  Deep learning applies multiple processing layers to learn representations of
data with multiple levels of feature extraction. This emerging technique has
reshaped the research landscape of face recognition (FR) since 2014, launched
by the breakthroughs of DeepFace and DeepID. Since then, deep learning
technique, characterized by the hierarchical architecture to stitch together
pixels into invariant face representation, has dramatically improved the
state-of-the-art performance and fostered successful real-world applications.
In this survey, we provide a comprehensive review of the recent developments on
deep FR, covering broad topics on algorithm designs, databases, protocols, and
application scenes. First, we summarize different network architectures and
loss functions proposed in the rapid evolution of the deep FR methods. Second,
the related face processing methods are categorized into two classes:
"one-to-many augmentation" and "many-to-one normalization". Then, we summarize
and compare the commonly used databases for both model training and evaluation.
Third, we review miscellaneous scenes in deep FR, such as cross-factor,
heterogenous, multiple-media and industrial scenes. Finally, the technical
challenges and several promising directions are highlighted.
