The PVD technique proposed by Chang & Tseng (2012) exploits the correlation of a target pixel with its neighboring pixels. Although they addressed the fall off boundary problem, but another problem, known as fall in error problem has occurred, which was explained in (Swain & Lenka, 2013). This section describes all the seven variants of PVD based on correlation of target pixel with neighboring pixels (Swain & Lenka, 2013; Swain & Lenka, 2015).