These figures are similar to those presented here, except that the top "sector" in this figure has a different junction geometry ("junctions" refers to the intersection of the contours in the images). These figures are stereopairs, and should be fused by either crossing or diverging your eyes. When the two grey diamonds appear in front of the background (left two stereopairs if cross fused), the odd sectors appear opaque, whereas the other three sectors appear transparent. This causes a large difference in the apparent lightness of these sectors: the odd sector in the top figure appears to contain a dark "coating" that is attributed to the background in the other sectors. Similarly, the odd sector in the bottom figure appears to contain a light "coating" that is attributed to the background in the other three sectors. The point of these figures is to demonstrate the critical importance of the junction geometry in generating lightness illusions and illusory contours.