1. A method of expressing gray scales of a plasma display panel representing the gray scales using a sum of weights assigned to a plurality of subfields having discharge cells selected to be turned on, the method comprising: (a) extracting a first gray scale arrangement, including a gray scale n using (k−1) of the subfields to a gray scale m using k of the subfields (n<m, n is an integer), from a second gray scale arrangement, including a gray scale 1 to the gray scale m using k of the subfields between a 1st subfield and a jth subfield, when a number of subfields used for representing gray scale (i+1) (1≦i≦(m−1)) is the same or greater than a number of subfields used for representing gray scale i; (b) generating a third gray scale arrangement including a gray scale (n+p) to a gray scale (m+p) by adding a weight p assigned to a (j+1)th subfield to the first gray scale arrangement including the gray scale n to the gray scale m; and (c) generating a fourth gray scale arrangement including the gray scale 1 to the gray scale (m+p) by selecting the second gray scale arrangement in a range from gray scale 1 to a gray 15 scale (n+p−1) and selecting the third gray scale arrangement in a range from the gray scale (n+p) to the gray scale (m+p).