METHOD OF SMOOTHING IMAGE DATA

Original image data items a.sub.1, a.sub.2, . . . a.sub.N with respect to a horizontal or vertical row of pixels in a two-dimensional image are obtained and then smoothed by converting a.sub.n to a'.sub.n which is the median value of a.sub.n (a'.sub.n-1 +.alpha.), and (a'.sub.n-1 -.alpha.) (where a'.sub.n-1 is a converted data item which is produced by converting the original image data item a.sub.n-1 to a median value, and .alpha. is a constant), converting a.sub.n to a".sub.n which is the median value of a.sub.n, a".sub.n+1 +.alpha.), and (a".sub.n+1 -.alpha.) (where a".sub.n+1 is a converted data item which is produced by converting the original image data item a.sub.n+1 to a median value), and determining the means value A.sub.n of the converted data items a'.sub.n and a".sub.n with respect to the same pixel and employing the determined mean value A.sub.n as smoothed data.