A Deeper Look at Facial Expression Dataset Bias

Datasets play an important role in the progress of facial expression recognition algorithms, but they may suffer from obvious biases caused by different cultures and collection conditions. To look deeper into this bias, we first conduct comprehensive experiments on dataset recognition and cross-dataset generalization tasks, and for the first time, explore the intrinsic causes of the dataset discrepancy. The results quantitatively verify that current datasets have a strong build-in bias, and corresponding analyses indicate that the conditional probability distributions between source and target datasets are different. However, previous researches are mainly based on shallow features with limited discriminative ability under the assumption that the conditional distribution remains unchanged across domains. To address these issues, we further propose a novel deep Emotion-Conditional Adaption Network (ECAN) to learn domain-invariant and discriminative feature representations, which can match not only the marginal distribution but also the class-conditional distribution across domains by exploring the underlying label information of the target dataset. Moreover, the largely ignored expression class distribution bias is also addressed so that the training and testing domains can share similar class distribution. Extensive cross-database experiments on both lab-controlled datasets (CK+, JAFFE, MMI, and Oulu-CASIA) and real-world databases (AffectNet, FER2013, RAF-DB 2.0, and SFEW 2.0) demonstrate that our ECAN can yield competitive performances across various cross-dataset facial expression recognition tasks and outperform the state-of-the-art methods.