Integrate MSE and color density better for low qualities
Integrate MSE and color density better for low qualities

Separate condition for color density ratio makes quality configuration via error-threshold argument harder
rflynn/imgmin,rflynn/imgmin,jibsen/imgmin,micmro/imgmin,pornel/imgmin,pornel/imgmin,jibsen/imgmin,micmro/imgmin,rflynn/imgmin,jibsen/imgmin,jibsen/imgmin,micmro/imgmin,pornel/imgmin,pornel/imgmin,micmro/imgmin,rflynn/imgmin