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Mapping without the sun
Zhang, Jixian

and light energy e when assumed that other imaging
parameters are constant, which described as following,
g = H(A,e) (l)
Çj)r dach specific type of foreign fibersgthe' optimal wavelength
°P‘ anithé optimal light energy opt for the maximum
contrast 5 opt between foreign fibers and cotton are achieved
in the following equation,
g, P ,‘=H(Âj,e op ;) (2)
Thus, we can define the OOP (optimal operating point)
including the optimal wavelength and the optimal light energy
for any type of detected foreign fibers, where image features of
foreign fibers are most distinct in the spectral imaging.
At different optimal operating point, we can capture the
KÂ, ' c
different optimal image opl ’ npl for respectively
detected foreign fibers. And, given the number of the types of
foreign fibers is ^ , it is reasonable to hypothesis that we can
get the optimal image group ^ at ^ different OOP.
AV’O) < 3 >
Then the fused information from different optimal images was
considered, which provide complete information for a wide
range of foreign fibers. Also, the detailed features of foreign
fibers were enhanced using image fusion method. In this paper,
the wavelet-based image fusion approaches was described as
where > I op! represents I(A op ‘,e op ‘) respectively,
and F wavelgt is function of wavelet images fusion.
Thus, a multiwavelength image collection system can be
implemented by the images fused method, according which
each acquired image at the optimal operating point was fused
into the single image, so the fused feature in the single image
can greatly enhance our capability to identify the foreign fibers
from the background of cotton.
Since the image features of foreign fibers are a function of
wavelength and light energy, we set out to find the optimal
wavelength and optimal light energy for these detected
foreign fibers. That is to say, we need to establish several
optimal operating points for the multiwavelength imaging
system to detect these foreign fibers.
The light source used in the multiwavelength imaging system
was LED array, which emitted different wavelength in the
visible and NIR region. Seven discrete bands, whose center
wavelength at 405nm, 470nm, 520nm, 580nm, 630nm, 850nm,
and 940nm were available. Also, the multispectral CCD was
sufficient sensitive to the band from 400nm to 1 lOOnm.
Six kinds of foreign fibers including hair, knitting, jute,
plastic, wool, and bristle were chosen for this experiment. The
choice of these foreign fibers over other types is justified
because they cannot not only be distinguished visually from
the background of cotton, but also they frequently and readily
survive the ginning process and show up in the yam even the
finished fabric. Sample of six kinds of foreign fibers were
placed on the surface of cotton and then presented to the
spectral imaging system at deferent wavelength.
To evaluate the potential of each available wavelength and
light energy for discriminating foreign fibers from cotton, the
image feature discrimination between cotton and foreign
fibers at different OOP was computed.
In the spectral imaging experiment, light energy coefficient
g —
was defined as , where g represents the average
gray level of an image. And feature discrimination was
defined as the gray level difference between foreign fibers
and cotton. Through the experiment, the OOP for each type of
foreign fibers was quantitatively presented in table 1.
Table.l indicated that different foreign fibers have the
different OOP for detecting them over the spectrum (405nm
to 940nm). Clearly, the band at 405nm could be an
appropriate wavelength for detection of jute, knitting, wool,
and bristle, but it is not effective to detect hair, plastic.
Furthermore, these foreign fibers have the different light
energy for detecting them despite the same detection
wavelength. At the same time, the most distinctive different
between hair, plastic and cotton occurred in the band at
850nm. It is therefore clear that either the 405 or 850 nm
wavelength as a center band can be used for the determination
of foreign fibers on cotton in this study. For each specific type
of foreign fibers, we can find the optimal wavelength and
light energy to detect them.
Foreign fibers
Center wavelength Light energy
Table 1 the optimal operating point for detecting foreign
Based on the above results, two optimal bands for use in a
multiwavelength detection scheme were selected. Table 1
summarized the band at 405nm and 850nm were optimal
wavelength for detecting the six types of foreign fibers.
Although there are no single waveband images that can be
used easily to differentiate foreign fibers from cotton, it is
possible that the fused image of the two bands, which have