The Facial Action Coding System (FACS) is a system to taxonomize human facial movements by their appearance on the face, based on a system originally developed by a Swedish anatomist named Carl-Herman Hjortsjö. It was later adopted by Paul Ekman and Wallace V. Friesen, and published in 1978. Ekman, Friesen, and Joseph C. Hager published a significant update to FACS in 2002. Movements of individual facial muscles are encoded by the FACS from slight different instant changes in facial appearance. It is a common standard to systematically categorize the physical expression of emotions, and it has proven useful to psychologists and to animators. Due to subjectivity and time consumption issues, the FACS has been established as a computed automated system that detects faces in videos, extracts the geometrical features of the faces, and then produces temporal profiles of each facial movement. Uses Using the 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. As AUs are independent of any interpretation, they can be used for any higher order decision making process including recognition of basic emotions, or pre-programmed commands for an ambient intelligent environment. The FACS manual is over 500 pages in length and provides the AUs, as well as Ekman's interpretation of their meanings. The FACS defines AUs, as contractions or relaxations of one or more muscles. It also defines a number of "action descriptors", which differ from AUs in that the authors of the 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, the 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. Although the labeling of expressions currently requires trained experts, researchers have had some success in using computers to automatically identify the FACS codes. Computer graphical face models, such as Artnatomy, allow expressions to be artificially posed by setting the desired action units. The use of the FACS has been proposed for use in the analysis of depression, and the measurement of pain in patients unable to express themselves verbally. The FACS is designed to be self-instructional. People can learn the technique