With the increasing demand for multi-view face recognition techniques

frontal face image synthesis has been one of the most interesting research topics nowadays. However

it is a classic inverse problem to synthesize frontal images from profiles accurately

and there are some challenges.In this paper

we present a systematical summary of the current frontal image synthesis methods.Furthermore

some classic synthesis strategies are introduced. Moreover

according to the theories used

the methods are classified into two categories:graphic based methods and statistical learning based methods. Additionally

these approaches are compared in three aspects: complicacy

robustness

and performance. At last

some potential pointers towards future research topics are given.