Full text: Mapping without the sun

Lu Dehao 
Huazhong University Science and Technology, Control Science & Engineering, Wuhan, China 
KEY WORDS: foreign fibers, multi-wavelength imaging system, optimal light energy, optimal wavelength, image fusion 
The objective of this research was to develop a multiwavelength imaging system (MIS) for detecting foreign fibers in the spectral 
region from 405 nm to 940 nm. After determined an optimal wavelength for detecting a certain kind of foreign fiber, the 
multiwavelength images were captured using a multispectral CCD camera at different optimal wavelength source of illumination. An 
image fusion algorithm based on wavelet analysis was created to acquire complete information on foreign fibers. Imaging Results 
showed that the combination wavelengths of 405 nm and 850 nm were the most appropriate for detection of a wide range of foreign 
fibers in cotton. 
The contamination of foreign fibers with polypropylene, hair, 
plastic film, which looks virtually white in their appearance as 
cotton fiber is a major problem in the textile industry [1.2]. As 
the cotton goes through physical processing, the foreign fibers 
are fibrillated finer and finer and thus become more difficult 
to detect and remove. Currently, although the method of 
manual sorting foreign fibers is widely used, it is 
time-consuming, labor-intensive and is not as reliable. Then, 
developing an automated foreign fiber detection system is 
urgent for providing better quality and reducing potential 
economic losses in textile field. Recently, various approaches 
based on visible light image analysis have been tried for 
detecting these foreign fibers. For example, attempts were 
made by P. Tantaswad and Tae Jin Kang using color image 
analysis method to detect impurities in cotton [3.4]. However, 
the use of color scanner and more sophisticated image 
analysis technique was failed to detect the colorless foreign 
fibers and accordingly it was not successful in assessing the 
grades of cotton [5.6]. Research on fiber type identification by 
J.S.Church and Wu RongHong has been carried out using 
NIR absorption characteristic analysis [7.8]. Although this 
method is effective to test the single type of fiber sample, it is 
ineffective to separate the foreign fiber from the background 
of cotton. Ajay Pai proposed the utilization of x-ray 
microtomography system to detect cotton trash [9], but it is 
hardly accepted because of the high-cost measurement system, 
and therefore, sale promotion of this system is not successful 
in most Chinese cotton factories. 
In this study we have investigated how multispectral imaging 
can be used for detection of foreign fibers from cotton. Since 
foreign fibers present different reflectance values in 
comparison to those from cotton fibers in different 
wavelength, we determined the optimal wavelengths for 
detection of each type of foreign fiber using spectral imaging. 
Furthermore, the optimal imaging parameters such as 
wavelength and light energy of the LED array source of 
illumination was quantitatively analysis for achieve obvious 
image features of foreign fibers. The results indicate that the 
image features of foreign fibers differ sufficiently from those 
of cotton fibers in the multispectral imaging system, and the 
method shows promising results. 
In general, the foreign fibers were divided into two categories, 
the colored foreign fibers and colorless foreign fibers. 
Colorless foreign fibers cannot be distinguished visually from 
cotton, but are of a different type of substance from cotton. A 
frequently occurring foreign fiber is, for example, white hair 
look virtually white in their nature form. However, the 
chemical composition between cotton and white hair are 
different, so it is possible to distinguish the two kinds of fibers 
from one another at specific wavelength by their different 
specific absorption of this band light source. Then it is 
reasonable to hypothesis that absorption characteristic may be 
used as an effective discriminable feature between these 
For detection of these foreign fibers, the light range can be in 
the UV (200-400 nm), VIS (400-700 nm), or NIR 
(700-2500nm). When radiation from the lighting system 
illuminates the fibers, it is transmitted through, reflected, or 
absorbed. These phenomena are referred to as optical 
properties. Here, the optical properties are integrated 
functions of the wavelength of the incident light and chemical 
and physical composition of the fibers. In a reflectance 
imaging system, the spectral reflectance characteristic of 
fibers was transformed to image feature by CCD imaging. By 
selecting the appropriate wavelength and light energy of the 
spectrum, it is possible to separate foreign fibers from cotton 
on the basis of their distinct image feature in a spectral 
imaging system. 
In a reflectance imaging system, the measured values of 
image feature 
are a strong function of wavelength 
and light energy 
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