“…An XGBoost classifier, Feat-XGB [67], was used as the AU detector, which used PCA-reduced HOG features for AU predictions, as with OpenFace [54]. It was trained for 20 AUs (1, 2, 4, 5, 6, 7, 9, 10, 12, 14, 15, 17, 18, 20, 23, 24, 25, 26, 28, 43) using BP4D [57], BP4D+ [68], DISFA [55], DISFA+ [69], CK+ [70], JAFFE [71], Shoulder Pain [58], and EmotioNet [72] and validated using WIDER FACE [51], 300W [73], NAMBA [24], and BIWI-Kinect [74]. The average F1 score was 0.54 (AU4 = 0.64 and AU12 = 0.83) [42].…”