There some bright white or black parts on the edges of result face for seamlessClone

Question

I meet some problem about the function seamlessClone of opencv:

Without other op , simply using seamlessClone op for blending two face image like cv2.seamlessClone(src_img, dst_img, src_mask, center, cv2.NORMAL_CLONE), I test 3 cases:

1) When I use all white mask for src_mask, there will be some white bright parts on the some edges of result face. 2) When I use the same-sized face white mask of src_img for src_mask, there will be some bigger white bright parts on the some edges of result face. 3) When I use the eroded face white mask of src_img for src_mask, there will be some black parts on the some edges of result face.

I can not find the causes and can not fix it. Can anyone give some advises?

Thanks. Looking forward to the reply.