Jump to content

Facial Action Coding System

From Wikipedia, the free encyclopedia
Muscles of head and neck

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.[1] It was later adopted by Paul Ekman and Wallace V. Friesen, and published in 1978.[2] Ekman, Friesen, and Joseph C. Hager published a significant update to FACS in 2002.[3] Movements of individual facial muscles are encoded by the FACS from slight different instant changes in facial appearance. It has proven useful to psychologists and to animators.


Blind athlete expressing joy in athletic competition. The fact that unsighted persons use the same expressions as sighted people shows that expressions are innate.

In 2009, a study was conducted to study spontaneous facial expressions in sighted and blind judo athletes. They discovered that many facial expressions are innate and not visually learned.[4]


Using the FACS[5] 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:[6]

The FACS is designed to be self-instructional. People can learn the technique from a number of sources including manuals and workshops,[7] and obtain certification through testing.[8]

Although the labeling of expressions currently requires trained experts, researchers have had some success in using computers to automatically identify the FACS codes.[9] One obstacle to automatic FACS code recognition is a shortage of manually coded ground truth data.[10]


Use in medicine[edit]

The use of the FACS has been proposed for use in the analysis of depression,[11] and the measurement of pain in patients unable to express themselves verbally.[12]

Cross-species applications[edit]

The original FACS has been modified to analyze facial movements in several non-human primates, namely chimpanzees,[13] rhesus macaques,[14] gibbons and siamangs,[15] and orangutans.[16] More recently, it was developed also for domestic species, including dogs,[17] horses[18] and cats.[19] Similarly to the human FACS, the animal FACS has manuals available online for each species with the respective certification tests.[20]

Thus, the FACS can be used to compare facial repertoires across species due to its anatomical basis. A study conducted by Vick and others (2006) suggests that the FACS can be modified by taking differences in underlying morphology into account. Such considerations enable a comparison of the homologous facial movements present in humans and chimpanzees, to show that the facial expressions of both species result from extremely notable appearance changes. The development of FACS tools for different species allows the objective and anatomical study of facial expressions in communicative and emotional contexts. Furthermore, a cross-species analysis of facial expressions can help to answer interesting questions, such as which emotions are uniquely human.[21]

The Emotional Facial Action Coding System (EMFACS)[22] and the Facial Action Coding System Affect Interpretation Dictionary (FACSAID)[23] consider only emotion-related facial actions. Examples of these are:

Emotion Action units
Happiness 6+12
Sadness 1+4+15
Surprise 1+2+5B+26
Fear 1+2+4+5+7+20+26
Anger 4+5+7+23
Disgust 9+15+17
Contempt R12A+R14A

Computer-generated imagery[edit]

FACS coding is also used extensively in computer animation, with facial expressions being expressed as vector graphics of AUs.[24] FACS vectors are used as weights for blendshapes corresponding to each AU, with the resulting face mesh then being used to render the finished face.[25] Deep learning techniques can be used to determine the FACS vectors from face images obtained during motion capture acting or other performances.[26]

Codes for action units[edit]

For clarification, the FACS is an index of facial expressions, but does not actually provide any bio-mechanical information about the degree of muscle activation. Though muscle activation is not part of the FACS, the main muscles involved in the facial expression have been added here.

Action units (AUs) are the fundamental actions of individual muscles or groups of muscles.

Action descriptors (ADs) are unitary movements that may involve the actions of several muscle groups (e.g., a forward‐thrusting movement of the jaw). The muscular basis for these actions has not been specified and specific behaviors have not been distinguished as precisely as for the AUs.

For the most accurate annotation, the FACS suggests agreement from at least two independent certified FACS encoders.

Intensity scoring[edit]

Intensities of the FACS are annotated by appending letters A–E (for minimal-maximal intensity) to the action unit number (e.g. AU 1A is the weakest trace of AU 1 and AU 1E is the maximum intensity possible for the individual person).

  • A Trace
  • B Slight
  • C Marked or pronounced
  • D Severe or extreme
  • E Maximum

Other letter modifiers[edit]

There are other modifiers present in FACS codes for emotional expressions, such as "R" which represents an action that occurs on the right side of the face and "L" for actions which occur on the left. An action which is unilateral (occurs on only one side of the face) but has no specific side is indicated with a "U" and an action which is bilateral but has a stronger side is indicated with an "A" for asymmetric.

