Skewness measures the symmetry of the variation of a surface about its mean plane. A Gaussian surface, having a symmetrical shape for the height distribution, has a skewness of zero. A plateau honed surface with predominant plateau and deep valleys will tend to have a negative skew, whereas a surface comprised of disproportionate number of peaks will have positive skew. The digital representation of this parameter is displayed below.
where M is the number of columns in the surface and N is the number of rows in the surface.