I. Introduction
Traditional optical imaging devices require appropriate illumination conditions to work properly, which is difficult to achieve satisfactorily in practical face recognition applications. To combat low illumination at nights or indoors, infrared imaging devices have been widely applied to many automatic face recognition (ARF) systems. The task of infrared-based ARF systems is to match a probe face image taken with the infrared imaging device to a gallery of face images taken with the optical imaging device, which is considered to be an important application of heterogeneous face recognition [1] (also known as cross-modality face recognition). The most challenging issue in heterogeneous face recognition is that face images associated with the same person but taken with different devices may be mismatched due to the great discrepancy between the different image modalities (optical and infrared), which is referred to as modality gap. As illustrated in Fig. 1, the infrared photos are usually blurred, low contrast, and have significantly different gray distribution compared to the optical photos.
Examples of optical and corresponding infrared face images for (a) HFB dataset and (b) CUHK VIS-NIR dataset.