List of AUs and ADs (with underlying facial muscles)[edit]

Main codes[edit]

AU number FACS name Muscular basis
0 Neutral face
1 Inner brow raiser frontalis (pars medialis)
2 Outer brow raiser frontalis (pars lateralis)
4 Brow lowerer depressor glabellae, depressor supercilii, corrugator supercilii
5 Upper lid raiser levator palpebrae superioris, superior tarsal muscle
6 Cheek raiser orbicularis oculi (pars orbitalis)
7 Lid tightener orbicularis oculi (pars palpebralis)
8 Lips toward each other orbicularis oris
9 Nose wrinkler levator labii superioris alaeque nasi
10 Upper lip raiser levator labii superioris, caput infraorbitalis
11 Nasolabial deepener zygomaticus minor
12 Lip corner puller zygomaticus major
13 Sharp lip puller levator anguli oris (also known as caninus)
14 Dimpler buccinator
15 Lip corner depressor depressor anguli oris (also known as triangularis)
16 Lower lip depressor depressor labii inferioris
17 Chin raiser mentalis
18 Lip pucker incisivii labii superioris and incisivii labii inferioris
19 Tongue show
20 Lip stretcher risorius with platysma
21 Neck tightener 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

Head movement codes[edit]

AU number FACS name Action
51 Head turn left
52 Head turn right
53 Head up
54 Head down
55 Head tilt left
M55 Head tilt left The onset of the symmetrical 14 is immediately preceded or accompanied by a head tilt to the left.
56 Head tilt right
M56 Head tilt right The onset of the symmetrical 14 is immediately preceded or accompanied by a head tilt to the right.
57 Head forward
M57 Head thrust forward The onset of 17+24 is immediately preceded, accompanied, or followed by a head thrust forward.
58 Head back
M59 Head shake up and down The onset of 17+24 is immediately preceded, accompanied, or followed by an up-down head shake (nod).
M60 Head shake side to side The onset of 17+24 is immediately preceded, accompanied, or followed by a side to side head shake.
M83 Head upward and to the side The onset of the symmetrical 14 is immediately preceded or accompanied by a movement of the head, upward and turned or tilted to either the left or right.

Eye movement codes[edit]

AU number FACS name Action
61 Eyes turn left
M61 Eyes left The onset of the symmetrical 14 is immediately preceded or accompanied by eye movement to the left.
62 Eyes turn right
M62 Eyes right The onset of the symmetrical 14 is immediately preceded or accompanied by eye movement to the right.
63 Eyes up
64 Eyes down
65 Walleye
66 Cross-eye
M68 Upward rolling of eyes The onset of the symmetrical 14 is immediately preceded or accompanied by an upward rolling of the eyes.
69 Eyes positioned to look at other person The 4, 5, or 7, alone or in combination, occurs while the eye position is fixed on the other person in the conversation.
M69 Head or eyes look at other person The onset of the symmetrical 14 or AUs 4, 5, and 7, alone or in combination, is immediately preceded or accompanied by a movement of the eyes or of the head and eyes to look at the other person in the conversation.

Visibility codes[edit]

AU number FACS name
70 Brows and forehead not visible
71 Eyes not visible
72 Lower face not visible
73 Entire face not visible
74 Unscorable

Gross behavior codes[edit]

These codes are reserved for recording information about gross behaviors that may be relevant to the facial actions that are scored.

AU number FACS name Muscular basis
29 Jaw thrust
30 Jaw sideways
31 Jaw clencher masseter
32 [Lip] bite
33 [Cheek] blow
34 [Cheek] puff
35 [Cheek] suck
36 [Tongue] bulge
37 Lip wipe
38 Nostril dilator nasalis (pars alaris)
39 Nostril compressor nasalis (pars transversa) and depressor septi nasi
40 Sniff
41 Lid droop levator palpebrae superioris (relaxation)
42 Slit orbicularis oculi muscle
43 Eyes closed relaxation of levator palpebrae superioris
44 Squint corrugator supercilii and orbicularis oculi muscle
45 Blink relaxation of levator palpebrae superioris; contraction of orbicularis oculi (pars palpebralis)
46 Wink orbicularis oculi
50 Speech
80 Swallow
81 Chewing
82 Shoulder shrug
84 Head shake back and forth
85 Head nod up and down
91 Flash
92 Partial flash
97* Shiver/tremble
98* Fast up-down look

See also[edit]


