Unsupervised domain translation (UDT) is often realized by generative adversarial network (GAN)-based probability distribution matching of the source and target domains. CycleGAN stands as arguably the most representative approach among this line of work. However, it was noticed in recent works that CycleGAN and variants could fail to identify the desired translation function and produce content-misaligned translations. This limitation arises due to the presence of multiple translation functions---referred to as ``measure-preserving automorphism" (MPA)---in the solution space of the learning criteria. Despite the awareness of such identifiability issues, solutions have remained elusive. This study delves into the core identifiability challenge and introduces an MPA elimination theory. Our analysis shows that MPA is unlikely to exist, if multiple pairs of diverse cross-domain conditional distributions are aligned by the learning criterion. Our theory leads to a UDT learner using distribution matching over auxiliary variable-induced subsets of the domains---other than over the entire source/target domains as in the classical setting. The proposed framework is the first to rigorously establish identifiability of the desired translation function for UDT, to our best knowledge. Experiments corroborate with our theoretical claims.
Towards Identifiable Unsupervised Domain Translation: A Diversified Distribution Matching Approach
Sagar Shrestha Xiao Fu