I am seeing references to FACS on your website. What exactly is that?


Can you give me some details on what FACS and AU are in terms of your technology?

Detect emotion using just mouth and jaw - Unity SDK

Facial Action Coding System (FACS) is a well-known approach for describing and annotating facial expressions using using single or combinations of facial muscle movements.

FACS describes all of expressions in term of Action Units (AUs).

Check out this page for more details.


Okay, that sounds interesting. Can you clarify the theoretical connection between FACS and Affectiva?


Affectiva uses the Action Units (AUs) in the Facial Action Coding System as a taxonomy for building its classifiers to detect changes facial expressions. These facial expressions are then mapped to higher level emotions (sadness, fear, anger, joy, etc.).


Is the link between the AU codes and the Affectiva Facial Expressions documented?

Some seem obvious (e.g. the Affectiva “Chin Raise” is presumably AU17 “Chin Raise”), but others aren’t so obvious…

Some of the things I’d like to know are:

  • is the Affectiva Facial Expression “Brow Furrow” the same as AU4 “Brow Lowerer”
  • is there an Affectiva equivalent for AU10 “Upper Lip Raiser”?


Yes! most of the expression classifiers follow the definitions in FACS … We tried to use friendlier names for the non techies

For more information about which classifiers translate to which AUs, please refer to our published paper in CHI’16



Thank you for the information.
After I read your publications, I found that smile indicates AU 12 and smirk means asymmetric smile(asymmetric AU12/AU14).
Still, it is difficult to find the information about how the two smirks which Affdex SDK’ result shows could be distinguished.

The AU indexes which Affdex SDK provides are as follows in order.

(1). smile 2. innerBrowRaise 3. browRaise 4. browFurrow 5. noseWrinkle 6.upperLipRaise
7. lipCornerDepressor 8. chinRaise 9. lipPucker 10 .lipPress 11. lipSuck 12. mouthOpen 13.smirk
14. eyeClosure 15. attention 16. eyeWiden 17. cheekRaise 18. lidTighten 19. dimpler 20. lipStretch
21. jawDrop 22. relaxed 23. smiley 24. laughing 25. kissing 26. disappointed 27. rage 28. smirk
29. wink 30.stuckOutTongueWin 31. stuckOutTongue 32. flushed 33. scream

I hope you can help me here. I would like to match AU with the first smirk (number 13) and, also, the second smirk (number 28).
Furthermore, if it is possible, I would like to know original AU terms for the classifiers which were turned into friendlier names such as attention, relaxed, smiley, laughing, kissing, disappointed, and rage.

Thank you.


The SDK includes three classes of metrics expressions, emotions and emojis. The AUs are expressions.

More information about the different metrics available in each class is here: