1. An image display method for a plasma display panel, in which an image of each field displayed on the plasma display panel corresponding to 50 Hz input image signals is divided into a plurality of sub-fields of different weights, the sub-fields again being divided into two continuous sub-field groups and a weighting value of the sub-field groups being different, and in which the weighting values of the sub-fields are combined to display grays, the method comprising: generating original grays based on the input image signals; determining a diffusion filter value based on the input image signals; generating final grays by applying the diffusion filter value to the generated original grays; generating gray data corresponding to the generated final grays, the gray data being distributed over the two sub-field groups; and displaying an image on the plasma display panel according to the generated gray data.