SFC: Shared Feature Calibration in Weakly Supervised Semantic Segmentation

Image-level weakly supervised semantic segmentation has received increasing attention due to its low annotation cost.Existing methods mainly rely on Class Activation Mapping (CAM) to obtain pseudo-labels for training semantic segmentation models.In this work, we are the first to demonstrate that long-tailed distribution in training data can cause the CAM calculated through classifier weights over-activated for head classes and under-activated for tail classes due to the shared features among head-and tail-classes.This degrades pseudo-label quality and further influences final semantic segmentation performance.To address this issue, we propose a Shared Feature Calibration (SFC) method for CAM generation.Specifically, we leverage the class prototypes that carry positive shared features and propose a Multi-Scaled Distribution-Weighted (MSDW) consistency loss for narrowing the gap between the CAMs generated through classifier weights and class prototypes during training.The MSDW loss counterbalances over-activation and under-activation by calibrating the shared features in head-/tail-class classifier weights.Experimental results show that our SFC significantly improves CAM boundaries and achieves new state-of-the-art performances.The project is available at https://github.com/Barrett-python/SFC.