Another method used to increase the number of apparent intensities on a bit-mapped display is dithering. In an ordered dither, the decision to turn a pixel on or off at point (x,y) depends on the desired intensity l(x,y) at that point and on an n x n dither matrix D(n). The dither matrix is indexed from 0 to (n - 1) along its rows and columns. Each of the integers 0 to n^2 - 1 appears once in the matrix. For instance, when n = 4 we have D(4) =
0 8 2 10
12 4 14 6
3 11 1 9
15 7 13 5
To process the point at x,y), we first compute
Then if l(x,y) > D(i,j)^4 the point (x,y) is turned on; otherwise it is not.