I don't think this has anything to do with directed graphs. The operation looks like this. For nonzero c in C, compute the distance d(a(i+1)/c, Z+iZ) to the ne

I don't think this has anything to do with directed graphs. The operation looks like this. For nonzero c in C, compute the distance d(a(i+1)/c, Z+iZ) to the nearest Gaussian integer, where a is an integer. The max distance is A = 1/sqrt(2) so color the point a(1+i)/c proportionally by (A - d(a(i+1)/c, Z+iZ))/A I'm taking a liberty with the description, since computing "the percentage of a(i+1)/c's that are Gaussian integers" is open to interpretation, and if taken literally could mean something else entirely, such as computation of the ratio #(A(c,n)\cap Z+iZ) / n where A(c, n) = { a(i+1)/ c : 1 <= a <= n } which is asking for a proportion products that become Gaussian integers--this is a divisibility test. However, this doesn't show how to vary the brightness of the images.