Unbiased Feature Learning with Causal Intervention for Visible-Infrared Person Re-Identification

Visible-infrared person re-identification (VI-ReID) aims to match individuals across different modalities. Existing methods can learn class-separable features but still struggle with modality gaps within class due to the modality-specific information, which is discriminative in one modality but not present in another (e.g., a black striped shirt). The presence of the interfering information creates a spurious correlation with the class label, which hinders alignment across modalities. To this end, we propose an Unbiased feature learning method based on Causal inTervention for VI-ReID from three aspects. Firstly, through the proposed structural causal graph, we demonstrate that modality-specific information acts as a confounder that restricts the intra-class feature alignment. Secondly, we propose a causal intervention method to remove the confounder using an effective approximation of backdoor adjustment, which involves adjusting the spurious correlation between features and labels. Thirdly, we incorporate the proposed approximation method into the basic VI-ReID model. Specifically, the confounder can be removed by adjusting the extracted features with a set of weighted pre-trained class prototypes from different modalities, where the weight is adapted based on the features. Extensive experiments on the SYSU-MM01 and RegDB datasets demonstrate that our method outperforms state-of-the-art methods. Code is available at https://github.com/NJUPT-MCC/UCT.