In the discussion of the median filter in Ch. 6 (Sec. 6.4.2), we noticed that this type of filter can somehow alter two-dimensional image structures. Figure 10.1 illustrates once more how corners are rounded off, holes of a certain size are filled, and small structures, such as single dots or thin lines, are removed. The median filter thus responds selectively to the local shape of image structures, a property that might be useful for other purposes if it can be applied not just randomly but in a controlled fashion. Altering the local structure in a predictable way is exactly what “morphological” filters can do, which we focus on in this chapter.
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