Federated Hallucination Translation and Source-Free Regularization Adaptation in Decentralized Domain Adaptation for Foggy Scene Understanding

Semantic foggy scene understanding (SFSU) emerges a challenging task under out-of-domain distribution (OD) due to uncertain cognition caused by degraded visibility. With the strong assumption of data centralization, unsupervised domain adaptation (UDA) reduces vulnerability under OD scenario. Whereas, enlarged domain gap and growing privacy concern heavily challenge conventional UDA. Motivated by gap decomposition and data decentralization, we establish a decentralized domain adaptation (DDA) framework called Translate thEn Adapt (abbr. TEA) for privacy preservation. Our highlights lie in. (1) Regarding federated hallucination translation, a Disentanglement and Contrastive-learning based Generative Adversarial Network (abbr. DisCoGAN) is proposed to impose contrastive prior and disentangle latent space in cycle-consistent translation. To yield domain hallucination, client minimizes cross-entropy of local classifier but maximizes entropy of global model to train translator. (2) Regarding source-free regularization adaptation, a Prototypical-knowledge based Regularization Adaptation (abbr. ProRA) is presented to align joint distribution in output space. Soft adversarial learning relaxes binary label to rectify inter-domain discrepancy and inner-domain divergence. Structure clustering and entropy minimization drive intra-class features closer and inter-class features apart. Extensive experiments exhibit efficacy of our TEA which achieves 55.26% or 46.25% mIoU in adaptation from GTA5 to Foggy Cityscapes or Foggy Zurich, outperforming other DDA methods for SFSU.