Dual Sampling Based Causal Intervention for Face Anti-Spoofing With Identity Debiasing

Improving generalization to unseen scenarios is one of the greatest challenges in Face Anti-spoofing (FAS). Most previous FAS works focus on domain debiasing to eliminate the distribution discrepancy between training and test data. However, a crucial but usually neglected bias factor is the face identity. Generally, the identity distribution varies across the FAS datasets as the participants in these datasets are from different regions, which will lead to serious identity bias in the cross-dataset FAS tasks. In this work, we resort to causal learning and propose Dual Sampling based Causal Intervention (DSCI) for face anti-spoofing, which improves the generalization of the FAS model by eliminating the identity bias. DSCI treats the bias as a confounder and applies the backdoor adjustment through the proposed dual sampling on the face identity and the FAS feature. Specifically, we first sample the data uniformly on the identity distribution that is obtained by a pretrained face recognition model. By feeding the sampled data into a network, we can get an estimated FAS feature distribution and sample the FAS feature on it. Sampling the FAS feature from a complete estimated distribution can include potential counterfactual features in the training, which effectively expands the training data. The dual sampling process helps the model learn the real causality between the FAS feature and the input liveness, allowing the model to perform more stably across various identity distributions. Extensive experiments demonstrate our proposed method outperforms the state-of-the-art methods on both intra- and cross-dataset evaluations.