41 lines
2.2 KiB
Markdown
41 lines
2.2 KiB
Markdown
---
|
|
id: action-units
|
|
title: Action units
|
|
---
|
|
|
|
Action units (AUs) are individual facial musculature arrangements specified in the [Facial Action Coding System (FACS)](https://en.wikipedia.org/wiki/Facial_Action_Coding_System), combinations of which can account for all possible facial expressions[^1]. OpenDBM outputs framewise values for AU presence and intensity for the following AUs:
|
|
|
|
| Action unit number | Description |
|
|
| ----------- | ----------- |
|
|
| AU1 | Inner brow raiser |
|
|
| AU2 | Outer brow raiser |
|
|
| AU4 | Brow lowerer |
|
|
| AU5 | Upper lid raiser |
|
|
| AU6 | Cheek raiser |
|
|
| AU7 | Lid tightener |
|
|
| AU9 | Nose wrinkler |
|
|
| AU12 | Lip corner puller |
|
|
| AU15 | Lip corner depressor |
|
|
| AU16 | Lower lip depressor |
|
|
| AU20 | Lip stretcher |
|
|
| AU23 | Lip tightener |
|
|
| AU26 | Jaw drop |
|
|
|
|
For each of the AUs in the table above, the following raw variables are calculated:
|
|
|
|
## Raw Variables
|
|
|
|
| Variable | Description |
|
|
| ----------- | ----------- |
|
|
| `fac_auXXpres` | **Action Unit presence,** where XX refers to the action unit. This is a binary (1/0) variable, where 1 signifies presence of the action unit and 0 signifies its absence as determined by OpenFace. |
|
|
| `fac_auXXint` | **Action Unit intensity,** where XX refers to the action unit. This is a continuous (0-5) variable, where 0 signifies no presence and 5 signifies maximum presence, as determined by OpenFace. |
|
|
## Derived Variables
|
|
|
|
| Variable | Description |
|
|
| ----------- | ----------- |
|
|
| `fac_auXXpres_pct` | **Action Unit presence percentage.** Using the binary vector fac_auXXpres, the percentage of video frames where an AU was present is calculated into this variable. |
|
|
| `fac_auXXint_mean` | **Action Unit intensity mean.** Mean value of fac_auXXint over the course of the video. |
|
|
| `fac_auXXint_std` | **Action Unit intensity standard deviation.** Standard deviation of fac_auXXint over the course of the video. |
|
|
|
|
|
|
[^1]: Ekman, R. (1997). What the face reveals: Basic and applied studies of spontaneous expression using the Facial Action Coding System (FACS). Oxford University Press, USA. |