The transform W^(b) is able to detect vessels oriented at the angle direction 0o, which can be better understood by observing the resulting |W^(b)| of Figure 5.6, which was obtained from the retina image of Figure 5.2b for 0= 0° . As can be seen, the horizontally oriented vessel segments have been detected by the Morlet wavelet. Figure 5.6b-d shows the analogous results for 0 = -30°, -60° and -90°, respectively. To segment the blood vessels, the scale parameter was held constant and a series of transforms was calculated for a set of orientations 0 = 0, 10, 20, 30, ..., 180°. We label these transforms as Wp(b), W^, 10(b),..., W^ 180(b), respectively.
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