A Survey of Unsupervised Domain Adaptation for Visual Recognition

TL;DR

This survey reviews unsupervised domain adaptation techniques for visual recognition, highlighting methods to reduce domain shift without labeled target data, and summarizes benchmark performances.

Contribution

It provides a comprehensive overview of traditional and deep learning-based UDA methods and compiles benchmark results for visual recognition tasks.

Findings

Deep learning methods outperform traditional approaches.

Benchmark datasets reveal current state-of-the-art performance.

UDA effectively reduces domain discrepancy in visual recognition.

Abstract

While huge volumes of unlabeled data are generated and made available in many domains, the demand for automated understanding of visual data is higher than ever before. Most existing machine learning models typically rely on massive amounts of labeled training data to achieve high performance. Unfortunately, such a requirement cannot be met in real-world applications. The number of labels is limited and manually annotating data is expensive and time-consuming. It is often necessary to transfer knowledge from an existing labeled domain to a new domain. However, model performance degrades because of the differences between domains (domain shift or dataset bias). To overcome the burden of annotation, Domain Adaptation (DA) aims to mitigate the domain shift problem when transferring knowledge from one domain into another similar but different domain. Unsupervised DA (UDA) deals with a labeled source domain and an unlabeled target domain. The principal objective of UDA is to reduce the domain discrepancy between the labeled source data and unlabeled target data and to learn domain-invariant representations across the two domains during training. In this paper, we first define UDA problem. Secondly, we overview the state-of-the-art methods for different categories of UDA from both traditional methods and deep learning based methods. Finally, we collect frequently used benchmark datasets and report results of the state-of-the-art methods of UDA on visual recognition problem.