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100 Chapter 3 ■ Digital Morphology

(Figure 3.9e). There are now gaps in the image where the lines used to be,
but otherwise the music symbols are free of the lines. A further morphological
step can fill in some of the gaps (Figure 3.9f).

(c) (d)

(a)

(e) (f)
(b)
Figure 3.9: Morphological removal of staff lines from printed music. (a) The original
image. (b) The structuring element. (c) Result of the erosion of (a) by (b). (d) Result of
dilating again by the same structuring element. (e) Subtract (d) from (a). (f) Use a simple
morphological operator to fill in the gaps.

3.3.4 Implementation of Binary Erosion
As was done previously in the case of dilation, the implementation will consist
of a program that creates an eroded image given an input image and a
structuring element, and a function that does the actual work. The program is
in the same style as BinDil, and is called BinErode:

BinErode
Enter input image file name: squares.pbm
Enter structuring element file name: simple.pbm
Enter output filename: xx.pbm
The PBM file for the structuring element of Figure 3.9b would be:

P1
#origin 1 0
316
11 1
00 0
00 0
00 0
11 1
00 0
00 0
00 0
11 1
00 0