1. An image processing method, for rendering a three-dimensional (3D) effect by transforming a first quadrilateral image to a second quadrilateral image, the method comprising: providing the first quadrilateral image; generating an outline associated with the second quadrilateral image according to the first quadrilateral image and the 3D effect; dividing an area within the outline into a plurality of second blocks, and correspondingly determining a plurality of first blocks from the first quadrilateral image; and scaling image data of the first blocks to respectively generate image data of the second blocks to obtain the second quadrilateral image.