1. A method of generating a three-dimensional (3D) image using a first two-dimensional (2D) image and a second 2D image, the method comprising: upscaling the first 2D image and the second 2D image; and performing, simultaneously, a cross filtering to sharpen the second 2D image using the first 2D image and a cross filtering to sharpen the first 2D image using the second 2D image.