I just double checked the image to make sure the center black area was fixed. Doubling the max iteration count from 100000 to 200000 had no effect on the image (other than making it take longer to draw). You do have to increase the max iteration count from Jim's original 1000 to 100000 to get the center area to stop shrinking. The image I posted was anti-aliased (the equivalent of drawing it at 6000 x 4500 and then downsampling to 1200 x 900) to make the detail along the edge of the black area easier to see.