It needs a triggered time to open or close optical gate of the ICCD. The duration time is defined as irising effect time. Although it only lasts a few nanoseconds and often be ignored by users, it can still interfere with the results in some applications such as fluorescence lifetime imaging and gated imaging. This paper proposes a fitting algorithm to correct the irising effect of the image intensifier. This method obtains fitting matrices of different gates through a series delay images of ICCD. Then through these fitting matrices, the imaging pictures are effectively corrected. The advantages of this method are low cost, high efficiency, and simplicity. The verification experiment of this paper is to write letters with a highlighter. The correction algorithm can clearly restore time-resolve image, and significantly improve the contrast of the image.
Fluorescence lifetime imaging (FLI) plays an important role in detection of different fluorescence substances. However, when background light is strong and image noise is high, FLI is hard to discriminate substances with approximate fluorescence lifetime. An enhanced time-resolved fluorescence imaging method is proposed. In the method, a dual-gated intensity-correlation enhancement algorithm is developed. Compared with traditional rapid fluorescence lifetime determination imaging method, the method focuses on improve image contrast and can effectively remove background noise. It utilizes two fluorescence intensity images at different delay times, and adaptively chooses the filter threshold and the up threshold to remove noise and enhance contrast. The thresholds are determined by the distribution of image variance. In proof experiments, three brands of highlighters with the same color have close fluorescence lifetime, and the proposed method shows their fine fluorescence difference. The simulation and experimental results prove that the method can improve the ability of time-resolved fluorescence imaging.
KEYWORDS: 3D image processing, 3D acquisition, Target detection, Near infrared, Night vision, Stereoscopy, Pulsed laser operation, Gated imaging, Imaging systems, Night vision systems
Traditional NIR laser night vision systems can only obtain 2D images without target range information, and are also easily affected by fog, rain, snow and foreground/background. To solve the problems above, 3D laser night vision based on range-gated imaging has been developed. This paper reviews 3D range-gated imaging advances and focuses on 3D rangeintensity correlation imaging (GRICI) due to its better real time performance and higher spatial resolution. In GRICI systems, the typical illuminator is eye-invisible pulsed semiconductor laser, and the image sensor chooses gated ICCD or ICMOS with mega pixels and ns-scaled gate time. To realize 3D night vision, two overlapped gate images with trapezoidal or triangular range-intensity profiles are grasped by synchronizing the puled laser and the gated sensor. The collapsed range is reconstructed by the range-intensity correlation algorithm, and furthermore 2D and 3D images can both be obtained at the same frame rate. We have established 3D NIR night vision systems based on triangular GRICI, and the experimental results demonstrate that 3D images realize target extraction from background and through windows or smoke. The range resolution minimum is about less than 0.2m at the range of 1km in our GRICI-NV3000, and the range maximum of 3D imaging is about 5km in our GRICI-NV6000.
A method of ns-scaled time-gated fluorescence lifetime imaging (TFLI) is proposed to distinguish different fluorescent substances in forensic document examination. Compared with Video Spectral Comparator (VSC) which can examine fluorescence intensity images only, TFLI can detect questioned documents like falsification or alteration. TFLI system can enhance weak signal by accumulation method. The two fluorescence intensity images of the interval delay time tg are acquired by ICCD and fitted into fluorescence lifetime image. The lifetimes of fluorescence substances are represented by different colors, which make it easy to detect the fluorescent substances and the sequence of handwritings. It proves that TFLI is a powerful tool for forensic document examination. Furthermore, the advantages of TFLI system are ns-scaled precision preservation and powerful capture capability.
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