Learning inter-class optical flow difference using generative adversarial networks for facial expression recognition

Facial expression recognition is a fine-grained task because different emotions have subtle facial movements. This paper proposes to learn inter-class optical flow difference using generative adversarial networks (GANs) for facial expression recognition. Initially, the proposed method employs a GAN to produce inter-class optical flow images from the difference between the static fully expressive samples and neutral expression samples. Such inter-class optical flow difference is used to highlight the displacement of facial parts between the neutral facial images and fully expressive facial images, which can avoid the disadvantage that the optical flow change between adjacent frames of the same video expression image is not obvious. Then, the proposed method designs four-channel convolutional neural networks (CNNs) to learn high-level optical flow features from the produced inter-class optical flow images, and high-level static appearance features from the fully expressive facial images, respectively. Finally, a decision-level fusion strategy is adopted to implement facial expression classification. The proposed method is validated on two public facial expression databases, BAUM_1a, SAMM and AFEW5.0, demonstrating its promising performance.