Results are presented as B-scan images. Figs. 5–7 in-
clude the B-scan results for the same cut of the three in-
spected samples. The figures show only a small area of
the cut. These images have been processed by means of
an iso-amplitude contour detection algorithm in order to
enhance the differences between the samples. When com-
paring the three figures, the size of the areas bounded by a
contour line is decreasing from Figs. 5–7. This is because
the increase in porosity of the less dense samples makes
the propagating ultrasonic wave to undergo much more
reflections, and this causes further changes in contour
images. In order to evaluate density, the number of
changes that occur should be determined.