1. A multilevel texture processing method for mapping an image onto a 3D model with a texture mapping, the method comprising the steps of: providing the image to the 3D model; converting the image and the texture mapping to a same spatial coordinate system and dividing them into a plurality of polygons; comparing the image with the texture mapping within the spatial coordinate system to extract overlapped polygons; using the pixel intensity of the overlapped polygons to compute a statistics mean for adjusting the pixel intensity of the image accordingly; using a prescribed condition to select the texture of one of the image and the texture mapping as the texture of the polygon; smoothing the texture of the polygon; making the pixels inside the polygon continuous; and restoring the polygon and storing the 3D model in memory.