model on a training set using hard label supervision; (2) fusing the latent label probability distribution predicted by the trained model to obtain soft labels. To improve the generalization performance of the ensemble classifier, we propose a novel label-level perturbation strategy to train multiple base classifiers with diversity. Experiments have been carried out on 3 publicly available databases: FER-2013, SFEW and RAF. The results indicate that our method achieves competitive or even better performance (FER-2013: 73.73%, SFEW: 55.73%, RAF: 86.31%) compared to state-of-the-art methods. (C) 2019 Published by Elsevier B.V.