mandel[c_] := Module[{n, v, z, a}, 
   z = N[c]; n = 0; a = N[1 + Sqrt[1 + Abs[c]]]; 
    While[n < n0 && Abs[z] < a, n++; z = z*z + c]; 
    Return[If[n < n0, n, Infinity]]]
 
n0 = 100
 
height[x_, y_] := 1/(1 + mandel[x + y*I])
