A spatio-temporal integrated model based on local and global features for video expression recognition

Facial expressions can be represented largely by the dynamic variations of important facial expression parts, i.e., eyebrows, eyes, nose, and mouth. The features of these parts are regarded as local features. However, facial global information is also useful for recognition because it is a necessary complement to local features. In this paper, a spatio-temporal integrated model that jointly learns local and global features is proposed for video expression recognition. Firstly, to capture the action of facial key units, a spatio-temporal attention part-gradient-based hierarchical bidirectional recurrent neural network (spatio-temporal attention PGHRNN) is constructed. It can capture the dynamic variations of gradients around facial landmark points. In addition, a new kind of spatial attention mechanism is introduced to recalibrate the features of facial various parts adaptively. Secondly, to complement the local features extracted by the spatio-temporal attention PGHRNN, a squeeze-and-excitation residual network of 50 layers with long short-term memory network (SE-ResNet-50-LSTM) is used as a global feature extractor and classifier. Finally, to integrate the local and global features and improve the performance of facial expression recognition, a joint adaptive fine-tuning method (JAFTM) is proposed to combine the two networks, which can adaptively adjust the network weights. Extensive experiments demonstrate that our proposed model can achieve a superior recognition accuracy of 98.95% on CK + for 7-class facial expressions and 85.40% on MMI database, which outperforms other state-of-the-art methods.