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Chapter 3 ■ Digital Morphology 129

3.4.4 Segmentation of Textures
Closing removes dark detail, and opening joins dark regions. This suggests an
application to textures, and the identification of regions in a image based on
the textural pattern seen there. While this subject will be explored more fully
in Chapter 5, a simple example at this point will probably not detract from
later revelations.
If, for instance, one texture consists of small dark blots and another consists
of larger dark blots then closing by the size of the small blots will effectively
remove them, but will leave some remnant of the larger ones. Now an opening
by the size of the gaps between the large blots will join them into one large dark
area. The boundary between the two regions should now be easy to identify.
An example of this can be seen in Figure 3.31. The original image has two
regions filled with different textures; this image was created by a drawing
package, so the textures repeat exactly, but this is not a requirement. Closing
removes all traces of the smaller texture, and closing creates a solid black
region where the larger texture had appeared. The morphological boundary
extraction procedure can then be applied, giving a solid line along the margin
between the two textures. The line is jagged wherever the boundary cuts a
large blot in two, creating a small one.

(a) (b) (c)

(d) (e)
Figure 3.31: Texture segmentation. (a) The image to be segmented. (b) After closing by
the size of the small blots. (c) After further closing by the size of the spaces between the
large texture blots. (d) The boundary seen in (c). (e) The boundary superimposed over the
original texture image.