Table 2.

Facial features introduced by Parra et al. in [16].

No.	Element	Formula	Description
f0	Eyebrows	$|\angle (P0,P9\left)\right|$	Y-axis position of the left and right sides.
f1	Eyebrows	$|\angle (P2,P7\left)\right|$	Y-axis position of the left and right sides.
f2	Eyebrows	$|\angle (P4,P5\left)\right|$	Y-axis position of the left and right sides.
f3	Eyebrows	$max(L/M,M/L)$	Eyebrows’ height points ratio.
f4	Eyebrows	$m(P0,P9)$	Y-axis position of the eyebrows.
f5	Eyebrows	$m(P2,P7)$	Y-axis position of the eyebrows.
f6	Eyebrows	$m(P4,P5)$	Y-axis position of the eyebrows.
f7	Eyes	$|\angle (P10,P19\left)\right|$	Y-axis position of the eyes’ corner.
f8	Eyes	$max(B_l/B_r,B_r/B_l)$	Eyes’ width ratio.
f9	Eyes	$max(D/E,E/D)$	Eye to head side distance ratio.
f10	Eyes	$max(H/I,I/H)$	Eye to nose distance ratio.
f11	Eyes	$max(N/O,O/N)$	Eyes’ average opening ratio.
f12	Eyes	$max(N_l/O_r,O_r/N_l)$	Eyes’ outer opening ratio.
f13	Eyes	$max(N_r/O_l,O_l/N_r)$	Eyes’ inner opening ratio.
f14	Mouth	$|\angle (P28,P34\left)\right|$	Y-axis position of the corners.
f15	Mouth	$max(F/G,G/F)$	Eye to mouth distance ratio.
f16	Mouth	$max(P_l/Q_l,Q_l/P_l)$	Mouth’s outer opening ratio.
f17	Mouth	$max(P_u/Q_u,Q_u/P_u)$	Mouth’s inner opening ratio.
f18	Mouth	$max(V_l/A,V_r/A)$	Mouth’s half width and head width ratio.
f19	Mouth	$max(P_l/W,Q_l/W)$	Mouth’s outer height and its width ratio.
f20	Mouth	$max(P_u/W,Q_u/W)$	Mouth’s inner height and its width ratio.
f21	Mouth	$max(W_l/W,W_r/W)$	Mouth’s half perimeter and its width ratio.
f22	Nose	$|\angle (P23,P27\left)\right|$	Y-axis position of the nose.
f23	Combined	$|\angle (P22,P37\left)\right|$	Y-axis position of the nose and mouth.
f24	Combined	$max(J/K,K/J)$	Nose-to-mouth distance ratio.
f25	Combined	$max(T/A,U/A)$	Eyebrows-to-mouth distance and the head’s width ratio.
f26	Combined	$max(R/A,S/A)$	Eyebrows-to-mouth distance and the head’s width ratio.
f27	Combined	$C/A$	Mouth-to-chin distance and the head’s width ratio.
f28	Combined	$X/A$	Nose-to-mouth distance and the head’s width ratio.

In f3, L and M are the average heights of all the points in the left and right eyebrows, respectively. In f11, $N=(N_l+N_r)/2$, similarly, $O=(O_l+O_r)/2$. In f19, f20 and f21, W is the distance depicted in Figure 3d, with the perimeter values $W_l$ and $W_r$ calculated as $W_l=\overline{\mathrm{S}}(P28,P29,P30,P31,P37,P38,P39)$ and $W_r=\overline{\mathrm{S}}(P31,P32,P33,P34,P35,P36,P37)$.