1 Introduction

How to synthesize photorealistic images of human faces has been a fascinating yet difficult problem in computer graphics. Here, the term "face synthesis" refers to synthesis of still images as well as synthesis of facial animations. In general, it is difficult to draw a clean line between the synthesis of still images and that of facial animations. For example, the technique of synthesizing facial expression images can be directly used for generating facial animations, and most of the facial animation systems involve the synthesis of still images. In this chapter, we focus more on the synthesis of still images and skip most of the aspects that mainly involve the motion over time.

Face synthesis has many interesting applications. In the film industry, people would like to create virtual human characters that are indistinguishable from the real ones. In games, people have been trying to create human characters that are interactive and realistic. There are commercially available products [15, 16] that allow people to create realistic looking avatars that can be used in chatting rooms, e-mail, greeting cards, and teleconferencing. Many human-machine dialog systems use realistic-looking human faces as visual representation of the computer agent that interacts with the human user. Face synthesis techniques have also been used for talking head compression in the video conferencing scenario.

The techniques of face synthesis can be useful for face recognition too. Romdhani et al. [35] used their three dimensional (3D) face modeling technique...