An image of each field displayed on a plasma display panel corresponding to input image signals is divided into sub-fields of different weights, the sub-fields being divided into two continuous sub-field groups having a different weighting value, and in which the weighting values of the sub-fields combine to display grays. The method includes generating original grays; determining a diffusion filter value; generating final grays by applying the diffusion filter value to the original grays; generating gray data corresponding to the final grays, the gray data being distributed over the two sub-field groups; and displaying an image on the PDP according to the gray data. The disclosed method and system reduce flicker and contour noise and other display problems associated with the display of 50 Hz Phase Alternating by Line image signals.