1. A method of displaying a 3-dimensional image, comprising: forming a first parallax image for a left eye and a second parallax image for a right eye, each of the first and second parallax images including a plurality of display images, said display images corresponding to projections of virtual images of an object at different depths as viewed by the respective eye; controlling a brightness level of each of the display images in each of the first and second parallax images; and displaying the first and second parallax images.