Locating Noise is Halfway Denoising for Semi-Supervised Segmentation.

We investigate semi-supervised semantic segmentation with self-training, where a teacher model generates pseudo masks to exploit the benefits of a large amount of unlabeled images. We notice that the noisy label from the generated pseudo masks is the major obstacle to achieving good performance. Previous works all treat the noise in pixel level and ignore the contextual information of the noise. This work shows that locating the patch-wise noisy region is a better way to deal with noise. To be specific, our method, named Uncertainty-aware Patch CutMix (UPC), first estimates the uncertainty of per-pixel prediction for pseudo masks of unlabeled images. Then UPC splits the uncertainty map into patches and calculates patch-wise uncertainty. UPC selects top-k most uncertain patches to generate the uncertain regions. Finally, uncertain regions are replaced with reliable ones from labeled images. We conduct extensive experiments using standard semi-supervised settings on Pascal VOC and Cityscapes. Experiment results show that UPC can significantly boost the performance of the state-of-the-art methods. In addition, we further demonstrate that our UPC is robust to out-of-distribution unlabeled images, e.g., MSCOCO.