Facial Recognition Algorithms:

Algorithms vary in the process of transformation (feature extraction) and matching (recognition). According to present developments algorithms are classified as Image based and Video based. Research is going on for the video based approach that enables recognizing humans from real surveillance videos.

The traditional predominant algorithms are based on either of the two basic approaches namely,

• Geometric (feature based)
• Photometric (view based)

The geometrical approach is based on geometrical relationship between facial landmarks, or in other words the spatial configuration of facial features. That means that the main geometrical features of the face such as the eyes, nose and mouth are first located and then faces are classified on the basis of various geometrical distances and angles between features. The limitation of this approach is that it is entirely based on detection of the landmarks, which may be difficult in case of pose variations, shadows and varying illumination. 

On the other hand, the pictorial approach is based on the photometric characteristics of image. The method employs the templates of the major facial features and entire face to perform recognition on frontal views of faces.

 Apart from these two techniques we have other recent template-based approaches, which form templates from the image gradient, and the principal component analysis approach, which can be read as a sub-optimal template approach. Finally we have the deformable template approach that combines elements of both the pictorial and feature geometry approaches and has been applied to faces at varying pose and expression.