POST: Prototype-oriented similarity transfer framework for cross-domain facial expression recognition

Facial expression recognition (FER) is one of the popular research topics in computer vision. Most deep learning expression recognition methods perform well on a single dataset, but may struggle in cross-domain FER applications when applied to different datasets. FER under cross-dataset also suffers from difficulties such as feature distribution deviation and discriminator degradation. To address these issues, we propose a prototype-oriented similarity transfer framework (POST) for cross-domain FER. The bidirectional cross-attention Swin Transformer (BCS Transformer) module is designed to aggregate local facial feature similarities across different domains, enabling the extraction of relevant cross-domain features. The dual learnable category prototypes is designed to represent potential space samples for both source and target domains, ensuring enhanced domain alignment by leveraging both cross-domain and specific domain features. We further introduce the self-training resampling (STR) strategy to enhance similarity transfer. The experimental results with the RAF-DB dataset as the source domain and the CK+, FER2013, JAFFE and SFEW 2.0 datasets as the target domains, show that our approach achieves much higher performance than the state-of-the-art cross-domain FER methods.