1. INTRODUCTION
Face recognition is an enduring hot topic in the computer vision community. Although great progress has been made by recent deep neural networks [1], [2], [3], pose variations still challenge face recognition in many practical applications. To address this challenge, two main categories of methods, i.e., pose-specific methods [4], [5] and pose-normalization methods [6], [7], have been proposed. Pose-specific methods integrate multiple or tree-structured models that are specific for different face poses, while pose-normalization methods try to synthesize a frontal face from a profile and then use the synthesized image for identification. Compared to pose-specific methods, pose-normalization methods not only have achieved better performance on many benchmark datasets [6], [8] but also have additional advantages such as intuition, interpretability, and convenience.