i usually just export the chanel as bmp(bw/greys, in Adobe or Gimp), force the material to have opacity slot.
In 3d preview window activate smooth textured.
menu at the right :
material...maps...diffuse...one difusse bitmap, and one opacity.
In 3d preview window activate smooth textured.
menu at the right :
material...maps...diffuse...one difusse bitmap, and one opacity.