1. INTRODUCTION
Although current 2D image face recognition systems have reached a certain level of maturity, the performance of these systems has been limited by external conditions such as pose, expression and illumination. Especially, the influence of varying ambient illumination on the subject is known to be one of the major confounding factors for visual face recognition [1]. To alleviate these conditions, 3D sensor-based or infra-red (IR) sensor-based methods have recently received significant attention [2] [3] [4]. The IR-based method particularly showed very good performance in an illumination variation environment [2]. Also, the IR-based method has been proved to be very robust in terms of expression variation [3]. On the other hand, a weakness of the IR-based method is that variations in environmental conditions like temperature or wind can cause similar problems to changes in illumination do for visual images.