Facial Action Coding System
Facial Action Coding System (FACS) is a system originally developed by Paul Ekman and Wallace Friesen in 1976, to taxonomize every conceivable human facial expression. It is the most popular standard currently used to systematically categorize the physical expression of emotions, and it has proven useful both to psychologists and to animators.
It defines expressions as one of 46 "Action Units", which is a contraction or relaxation of one or more muscles. For example, it can be used to distinguish the two types of smiles as follows:
- insincere and voluntary Pan American smile: contraction of zygomatic major alone
- sincere and involuntary Duchenne smile: contraction of zygomaticus major and inferior part of orbicularis oculi, and pars orbitalis
Although the labeling of expressions currently requires trained experts, researchers have had some success in using computers to automatically identify FACS codes, and thus quickly identify emotions. [1]
Codes for common action units
- 1 Inner Brow Raiser -- Frontalis, pars medialis
- 2 Outer Brow Raiser -- Frontalis, pars lateralis
- 4 Brow Lowerer -- Corrugator supercilii, Depressor supercilii
- 5 Upper Lid Raiser -- Levator palpebrae superioris
- 6 Cheek Raiser -- Orbicularis oculi, pars orbitalis
- 7 Lid Tightener -- Orbicularis oculi, pars palpebralis
- 9 Nose Wrinkler -- Levator labii superioris alaquae nasi
- 10 Upper Lip Raiser -- Levator labii superioris
- 11 Nasolabial Deepener -- Zygomaticus minor
- 12 Lip Corner Puller -- Zygomaticus major
- 13 Cheek Puffer -- Levator anguli oris (a.k.a. Caninus)
- 14 Dimpler -- Buccinator
- 15 Lip Corner Depressor -- Depressor anguli oris (a.k.a. Triangularis)
- 16 Lower Lip Depressor -- Depressor labii inferioris
- 17 Chin Raiser -- Mentalis
- 18 Lip Puckerer -- Incisivii labii superioris and Incisivii labii inferioris
- 20 Lip stretcher -- Risorius w/ platysma
- 22 Lip Funneler -- Orbicularis oris
- 23 Lip Tightener -- Orbicularis oris
- 24 Lip Pressor -- Orbicularis oris
- 25 Lips part -- Depressor labii inferioris or relaxation of Mentalis, or Orbicularis oris
- 26 Jaw Drop -- Masseter, relaxed Temporalis and internal Pterygoid
- 27 Mouth Stretch -- Pterygoids, Digastric
- 28 Lip Suck -- Orbicularis oris
- 41 Lid droop -- Relaxation of Levator palpebrae superioris
- 42 Slit -- Orbicularis oculi
- 43 Eyes Closed -- Relaxation of Levator palpebrae superioris; Orbicularis oculi, pars palpebralis
- 44 Squint -- Orbicularis oculi, pars palpebralis
- 45 Blink -- Relaxation of Levator palpebrae superioris; Orbicularis oculi, pars palpebralis
- 46 Wink -- Relaxation of Levator palpebrae superioris; Orbicularis oculi, pars palpebralis
- 51 Head turn left
- 52 Head turn right
- 53 Head up
- 54 Head down
- 55 Head tilt left
- 56 Head tilt right
- 57 Head forward
- 58 Head back
- 61 Eyes turn left
- 62 Eyes turn right
- 63 Eyes up
- 64 Eyes down