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# Grasp and Manipulation of Objects with a Multi-Fingered Hand ...

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3.2 Preparation stages
z
a
1
r
1
p
x
y
z
c
x
c
y
c
a
2
r
2
Figure 3.3: Camera stations (bullets) and trajectories of the camera during the
acquisition of the images.
2. a subset of n
1
images is taken from camera stations equally distributed over
a circular path of radius r
1
, with the optical axis of the camera pointing to
the estimated center of the object and forming an angle
1
with respect to
the revolution axis z;
3. a subset of n
2
images is acquired as in 2), but using a radius r
2
and an angle
2
.
In the following, the total number of acquired images will be denoted as n
img
=
n
1
+n
2
+1. It is worth noticing that not all the previous steps should be performed
to carry out the process of acquisition of the images, but also a subset of the
previous steps can be accomplished.
3.2.2
Elaboration of the images
Once the n
img
images have been acquired on these circular trajectories, the process
of elaboration of these images can start. First, the silhouettes of the images need
to be determined: to this aim, a simple binarization process, with a self-tuned
threshold, has been employed. Then, a process of a binary dilation and erosion
may be necessary to reduce the effects of the image noise and of a not perfect illu-
mination. Moreover, another enhancement of the images can be considered both in
spatial and in frequency domains, with the goal to reduce noise and disturbances
such as the presence of shadows in the views.
27

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Summary :