“…Another drawback of almost all the datasets is the data imbalance issue: the distribution between easy frontal faces and more challenging orientations is heavily unbalanced. Techniques to increase the number of hard faces [195] or to enhance the contribution of hard examples (such as HEM [150]) can be used to alter the data distribution space and [82] Model based DCNN 3 300W-LP, AFLW2000, BIWI, CAS-PEAL, DriveFace 2019 Yang et al [88] DCNN 3 300W-LP, AFLW2000, BIWI 2020 Barra et al [130] Model based 3 AFLW, BIWI, Pointing'04 2020 Cao et al [76] DCNN 3 300W-LP, AFLW2000, BIWI 2020 Dai et al [90] DCNN 3 300W-LP, AFLW2000, BIWI 2020 Dapongy et al [83] Model based 3 300W, 300W-LP, AFLW2000, CelebA, WFLW 2020 Ewaisha et al [168] Multi-task DCNN 3 CAVE 2020 Valle et al [98] Multi-task DCNN 3 300W-LP a,c , AFLW a,c , AFLW2000 a , BIWI a , COFW c , WFLW a,c 2020 Wang et al [182] PnP Model based 3 300W, AFLW2000 2020 Zhang et al [183] DCNN 3 300W-LP, AFLW2000, BIWI 2020 Zhang et al [167] Multi-task DCNN 3 AFLW a,b,c 2020 Zhou et al [7] DCNN 3 300W-LP, AFLW2000, BIWI, CMU Panoptic 2021 Albiero et al [166] Multi-task DCNN 3 300W-LP a , AFLW2000 a , BIWI a , WIDER Multi-task DCNN + ASM 3 300W a,b , WFLW a,b 2021 Hu et al [185] DCNN 3 300W-LP, AFLW2000, BIWI 2021 Khan et al [80] Segmentation based Soft-max classifier 3 AFLW, BU, ICT-3DHP, Pointing'04 2021 Liu et al [85] Multi-task DCNN 3 AFLW c , AFLW2000 a , WIDER * 2021 Naina Dhingra [186] DCNN 3 300W-LP, AFLW2000, BIWI 2021 Ruan et al [87] Model based 3DMM + DCNN 3 300W-LP a,c,g , AFLW2000 ⋄• * , Florence g 2021 Sheka et al [91] DCNN 3 300W-LP, AFLW, AFLW2000, BIWI 2021 Viet et al [102] Multi-task DCNN 3 300W-LP a,b , BIWI a,b , CMU Panoptic a,b 2021 Viet et al [69] DCNN 3 300W-LP, AFLW2000, CMU Panoptic, UET-Headpose 2021 Xia et al [99] Multi-task DCNN 3 300W-LP a , 300VW c , WFLW c , WIDER b 2021 Xin et al [187] Model based Graph CNN 3 300W-LP, AFLW2000, BIWI 2021 Wu et al [86] Model based 3DMM + DCNN 3 300W-LP a,c,g , 300VW g , AFLW c , AFLW2000 a,c , Florence g 2022 Cantarini et al [188] Model based D...…”