Novel Class Discovery in Semantic Segmentation

We introduce a new setting of Novel Class Discovery in Semantic Segmentation (NCDSS), which aims at segmenting unlabeled images containing new classes given prior knowledge from a labeled set of disjoint classes. In contrast to existing approaches that look at novel class dis-covery in image classification, we focus on the more chal-lenging semantic segmentation. In NCDSS, we need to dis-tinguish the objects and background, and to handle the existence of multiple classes within an image, which in-creases the difficulty in using the unlabeled data. To tackle this new setting, we leverage the labeled base data and a saliency model to coarsely cluster novel classes for model training in our basic framework. Additionally, we propose the Entropy-based Uncertainty Modeling and Self-training (EUMS) framework to overcome noisy pseudo-labels, fur-ther improving the model performance on the novel classes. Our EUMS utilizes an entropy ranking technique and a dy-namic reassignment to distill clean labels, thereby making full use of the noisy data via self-supervised learning. We build the NCDSS benchmark on the PASCAL-5i dataset and COCO-20i dataset. Extensive experiments demonstrate the feasibility of the basic framework (achieving an average mIoU of 49.81% on PASCAL-5i) and the effectiveness of EUMS framework (outperforming the basic framework by 9.28% mIoU on PASCAL-5i).