Thesis (PDF) - Signal & Image Processing Lab

6.2. MORPHOLOGICAL OPERATIONS ON THE EXTREMA-WATERSHED TREE 81
The result of the erosion and the opening operations on the image Lena are shown
in Figs. 6.4 and 6.5, respectively. As one can see, these operators create no significant
artifacts (unlike the the trenches that are added by boundary topographic operators,
as shown in Chapter 4). Very small components were removed, whereas the larger
ones were preserved (by opening) or shrank (by erosion). Moreover, the average gray
level of the picture did not change; in particular, the picture did not become darker,
which is what usually happens after a standard erosion or opening. In addition,
in Fig. 6.7 the filtering effect on a corrupted Lena image is shown. The image is
corrupted with salt and pepper noise constituting of random black and white pixels.
It is seen that after the filtering there is no sign of noise, and the resulted image is
very similar to a filtered image without the noise. A comparison between the two
results (filtered with and without the noise) is shown in Fig. 6.8. The image shown is
the gray level difference between the filtered original and filtered noisy images, both
obtained by opening and erosion. An additional example is shown in Figs. 6.11 and
6.10, with respect to the synthetic image “Simba”. The Fig. 6.12 results of filtering
a binary image, first introduced in Fig. 1.1, are presented. All the noise, except for
noise on the edges, has been removed.