1. A method of performing a lens effect to determine a realistic pixel content of a realistic pixel transformed by a virtual lens having a plurality of points from a plurality of image pixels, the realistic pixel corresponding to a pixel point of the points of the virtual lens, comprising the steps of: providing an offset mask having an offset value corresponding to the pixel point; providing a plurality of weight masks corresponding to the image pixels, respectively, each of the weight masks having a weight value corresponding to the pixel point; calculating a reference pixel position by adding a realistic pixel position of the realistic pixel with the offset value corresponding to the pixel point in the offset mask; selecting one of the image pixels with a position equal to the reference pixel position as a reference pixel; and performing a weighted process on the addition of an adjacent pixel content of an adjacent pixel adjacent to the reference pixel and a reference pixel content of the reference pixel according to the weight value corresponding to the pixel point in a first weight mask of the weight masks, thereby acquiring the realistic pixel content of the realistic pixel.