3 Increase selection's Feather to 150 (Selections>Modify>Feather). The feather size depends on the actual size of your image.
4 Invert selection by pressing CTRL+Shift+I. Then, Floodfill your selection with solid black color. Repeat this procedure 3-4 times until you attain the desired darkness.
your selection with solid black color. Repeat this procedure 3-4 times until you attain the desired darkness.
