“…It maps the distance metric space into a new metric space (Kulis, 2012 ). The commonly used basic distance metrics in kinship verification are Euclidean distance (Yan et al, 2014b ), Mahalanobis distance (Hu et al, 2014 , 2017 ; Kou et al, 2015 ; Lu et al, 2014c ; Wei et al, 2019 ; Yan et al, 2014a ; Zhang et al, 2015 ), bilinear similarity (Fang et al, 2016 ; Qin et al, 2016 ; Xu and Shang, 2016a , b ; Zhou et al, 2016a , b ), graph learning (Guo et al, 2014 ; Liang et al, 2018 ), cosine similarity (Yan et al, 2015 ; Yan, 2017 ), CCA (Lei et al, 2017 ) and other metric patterns (Liu et al, 2017 ; Liu and Zhu, 2017 ; Wu et al, 2018 ; Zhang et al, 2016 ; Zhao et al, 2018 ). Selective methods are illustrated in Fig.…”