Automatic facial expression recognition is an interesting and challenging problem and has several important applications in many areas such as human-computer interaction, human behavior understanding, and data-driven animation. Unlike face recognition, facial expression recognition needs to discriminate between the same expression in different individuals. The problem becomes more difficult as a person may show the same expression in different ways.

The current existing approaches for measuring facial expressions can be categorized into two types: static image and image sequence. In the static image approach, the system analyzes the facial expression in each image frame separately. In the image sequence approach, the system tries to capture the temporal pattern of the motion and changes seen on the face in the sequence of image frames. Recently, attention has been shifted toward the image sequence approach. However, this approach is more difficult...