However, we cannot find any structuring element which allows us to detect the small cells and remove the large ones. Every structuring element that is small enough to allow the dark cells remain in the image would not remove the large cells, either. This is illustrated in which is the result of applying a 7 pixel wide circular structuring element to the thresholded image. It is common for opening to be used in conjunction with closing to achieve more subtle effects, as described in the section on closing . Interactive Experimentation You can interactively experiment with this operator by clicking here .
Exercises Apply opening to using square structuring elements of increasing size.
Compare the results obtained with the different sizes. If your implementation of the operator does not support graylevel opening, threshold the input image. Now describe two 2-D shapes that opening couldn't distinguish between. References R. Haralick and L. Shapiro Computer and Robot Vision , Vol. Local Information Specific information about this operator may be found here.