An image processing apparatus is for rendering a three-dimensional (3D) effect by transforming a first quadrilateral image to a second quadrilateral image. The apparatus includes a target image determining unit, a block determining unit and a graphic unit. The target image determining unit generates an outline associated with the second quadrilateral image according to the first quadrilateral image and the 3D effect. The block determining unit divides an area within the outline into a plurality of second blocks and correspondingly determines a plurality of first blocks from the first quadrilateral image. The graphic unit scales image data of the first blocks to respectively generate image data of the second blocks to obtain the second quadrilateral image.