Graphics Reference
In-Depth Information
Fig. 4.6
Calibration of the
depth from defocus
algorithm: measurements
(Σ
−
1
,(z
−
z
0
))
and fitted
calibration curve
Fig. 4.7
Depth from defocus analysis of a raw forged iron surface. (
a
) Raw measurements.
(
b
) Raw measurements smoothed with a median filter of 30
×
30 pixel size
Wöhler (
2008
) find that the measured
(Σ
−
1
,(z
z
0
))
data points can be represented
fairly well by a linear function (cf. Fig.
4.6
), displaying a nonzero offset due to the
aforementioned imperfections of the optical system. This simple relationship holds
due to the regarded small depth range. For larger depth ranges, more appropriate
representations of the relationship between PSF radius and depth are introduced in
Sect.
4.2.3
.
D'Angelo and Wöhler (
2008
) have acquired images of the raw forged iron sur-
face of a connection rod from a distance of about 450 mm with a lens of
f
−
=
25 mm
×
=
=
focal length at 1032
2, respectively
(the field of view corresponds to 10
◦
). The raw depth from defocus measurements
are shown in Fig.
4.7
a. Smoothing this result by a median filter of 30
776 pixel image resolution for
κ
8 and
κ
30 pixel
size yields the surface profile shown in Fig.
4.7
b, which provides a reasonable im-
pression of the overall surface shape. However, the profile shows many spurious
structures, especially on small scales, such that shape details are not reliably re-
covered. The standard error of the depth values obtained by depth from defocus
corresponds to 1
.
2mm(cf.Fig.
4.6
), with an average object distance of 450 mm.
×
Search WWH ::
Custom Search