HPL-ESS: Hybrid Pseudo-Labeling for Unsupervised Event-based Semantic Segmentation

Event-based semantic segmentation has gained popularity due to its capability to deal with scenarios under high-speed motion and extreme lighting conditions which cannot be addressed by conventional RGB cameras. Since it is hard to annotate event data previous approaches rely on event-to-image reconstruction to obtain pseudo labels for training. However this will inevitably introduce noise and learning from noisy pseudo labels especially when generated from a single source may reinforce the errors. This drawback is also called confirmation bias in pseudo-labeling. In this paper we propose a novel hybrid pseudo-labeling framework for unsupervised event-based semantic segmentation HPL-ESS to alleviate the influence of noisy pseudo labels. In particular we first employ a plain unsupervised domain adaptation framework as our baseline which can generate a set of pseudo labels through self-training. Then we incorporate offline event-to-image reconstruction into the framework and obtain another set of pseudo labels by predicting segmentation maps on the reconstructed images. A noisy label learning strategy is designed to mix the two sets of pseudo labels and enhance the quality. Moreover we propose a soft prototypical alignment module to further improve the consistency of target domain features. Extensive experiments show that our proposed method outperforms existing state-of-the-art methods by a large margin on the DSEC-Semantic dataset (+5.88% accuracy +10.32% mIoU) which even surpasses several supervised methods.