1. A method of generating a new terrain image, the method comprising: generating an original terrain image through a patch-based synthesis from one or more virtual noise-based terrain models and one or more realistic terrain models; and blending a boundary of the original terrain image to expand the boundary of the original terrain image, wherein blending comprises: selecting a patch size from the original terrain image; selecting a patch area from the original terrain image which is calculated to have a minimum matching error between a regularly overlapped boundary area of the original terrain image and that of the selected patch area; and adding the selected patch area onto the boundary of the original terrain image to complete the new terrain image.