KEYWORDS: Cameras, Long wavelength infrared, Signal to noise ratio, Prototyping, Super resolution, Modulation transfer functions, Infrared cameras, Image processing, Imaging systems, Infrared imaging
To address the complex structure and bulky volume problem of long-wave infrared detection system, we design a front-and-back-splitting distributed long-wave infrared array camera based on fiber image bundle with a simple and high-flexibility structure. The proposed system achieves higher signal-to-noise ratio and improved resolution using image algorithm processing. Benefited by the fiber bundle, the front and back lens groups are separated, which is conductive to scanning imaging and conformal design. A principal prototype of 2-way synthesis is built to verify the imaging performance of the array camera. The prototype is used to obtain two-aperture time series images of small target. One is used as a benchmark and the other is registered and synthesized. The signal-to-noise ratio of composite image increased by 25.15% by eliminating time noise. Besides, this paper uses the redundant information among multiple micro-displacement images obtained by pixel-level displacement of fiber bundle to achieve super-resolution image reconstruction. The image resolution at least doubles in one-dimensional direction and the reconstruction algorithm can be extended to two dimensions. Experimental results of the prototype show that the distributed array camera we designed can improve the signal-to-noise ratio and realize image super-resolution reconstruction with structure simplified and volume reduced.
Infrared camera arrays have previously demonstrated the potential for long-range detection due to their distributed aperture structures, but their performance is affected by the calibration procedure. The widely used calibration method based on image registration estimates the transformation matrix between different cameras by extracting matching features, and its accuracy is limited by low-resolution infrared images. To solve this problem, a new calibration method based on infinite scene registration is developed, which has high registration accuracy and is easy to implement. The results of the laboratory experiment demonstrate that the signal-to-noise ratio of the point target is improved by 1.86 with the proposed method, which proves the effectiveness and competitiveness of the proposed method. Finally, the measured data of long-range aircraft further verifies the feasibility of the proposed method.
The fiber bundle (FB) optical system is widely used in many fields, such as medical imaging and military reconnaissance, owing to its advantages of high design freedom, small volume, and light weight. The traditional theory for the optical transfer function is not suitable for such a discrete sampling optical system. Researchers have developed numerical calculation methods to analyze the imaging quality of the discrete sampling optical system, in which the geometric model needs to be established and the coupling region needs to be determined. We have developed a simple and computationally efficient imaging theory that is suitable for various combinations of FB and CCD detectors. The coupling modulation transfer function (coupling-MTF) of discrete sampling optical systems of square-arrangement fiber bundles (SFBs) and hexagonal-arrangement fiber bundles (HFBs) are analyzed. Simulation results demonstrate that although SFB has a higher coupling-MTF than HFB, the latter is more convenient in coupling alignment operation. Our results have proven the effectiveness and universality of the proposed theory, and it can be used to guide the system design.
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