Two Losses, One Goal: Balancing Conflict Gradients for Semi-supervised Semantic Segmentation

Semi-supervised semantic segmentation has attracted considerable attention as it alleviates the need for extensive pixel-level annotations. However, existing methods often overlook the potential optimization conflict between supervised and unsupervised learning objectives, leading to suboptimal performance. In this paper, we identify this under-explored issue and propose a novel Pareto Optimization Strategy (POS) to tackle it. POS aims to find a descent gradient direction that benefits both learning objectives, thereby facilitating model training. By dynamically assigning weights to the gradients at each iteration based on the model's learning status, POS effectively reconciles the intrinsic tension between the two objectives. Furthermore, we analyze POS from the perspective of gradient descent in random batch sampling and propose the Magnitude Enhancement Operation (MEO) to further unleash its potential by considering both direction and magnitude during gradient integration. Extensive experiments on challenging benchmarks demonstrate that integrating POS into existing semi-supervised segmentation methods yields consistent improvements across different data splits and architectures (CNN, Transformer), showcasing its effectiveness.