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, the method comprising: extracting a first gray scale arrangement, including a gray scale n using (k−i) 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; 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; 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 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); and selecting a discharge cell to be turned on and sustain discharging the turned on cell to display the gray scale 1 to the gray scale (m+p) using the fourth gray scale arrangement, wherein the number of subfields used to represent a first gray scale between the gray scale 1 and the gray scale (m+p) is always equal to or less than the number of subfields used to represent a second gray scale, the second gray scale equaling the first gray scale plus one.