FIG. 7 is an explanatory views showing image examples displayed on the transparent screen and FIG. 7 (a) shows an image of a rear plane in the transparent screen, FIG. 7 (b) shows an image of the rear plane in the transparent screen, the image including a shadow, and FIG. 7 (c) shows an image shown in FIG. 7 (b) after a binarization process is done, and