WDAN: A Weighted Discriminative Adversarial Network With Dual Classifiers for Fine-Grained Open-Set Domain Adaptation

Deep neural networks usually depend on substantial labeled data and suffer from poor generalization to new domains. Domain adaptation can be used to resolve these issues, using a classifier trained with a label-rich source and transferred to a label-scarce target domain. Traditional domain adaptation adopts the close-set assumption that both domains share the same classes. However, real-world applications operate in an open-set scenario where target domains have private categories. This aspect is considered by open-set domain adaptation (OSDA). Nevertheless, current OSDA benchmarks lack clear definitions of semantic classes that are at the core of the open-set concept. In this study, we propose fine-grained visual categorization (FGVC) datasets containing specific descriptions of semantic classes as a solution, introducing the new setting named fine-grained OSDA. Owing to the entanglement among FGVC, unknown class recognition, and domain adaptation, fine-grained OSDA is a challenging task. For this reason, we designed a weighted discriminative adversarial network with dual classifiers (WDAN). It utilizes a selective transformer encoder with overlapping patches and supervised contrastive learning to extract features suitable for FGVC, adversarial training with domain-specific discriminative information to recognize target-private classes, and a weighted conditional domain discriminator to learn domain-invariant features for domain adaptation. Extensive experiments on five benchmarks, including one newly built, demonstrated that WDAN outperforms state-of-the-art methods. This work fills the existing gap in benchmarks for fine-grained OSDA, promoting future developments of real-world applications.