viewed as a 3-D surface; that is, its intensity values are in- rest of this figure is explained in the following discussion. s height values over the xy-plane. Then the opening off by b can The gray-scale erosion off by structuring element b, to all locations. The closing, shown in Fig. 9.24(e), is constructed by finding the lowest points reached by any part of the structuring element as it slides against the upper side of the curve. Here, we see that closing suppresses dark details smaller than the structuring element.