Facial Action Coding System (FACS) - A Visual Guidebook

Facial Action Coding System - Wikipedia

Definition

Facial Action Coding System(FACS) is a system to taxonomize human facial movements by their appearance on the face.

Movements of individual facial muscles are encoded by FACS from slight different instant changes in facial appearance.

FACS detects faces in videos, extracts the geometrical features of the faces, and then produces temporal profiles of each facial movement.

Uses

Using FACS human coders can manually code nearly any anatomically possible facial expression, deconstructing it into the specific action units (AU) and their temporal segments that produced the expression.

AUs are a contraction or relaxation of one or more muscles. It also defines a number of Action Descriptors, which differ from AUs in that the authors of FACS have not specified the muscular basis for the action and have not distinguished specific behaviors as precisely as they have for the AUs.

For example, FACS can be used to distinguish two types of smiles as follows:

• Insincere and voluntary Pan-Am smile: contraction of zygomatic major alone
• Sincere and involuntary Duchenne smile: contraction of zygomatic major and inferior part of orbicularis oculi.

Expression list

Codes for action units

FACS is an index of facial expressions, but does not actually provide any biomechanical information about the degree of muscle activation.