Category Dictionary Guided Unsupervised Domain Adaptation for Object Detection

Unsupervised domain adaption (UDA) is a promising solution to enhance the generalization ability of a model from a source domain to a target domain without manually annotating labels for the target data. Recent works in cross-domain object detection mostly resort to adversarial feature adaptation to match the marginal distributions of two domains. However, perfect feature alignment is hard to achieve and what's more is likely to cause negative transfer due to the high complexity of object detection. In this paper, we take a different approach to reduce the domain gap by a selftraining paradigm, which regards the pseudo-labels as ground truth to fully exploit the unlabeled target data. In order to generate more informative pseudo labels, we further propose a category dictionary guided (CDG) UDA model for crossdomain object detection, which learns category-specific dictionaries from the source domain to represent the candidate boxes in target domain. The representation residual can be used for not only pseudo label assignment but also quality (e.g., IoU) estimation of the candidate box. Compared with decision boundary based classifiers such as softmax, the proposed CDG scheme can select more informative and reliable pseudo-boxes. Experimental results on benchmark datasets show that the proposed CDG significantly exceeds the stateof-the-arts in cross-domain object detection.