Universal Domain Adaptation (UNDA) aims to handle both domain-shift and
category-shift between two datasets, where the main challenge is to transfer
knowledge while rejecting unknown classes which are absent in the labeled
source data but present in the unlabeled target data. Existing methods manually
set a threshold to reject unknown samples based on validation or a pre-defined
ratio of unknown samples, but this strategy is not practical. In this paper, we
propose a method to learn the threshold using source samples and to adapt it to
the target domain. Our idea is that a minimum inter-class distance in the
source domain should be a good threshold to decide between known or unknown in
the target. To learn the inter-and intra-class distance, we propose to train a
one-vs-all classifier for each class using labeled source data. Then, we adapt
the open-set classifier to the target domain by minimizing class entropy. The
resulting framework is the simplest of all baselines of UNDA and is insensitive
to the value of a hyper-parameter yet outperforms baselines with a large
margin.

本文介绍一种使用最小类间距离阈值的通用领域适应（UNDA）方法，该方法使用源样本学习该阈值并将其适应于目标领域，同时训练一种基于一对所有分类器的学习方法。