Detecting Colored Fiber Contaminants in Wool Top Using Balanced Illumination

Abstract

Balanced illumination techniques have been used for many years to improve the detection efficiency for colored fiber contaminants in a white fiber mass, e.g., white wool top. The individual fibers in a mass of white wool are essentially transparent, and their images can be partially suppressed by a suitable choice of illumination to increase the contrast of the colored fibers. This paper uses geometrical optics to explain the partial suppression of images formed by transparent fibers under balanced illumination. The paper also shows that these images can be completely suppressed in the ideal situation, where transparent fibers with circular cross section are completely surrounded by a uniformly diffuse source of illumination. The performance of a balanced illumination system can be optimized by choosing illumination conditions that conform more closely to this ideal situation.

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