Modeling Uncertainty for Low-Resolution Facial Expression Recognition

Recently, facial expression recognition techniques have made significant progress on high-resolution web images. However, in real-world applications, the obtained images are often with low resolution since they are mostly captured in a wide range of public spaces. As a result, the ambiguity of the expression labels hinders recognition performance due to not only subjective emotion annotations but also ambiguous images. Existing approaches tend to perform poorly when the resolution of face images decreases. In this work, we aim to model the aleatoric uncertainty induced by low-image-resolution and label ambiguity for robust facial expression recognition. We propose probabilistic data uncertainty learning to capture the ambiguity induced by poor image resolution. Additionally, we introduce the emotion wheel to learn the label-uncertainty-aware embedding. Moreover, we exploit the ambiguous nature of neutrality and propose a neutral expression constraint to learn more robust features for facial expression recognition. To the best of our knowledge, this is the first work utilizing the intrinsic nature of neutrality as a regularization to benefit model training. Extensive experimental results show the effectiveness and robustness of our approach. Under low-resolution conditions, our proposed method outperforms the state-of-the-art approaches by 3.02% and 3.16% in terms of accuracy on RAF-DB and FERPlus, respectively.