I. Introduction
Face recognition has been one of the most widely researched topics in computer vision for decades. With the rise of deep learning techniques and the growth in the size of internet data, face recognition methods achieve excellent performance in ’in the wild’ conditions. Supported by better depth models [1], [2], [3], more accurate loss constraints [4], [5], [6] and larger scale training data [7], [8], [9], current face recognition methods almost outperform humans on major benchmarks. However, in some extreme cases, this remains a challenging task. To date, how to effectively overcome image acquisition perspective and face pose variation is still a hot research topic, and it is the key bottleneck that has the greatest impact on face recognition performance in many real-world scenarios.