  1. ^ Hjortsjö CH (1969). Man's face and mimic language. free download: Carl-Herman Hjortsjö, Man's face and mimic language" Archived 2022-08-06 at the Wayback Machine
  2. ^ Ekman P, Friesen W (1978). Facial Action Coding System: A Technique for the Measurement of Facial Movement. Palo Alto: Consulting Psychologists Press.
  3. ^ Ekman P, Friesen WV, Hager JC (2002). Facial Action Coding System: The Manual on CD ROM. Salt Lake City: A Human Face.
  4. ^ Matsumoto, D., & Willingham, B. (2009). "Spontaneous facial expressions of emotion of blind individuals". Journal of Personality and Social Psychology, 96(1), 1-10
  5. ^ Freitas-Magalhães (2012). "Microexpression and macroexpression". In Ramachandran VS (ed.). Encyclopedia of Human Behavior. Vol. 2. Oxford: Elsevier/Academic Press. pp. 173–183. ISBN 978-0-12-375000-6.
  6. ^ Del Giudice M, Colle L (May 2007). "Differences between children and adults in the recognition of enjoyment smiles". Developmental Psychology. 43 (3): 796–803. doi:10.1037/0012-1649.43.3.796. PMID 17484588.
  7. ^ Rosenberg EL. "Example and web site of one teaching professional". Archived from the original on 2009-02-06. Retrieved 2009-02-04.
  8. ^ "Facial Action Coding System". Paul Ekman Group. Retrieved 2019-10-23.
  9. ^ Facial Action Coding System. Retrieved July 21, 2007.
  10. ^ Song, Juan; Liu, Zhilei (10 Mar 2023). "Self-supervised Facial Action Unit Detection with Region and Relation Learning". arXiv:2303.05708 [cs.CV].
  11. ^ Reed LI, Sayette MA, Cohn JF (November 2007). "Impact of depression on response to comedy: a dynamic facial coding analysis". Journal of Abnormal Psychology. 116 (4): 804–9. CiteSeerX doi:10.1037/0021-843X.116.4.804. PMID 18020726.
  12. ^ Lints-Martindale AC, Hadjistavropoulos T, Barber B, Gibson SJ (2007). "A psychophysical investigation of the facial action coding system as an index of pain variability among older adults with and without Alzheimer's disease". Pain Medicine. 8 (8): 678–89. doi:10.1111/j.1526-4637.2007.00358.x. PMID 18028046.
  13. ^ Parr LA, Waller BM, Vick SJ, Bard KA (February 2007). "Classifying chimpanzee facial expressions using muscle action". Emotion. 7 (1): 172–81. doi:10.1037/1528-3542.7.1.172. PMC 2826116. PMID 17352572.
  14. ^ Parr LA, Waller BM, Burrows AM, Gothard KM, Vick SJ (December 2010). "Brief communication: MaqFACS: A muscle-based facial movement coding system for the rhesus macaque". American Journal of Physical Anthropology. 143 (4): 625–30. doi:10.1002/ajpa.21401. PMC 2988871. PMID 20872742.
  15. ^ Waller BM, Lembeck M, Kuchenbuch P, Burrows AM, Liebal K (2012). "GibbonFACS: A Muscle-Based Facial Movement Coding System for Hylobatids". International Journal of Primatology. 33 (4): 809–821. doi:10.1007/s10764-012-9611-6. S2CID 18321096.
  16. ^ Caeiro CC, Waller BM, Zimmermann E, Burrows AM, Davila-Ross M (2012). "OrangFACS: A Muscle-Based Facial Movement Coding System for Orangutans (Pongo spp.)" (PDF). International Journal of Primatology. 34: 115–129. doi:10.1007/s10764-012-9652-x. S2CID 17612028.
  17. ^ Waller BM, Peirce K, Caeiro CC, Scheider L, Burrows AM, McCune S, Kaminski J (2013). "Paedomorphic facial expressions give dogs a selective advantage". PLOS ONE. 8 (12): e82686. Bibcode:2013PLoSO...882686W. doi:10.1371/journal.pone.0082686. PMC 3873274. PMID 24386109.
  18. ^ Wathan J, Burrows AM, Waller BM, McComb K (2015-08-05). "EquiFACS: The Equine Facial Action Coding System". PLOS ONE. 10 (8): e0131738. Bibcode:2015PLoSO..1031738W. doi:10.1371/journal.pone.0131738. PMC 4526551. PMID 26244573.
  19. ^ Caeiro CC, Burrows AM, Waller BM (2017-04-01). "Development and application of CatFACS: Are human cat adopters influenced by cat facial expressions?" (PDF). Applied Animal Behaviour Science. 189: 66–78. doi:10.1016/j.applanim.2017.01.005. ISSN 0168-1591.
  20. ^ "Home". animalfacs.com. Retrieved 2019-10-23.
  21. ^ Vick SJ, Waller BM, Parr LA, Smith Pasqualini MC, Bard KA (March 2007). "A Cross-species Comparison of Facial Morphology and Movement in Humans and Chimpanzees Using the Facial Action Coding System (FACS)". Journal of Nonverbal Behavior. 31 (1): 1–20. doi:10.1007/s10919-006-0017-z. PMC 3008553. PMID 21188285.
  22. ^ Friesen W, Ekman P (1983), EMFACS-7: Emotional Facial Action Coding System. Unpublished manuscript, vol. 2, University of California at San Francisco, p. 1
  23. ^ "Facial Action Coding System Affect Interpretation Dictionary (FACSAID)". Archived from the original on 2011-05-20. Retrieved 2011-02-23.
  24. ^ Walsh, Joseph (2016-12-16). "Rogue One: the CGI resurrection of Peter Cushing is thrilling – but is it right?". The Guardian. ISSN 0261-3077. Retrieved 2023-10-23.
  25. ^ "Discover how to create FACS facial blendshapes in Maya | CG Channel". Retrieved 2023-10-23.
  26. ^ Gudi, Amogh; Tasli, H. Emrah; Den Uyl, Tim M.; Maroulis, Andreas (2015). "Deep learning based FACS Action Unit occurrence and intensity estimation". 2015 11th IEEE International Conference and Workshops on Automatic Face and Gesture Recognition (FG). pp. 1–5. doi:10.1109/FG.2015.7284873. ISBN 978-1-4799-6026-2. S2CID 6283665. Retrieved 2023-10-23.

External links[edit]