Applications to Industrial Quality Inspection - 3D Computer Vision: Efficient Methods and Applications - page 265

Fig. 6.23 Stereo image pairs
of the star pattern ( left )and
the ring-shaped flange ( right ).
These examples illustrate
that, due to the specular
reflectance behaviour of the
surface, corresponding
surface parts do not
necessarily have a similar
appearance in the images
ences. Due to the small size of the surface defects, the accuracy of the tactile depth
measurement only amounts to 0 . 05 mm. The true depth of the dent 1 is 1 . 2 mm, the
reconstructed depth 1 . 3 mm. Dents 2 and 3 each have a true depth of 0 . 25 mm, while
the corresponding depth on the reconstructed surface profile amounts to 0 . 30 mm
and 0 . 26 mm, respectively. On large scales, our three-dimensional reconstruction
correctly displays a flat surface. These comparisons indicate a good correspondence
between the true surface and our reconstruction results.
6.3.4 Inspection Based on Specular Stereo
In this section the specular stereo method of Wöhler and d'Angelo ( 2009 ) described
in Sect. 5.4 is applied to the three-dimensional reconstruction of rough metallic
surfaces displaying a weak diffuse reflection component along with considerable
specular lobes and spikes. The same experimental setup as in Sect. 6.3.3.2 is used.
The surface of the connection rod, a cast iron surface displaying a star pattern, and
the ring-shaped surface part of the flange are examined. The first and third examples
have also been regarded in Sect. 6.3.3.2 . The presentation in this section is adopted
from Wöhler and d'Angelo ( 2009 ).
6.3.4.1 Qualitative Discussion of the Three-Dimensional Reconstruction
Results
Figure 5.20 displays a stereo image pair of the connection rod, while in Fig. 6.23
the stereo image pairs of the star pattern and the ring-shaped flange examples are
shown. The appearance of the surface of the star pattern differs so strongly between