A method for displaying gray levels in a PDP by generating gray data corresponding to externally input image signals and displaying the gray data on the PDP is disclosed. The method comprises generating reference signals based on the image signals, determining a spread filter value according to states of the reference signals, applying the spread filter value to the gray data and generating final gray data, and displaying the final gray data on the PDP. The present invention reduces contour noise generated between moving pictures' adjacent grays.