1. A multi-gray-scale image display method for displaying a multi-gray-scale image on a plasma display panel (PDP) by diffusing, as an error, a part of gray scale data of an input image requiring more than a predetermined gray scale resolution of the PDP to a target pixel from different adjacent pixels in a scanning direction according to a diffusion factor corresponding to each pixel, the method comprising: (a) determining if the target pixel to which the error is diffused from the adjacent pixels is positioned in a predetermined upper line of the input image; and (b) setting the diffusion factor that determines the error diffused from an adjacent pixel differently when the target pixel to which the error is diffused from the adjacent pixel is positioned in the predetermined upper line of the input image.