1. An image processing method, for rendering a three-dimensional (3D) effect by transforming a first quadrilateral image to a second quadrilateral image and displaying the same on a monitor, 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; scaling image data of the first blocks to respectively generate image data of the second blocks to obtain the second quadrilateral image; and displaying the second quadrilateral image on the monitor, wherein the first blocks comprise a first corresponding block and a second corresponding block, the first corresponding block comprises a first predetermined number of scan lines, and the second corresponding block comprises a second predetermined number of scan lines, wherein in accordance with an inverse non-linear relationship, the first predetermined number of scan lines is larger than the second predetermined number of scan lines when the block, within the second blocks, corresponding to the first corresponding block is narrower or smaller than the block, within the second blocks, corresponding to the second corresponding block.