Recently some modified GVF active contour model have been
developed to address this issue. Li et al. [30] proposed edge
preserving gradient vector flow (EPGVF), which makes V(x, y)
projection along object edges to be better for preserving edges.
Some improved results have been acquired by a robust region-
based segmentation method introduced by Xie and Mirmehdi
[12]. By generalizing the Laplacian operator fromflat space toman-
ifold during diffusion, Lu et al. [21] presented gradient vector flow
over manifold (GVFOM) which outperforms GVF in terms of weak
edge preserving, concavities convergence. Tang [16] exploited the
multi-direction GVF active contour to trace the boundary of the
skin cancer even if there are other objects near the skin cancer re-
gion. By integrating the gradient vector flow and the prior direc-
tional information, Zhu et al. [31] introduced gradient and
direction vector flow, which is capable of addressing the issue of
weak edge leakage in some cases. Kovacs et al. [32] proposed harris
function based active contour external force for detecting complex
boundaries with weak contrast and high curvatures.