1. A method for rendering image signals in an apparatus for rendering an image signal comprising pixels which are composed of three different sub-pixels among four or more different sub-pixels representing four or more color signals respectively, the method comprising: (a) selecting three-color signals out of the four or more color signals to be outputted according to a type of sub-pixel, which forms a predetermined pixel; (b) obtaining values of the selected three-color signals in peripheral pixels of the pixels; (c) calculating brightness values of each sub-pixel of the pixel by using the values of the selected three-color signals and corresponding color signal values of the peripheral pixels; and (d) driving a display, which controls brightness of an image that is represented in the display according to the calculated brightness values of sub-pixels.