改善了劉海部分的不自然結果
Exclude the between-eyes part from the skin recoloring in Warper.cpp
Modify the Blend() in FaceDresser.cpp
improve the recolor in Warper.cpp (detect skin pixels in between-eyes area and then include these skin pixels into the recoloring process)
add four member variables in Warper.h (skin_mean, skin_cov, model_skin_mean, model_skin_cov). these variables are instantiated in BuildSkinModel() function
relayout the output windows