Master Thesis - Fachbereich Informatik

A.3. SCAN LINES 139
gray value
400
350
300
250
200
150
100
50
1 scanline (y=61)
1 scanline (y=80)
1 scanline (y=100)
0
0 100 200 300 400
x
500 600 700
(b)
(a)
gray value
400
350
300
250
200
150
100
50
normalized sum of 11 scanlines
normalized sum of all rows
0
0 100 200 300 400
x
500 600 700
(d) (e)
Figure A.1: Comparison of a single and multi scan line approach. (a) Input gray scale image.
(b) Profiles of three selected scan lines at height 61, 80 and 100 respectively. The first two
scan lines pass through the printing leading to strong variations in the profile. Compared to
these variations the poor contrast of the right tube border makes a correct detection difficult.
(c) The normalized sum of several scan lines reduces the effect of the printing bringing out the
location of the tube much more clearly. It can be seen that 11 scan lines equally distributed
over the global ROI are sufficient to yield almost equivalent results as if considering every row.
(Note: The profile of the 11 scan lines is shifted since the global ROI included parts of the
guide bars at the upper and bottom row. Since these pixels have a value near zero, they do not
contribute much to the profile sum but are considered in normalization. The scale, however,
does not affect the actual tube location.) (d) Wrong detection of the tube boundaries if using
a single scan line. (e) Result of the multi scan line approach.
(c)