GEN: Pushing the Limits of Softmax-Based Out-of-Distribution Detection

Out-of-distribution (OOD) detection has been exten-sively studied in order to successfully deploy neural networks, in particular, for safety-critical applications. More-over, performing OOD detection on large-scale datasets is closer to reality, but is also more challenging. Sev-eral approaches need to either access the training data for score design or expose models to outliers during training. Some post-hoc methods are able to avoid the afore-mentioned constraints, but are less competitive. In this work, we propose Generalized ENtropy score (GEN), a simple but effective entropy-based score function, which can be applied to any pre-trained softmax-based classifier. Its performance is demonstrated on the large-scale ImageNet-lk OOD detection benchmark. It consistently improves the average AUROC across six commonly-used CNN-based and visual transformer classifiers over a num-ber of state-of-the-art post-hoc methods. The average AU- ROC improvement is at least 3.5%. Furthermore, we used GEN on top of feature-based enhancing methods as well as methods using training statistics to further improve the OOD detection performance. The code is available at: https://github.com/XixiLiu95/GEN.