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24 September 2007 Comparison of different illumination arrangements on capillary image quality in nail-fold
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The purpose of this study was to investigate which illumination arrangement can provide the highest image quality when using a non-invasive cutaneous imaging system to observe capillaries in nail-fold. We captured the microcirculation images with and without a band-pass filter which wavelength is 556 ± 10 nm in front of a 150 Watt halogen lamp. Furthermore, we varied the illumination angle form 90 degree (co-axial light) to 20 degree to evaluate the image quality under different light source arrangements. The image registration function was used to solve the image movement problem which is due to breathing or slightly movement of volunteers or the imaging device. The contrast-to-noise ratio (CNR) is an evaluation factor to quantify the image quality. The dynamic search method was used to find out the skeleton of a vessel and define the foreground and background parameters for calculating contrast. A Gaussian smooth filter was applied to the original images and noise was resulted from differentiating the coefficient of variance (CV) of the original and processed images. As a result, using a green filter in front of a lamp presents the highest contrast-to-noise ratio when the illumination angle is 20 degree. By normalizing the highest CNR to 1, the CNR of other illumination conditions are 0.49 (without filter, 20 degree), 0.39 (with filter, 90 degree) and 0.28 (without filter, 90 degree), respectively. It is concluded that using a green light source with an illuminating angle of 20 degree will provide better image quality than other arrangements.
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Chih-Chieh Wu, Kang-Ping Lin, and Being-Tau Chung "Comparison of different illumination arrangements on capillary image quality in nail-fold", Proc. SPIE 6696, Applications of Digital Image Processing XXX, 669626 (24 September 2007);

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