Hand-vein biometrics as a high-security pattern has received more and more attention. One of the open issues in hand-vein verification is the lack of robustness against image quality degradation, which may comprise the verification accuracy. To achieve robust verification, vein feature extraction approaches, especially vein texture segmentation, have been extensively investigated. In recent years, deep neural networks have achieved promising results in medical image segmentation and have been brought into vein verification, but current solutions suffer from two challenges for vein segmentation: 1) lacking the labeling data, which is expensive to obtain and 2) the incorrect label data obtained by manual labeling scheme or automatic labeling scheme may strongly influence parameters when the network is trained, which may degrade the verification performance. This paper proposes an iterative deep belief network (DBN) to extract vein features based on the initial label data, which are automatically generated using a very limited a priori knowledge and iteratively corrected by our DBN. First, a known handcrafted vein image segmentation technique is employed to automatically label vein pixel and background pixel. A training dataset is constructed based on the patches centered on the labeled pixels. Second, a DBN is trained on the resulting database to predict the probability of each pixel to belong to be a vein pixel given a patch centered on it. The vein patterns are segmented using a probability threshold of 0.5. The resulting vein features are employed to reconstruct the training dataset, based on which the network is retrained. During the iterative procedure, the incorrect labels of training data are statistically corrected, which enables DBN to effectively learn what a finger-vein pattern is by learning the difference between vein patterns and background ones. The experimental results on two public hand-vein databases show a significant improvement in terms of hand-vein verification accuracy. INDEX TERMS Hand biometrics, palm-vein verification, deep learning, iterative deep neural network, representation learning. I. INTRODUCTION With the tremendous ubiquity of Internet and increasing security awareness, traditional authentication, such as passwords, personal identification numbers, smart cards, is hard to meet the requirements of convenience, reliability, and security in practical applications. For example, passwords are easy to forgot, and smart cards are easily lost, copied and forged. Under such circumstances, automatic personal verification using physiological and/or behavioral characteristics The associate editor coordinating the review of this manuscript and approving it for publication was Kashif Munir. of humans, has received increasing attention. Currently, various biometrics characteristics have been investigated and applied in practical life. Broadly, they can be categorized in two categories: (1) extrinsic biometric features, i.e. face [1], fingerprint [2], iris [3], palmprint [4], hand shape [5], and ...
