Yihan Xu

Existing facial expression recognition (FER) methods typically fine-tune a pre-trained visual encoder using discrete labels. However, this form of supervision limits to specify the emotional concept of different facial expressions. In this paper, we observe that the rich knowledge in text embeddings, generated by vision-language models, is a promising alternative for learning discriminative facial expression representations. Inspired by this, we propose a novel knowledge-enhanced FER method with an emotional-to-neutral transformation. Specifically, we formulate the FER problem as a process to match the similarity between a facial expression representation and text embeddings. Then, we transform the facial expression representation to a neutral representation by simulating the difference in text embeddings from textual facial expression to textual neutral. Finally, a self-contrast objective is introduced to pull the facial expression representation closer to the textual facial expression, while pushing it farther from the neutral representation. We conduct evaluation with diverse pre-trained visual encoders including ResNet-18 and Swin-T on four challenging facial expression datasets. Extensive experiments demonstrate that our method significantly outperforms state-of-the-art FER methods. The code is made publicly available at https://github.com/hangyu94/KE2NT.

Semi-supervised learning (SSL) has proven effective in assigning a pseudo-label to a confident sample whose largest class probability is above a fixed threshold. However, in the context of semi-supervised facial attribute recognition (SSFAR), where a sample is associated with multiple presence and absence pseudo-labels, directly applying existing SSL methods is challenging due to two issues: 1) the lack of a clear boundary between presence and absence predictions for an attribute makes it difficult to distinguish them using a single threshold; 2) the learning difficulty varies across attributes, so the fixed strategy fails to adaptively learn different attributes. To address these challenges, we propose Dynamic thrEShold Pairs (DESP), a simple yet effective method to handle the SSFAR problem. Specifically, during each training stage, we derive two sets for each attribute from labeled samples, which contain the predicted probabilities of presence and absence, respectively. We then compute the mid-ranges of the two sets as paired presence and absence thresholds. Finally, we assign a presence or absence pseudo-label for the attribute to an unlabeled sample when its prediction exceeds the presence threshold or falls below the absence threshold. Extensive experiments on the CelebA and LFWA datasets demonstrate that DESP achieves superior performance compared to state-of-the-art methods, especially in the case of scarce labeled samples. Also, DESP performs well on multi-label datasets such as Pascal VOC and MS-COCO. The code will be publicly available at https://github.com/yihanxxu/DESP.