Structural similarity (SSIM) has been widely used as an important index in the similarity assessment for infrared targets and background, because it is consistent with the theory of the Human Visual System. However, the applicability of the SSIM for infrared image is not clear. Utilizing SSIM alone to assess the similarity for infrared image without any preconditions may result in inaccurate and invalid assessment result, particularly in cases where there are significant variations in imaging conditions and complex background. The study, which aims to illustrate the applicability of SSIM for infrared image, takes the actual imaging process of the infrared optical system into account. Two sets of mid-wave infrared images with different integration time were acquired for simulation analysis. The impact of difference in image contrast and luminance on SSIM is analyzed. The results reveal that, when the imaging conditions of heterologous infrared images are similar, SSIM can provide a more accurate similarity assessment result. However, difference in imaging conditions may lead to significant difference in contrast, luminance, and spatial distribution of infrared images, SSIM cannot assess the similarity for infrared image accurately. The difference will directly affect the accuracy of the similarity assessment between targets and background. Therefore, to ensure the accuracy of SSIM index, it is necessary to ensure that the imaging conditions are the same or similar.
KEYWORDS: Convection, High power lasers, Amplifiers, Thermal effects, Technetium, Laser amplifiers, Temperature metrology, 3D modeling, Optoelectronics, Surface roughness
Thermal effect becomes more prominent in the laser gain medium, to overcome this problem, the forced convective heat transfer with reliability and durability is widely used. The hydro-structures of dimensions of the flow channel affect the thermal performance immediately and efficiently. In this paper, with proposed cooling configuration based on longitudinal forced convective heat transfer, the factors of flow rate, state of flow field and surface roughness are investigated. The results reveal that fully developed flow state, higher flow rate and rougher surface lead to a better cooling capability. In the simulation results with 30 L/min flow rate, the calculated averaged convective heat transfer coefficient is as high as 104 W/m2 ·K, and with slightly fluctuations in fully developed flow period.
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