Strengthen Out-of-Distribution Detection via Adaptive Mahalanobis Gap

Deep neural networks have achieved significant success on in-distribution (ID) tasks, but out-of-distribution (OOD) samples during inference can lead to unreliable predictions. To address this issue, distance-based methods exploit the geometric structure of feature space for OOD detection. However, methods based on static information geometry fail to address geometry distorted by ill-distributed samples. Although prior work reduces the misclassification of OOD samples as ID by adjusting the residual space with real-time features, it fails to address the misclassification of ID samples as OOD. In addition, existing distance-based methods ignore class-specific characteristics when computing deviation feature and rely on the nearest prototype for uncertainty estimation, leading to suboptimal OOD detection performance. To address these issues, we propose Adaptive Mahalanobis Gap (AMG). Specifically, we first strengthen the principal space along real-time feature directions to reduce the misclassification of ID samples as OOD. Subsequently, we incorporate class variance and prototype norms to mitigate bias of deviation feature from class-wise distributional differences. Finally, we introduce the Mahalanobis gap scoring for uncertainty scoring to overcome bias from single-prototype reliance. Experiments on CIFAR-10/100 and ImageNet-1k show that AMG consistently outperforms state-of-the-art methods in FPR@95 and AUROC. Our code is available at https://anonymous.4open.science/r/AMG_AR.