Data undersampling (RD)
| AU1 + 2 | AU43_5 | UpperNone | Undersampled per class | Total balanced training set | |
|---|---|---|---|---|---|
| Upper face | |||||
| frames, n | 1213 | ∼19,500 | ∼150,000 | 1213 | 3639 |
| AU25 + 26 + 16 | AU25 + 26 + 18i | AU25 + 26 | Undersampled per class | Total balanced training set | |
| Lower face | |||||
| frames, n | 310 | ∼15,000 | ∼15,000 | 310 | 930 |
In the upper face, the smallest category was AU1 + 2 with only 1213 frames (in total, from all RD subjects). On the contrary, AU43_5 category had ∼19,500 frames (after eliminating RD AU45 frames because of time synchronization errors), and UpperNone class included >150,000 images. Consequently, balanced training sets were generated with each including all of the AU1 + 2 frames, and randomly selected 1213 frames from AU43_5 along with 1213 randomly selected UpperNone frames. Therefore, the upper face balanced training sets were each composed of 3639 frames. The same was done for the lower face, where the smallest category was AU25 + 26 + 16 with only 310 frames. Categories AU25 + 26 + 18i and AU25 + 26 contained >15,000 images each. Accordingly, each lower face balanced training set included 930 frames.