KEYWORDS: Image enhancement, Color imaging, Optical filters, Light sources and illumination, High dynamic range imaging, Image processing, Image intensifiers
Low-light-level (LLL) real-time color imaging technology plays an important role in military reconnaissance, scientific detection, security monitoring and assisted driving, and is one of the key technologies developed domestically and internationally. When the ambient light is insufficient, the imaging effect of the human eye is reduced. In order to enhance human eye recognition ability under low illumination and obtain imaging effects with real color, high resolution and high sensitivity, more and more teams are committed to researching LLL real-time color imaging technology. Firstly, the impact of human visual limitation and physical constraint on LLL real-time color imaging is analyzed in this paper. Then, the current research progress of LLL real-time color imaging technology is introduced. Finally, according to the future research direction, the problems and key methods that need to be further studied are proposed.
As a temporary substrate for preparing the Al2O3 ion barrier film, the continuity of the organic membrane significantly affects the compactness of the ion barrier film, while the continuity of the organic membrane prepared by water surface spreading method is directly affected by the non-solvent component. In this paper, the effect of ultrapure water, non-deionized water, NaCl solution, NaOH solution and HCl solution as non-solvent component on the compactness of the organic membrane and ion barrier film are studied. The results show that NaCl solution is the best non-solvent component for the preparation the most continuous organic membrane and the most compact Al2O3 ion barrier film.
To enhance the spatial resolution capability of transmission-mode NEA GaAs photocathodes, this study employed a white-light interferometer to measure the surface configurations of photocathode components post thermal compression bonding. Precise fitting of the surface configurations was achieved using Zernike polynomials, successfully deriving the Zernike polynomial coefficients. Further, these calculated results were integrated into optical design software for modeling, aiming to elucidate the relationship between the photocathode's transfer function and surface configurations. The findings clearly indicate that the MTF value corresponding to 60lp/mm remains stable within the 0° and 5° field angles. However, as the field angle extends to 20°, there is a significant decline in the MTF value. Among them, the transfer performance of the plano-concave photocathode decreases most prominently, followed by the flat structure, while the plano-convex structure exhibits the least decline. Overall, this research provides invaluable references for the further advancement of photocathode technology.
This paper proposed a "high-speed imaging + digital processing" evaluation method to solve the problem of scintillation noise of low light image intensifiers under low illumination, which fills the gap in the quantitative evaluation of scintillation noise characteristics under low illumination in China. It was found that the scintillation noise is mainly characterized by scintillations with a diameter over 50μm and a duration of sub-microsecond or less. The frequency and the brightness of the scintillations are used to quantitatively evaluate scintillation noise. The effects of the input illuminance and luminous gain on the scintillation noise of the domestic low light image intensifier were investigated by the proposed method. With the increase of input illuminance, the frequency of scintillation noise increases linearly, and the brightness does not change obviously. As the luminous gain of the image intensifier increases, the frequency of scintillation noise increases linearly, but the rate of increase in scintillation frequency is higher than that of luminous gain increase. Based on the characteristics of scintillation noise, such as size, duration, intensity, and the variation law with various conditions, the scintillation noise of the image intensifier can be further studied. The quantitative evaluation method of scintillation noise based on scintillation noise frequency and average equivalent input electron quantity proposed in this paper is of great significance to the breakthrough of scintillation noise and the improvement of the performance of image tubes under low illumination in the future.
By changing the doping type, the size of the in-built electric field and the band bending of GaAs photocathode material under different varying doping concentration are simulated to discuss the influence of varying doping concentration on the quantum efficiency of cathode.
The underwater photoelectric detection equipment mainly uses 532 nm laser as the light source, and GaAlAs with Al component of 0.63 can obtain the cutoff wavelength near 532 nm, which is an excellent photocathode material to meet the requirement of narrow band spectral response of 532 nm laser. Furthermore, the light absorptance of the cathode can be improved effectively by the quadrangular prism or cylinder nanostructured arrays prepared on the reflection-mode Ga0.37Al0.63As cathode surface, and the maximum light absorptance can reach 96.2% at 532 nm, when the cylinder nanostructured array with a height of 900 nm and a base width of 100 nm. Nevertheless, the Ga0.37Al0.63As cathode with the quadrangular prism nanostructured array is less influenced by the incident angle of light.
In order to study the properties of the organic membrane as the substrate of the Al2O3 ion barrier film, the micro-micromorphology of organic membrane with different thickness was analyzed by step tester and metallographic microscope, and study the influence about the thickness of the organic membrane on the electrical characteristics of the MCP. The experimental results show that as the thickness of the organic membrane increase, the continuity and compactness of the organic membrane increase; and the loss of the current gain of the ion barrier MCP also increase. When the current gain of MCP without ion barrier film was 16000, and the thickness of organic membrane is 121nm, the current gain of the MCP with the ion barrier film was reduced by 94%.
In order to explore the stability of transmissive GaAs photocathode in ultra-high vacuum system, the activation experiment and re-caesiation experiment of transmissive GaAs photocathode were carried out, and the photocurrent curves after CsO activation and after re-caesiation were tested. Experiments show that high and low temperature thermal cleaning is conducive to CsO deposition and forms a stable structure to improve the photoelectric emission capability and stability of the transmissive GaAs photocathode. Although re-caesiation activation can partially restore the photoemission efficiency of the transmissive GaAs photocathode, it will reduce the stability of the activation layer and shorten the lifetime of the transmissive GaAs photocathode.
Images often suffer from low visibility under nonuniform illumination, weak luminance and backlight environment. This paper describes a novel approach to improvement the visualization of poor light conditions. Firstly, we raise the global brightness using an adaptive exponent induced function. To enhance the local detail perception, the local contrast is boosted by contrast preserving which utilizes human vision system model. To not bias from original image, we generate the contrast combined original image and global illuminance enhance output in the gradient domain. To reduce artifacts, the guided filter is employed to estimate the local mean illuminance when transform the contrast. The experimental results demonstrate that our proposed method has a pleasant visual effect and low computational complexity than the state of the arts.
In this paper, we introduce a novel nonuniformity correction (NUC) algorithm for infrared focal-plane array (IRFPA). It is based on layers technique. First, the Rolling Guidance Filter (RGF) is utilized to decompose the raw IR image into a low frequency part and a high frequency part. Then, an adaptive temporal high-pass filter is utilized to filter the high frequency part by making use of the gradient and amplitude of it to estimate the Fixed Pattern Noise (FPN). The proposed scheme use the frames with large displacement to estimate the FPN to alleviate the ghosting artifacts in case of scene moves slowly. At Last, the estimated FPN is subtracted from the pristine image to obtain the correct result. Experiments with synthetic and real IR video demonstrate that the proposed method has better NUC performance and less artifacts than the state-of-the-arts.
The flawed surface of GaAs/GaAlAs heterointerface after wet etching by H2O2 and NH4OH based etch ant was studied in this work. The results showed that the surface of GaAs/GaAlAs heterointerface had convex point, etching pits, pinhole, fog point, and friction scratches were investigated with a etch step measurement. And imprinting the main reasons for the formation of the etching surface defects of GaAs/GaAlAs are the poor quality of epitaxial materials, the contamination of materials surface, the unclear interface of oxidation and doping, the inhomogeneity of concentration and the operation errors. The selective etching of the GaAs/GaAlAs material eliminates some flaws and improves the quality of the etching surface of the GaAs/GaAlAs material.
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