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An experimental study on terahertz light field data acquisition and digital refocusing
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摘要:
本文对太赫兹光场数据采集与数字重聚焦成像进行实验研究。太赫兹成像因其穿透性、无损性等优点，近年来备受国内外研究者关注。太赫兹波段的光场成像技术有望增强图像质量、改善应用效果。本文在分析光场成像基本原理、系统结构、重建方法的基础上，应用太赫兹焦平面阵列相机进行太赫兹光场数据采集和数字重聚焦实验。首先采集太赫兹光场原始数据，然后通过数字重聚焦进行计算成像，最后对重构图像做增强处理，得到了深度、角度及目标物轮廓分辨力强的太赫兹图像。实验证明了太赫兹光场成像技术的可行性及其改善图像质量、丰富复现效果的能力。
Abstract:In recent years, terahertz imaging has attracted great attention due to its advantages including penetrability and nondestructive property. The field imaging technology within the terahertz range is expected to enhance the terahertz image quality and improve its application effect. In this paper, an experiment on the data acquisition and digital refocusing of the terahertz light field was conducted. Firstly, the basic principle, system structure, and the method of reconstructing light field imaging were analyzed. Secondly, the terahertz focal plane array camera was used to collect the data about light field and digital refocusing was used to get the computed imaging. Finally, the reconstructed image was enhanced to obtain higher depth resolution, angle resolution, and object contour resolution. Experimental results showed the feasibility and ability of terahertz light field imaging to improve image quality and enrich retrieval effects.
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Key words:
- terahertz /
- light field acquisition /
- digital refocusing /
- image reconstruction
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Overview: As a highly versatile computational imaging method, light field imaging has attracted great attention and has rapidly developed in the past 20 years. Light field imaging with visible light has been widely applied. Terahertz radiation has many advantages such as good penetrability and effective bandwidth. The combination of light field imaging and terahertz radiation will enrich the concept of light field imaging.
Firstly, this article introduced the characteristics of terahertz waves, summarized the historical development of light field photography, and analyzed the basic principle of terahertz light field imaging. Based on the method of capturing, 4D light field, the typical light field photography devices are categorized into single scanning imaging camera, camera array imaging, integral imaging, aperture coded, optical mask, etc. The terahertz light field imaging technology, a kind of computational imaging method within the terahertz band, takes advantage of terahertz focal plane array camera to collect a series of target sub-image arrays from different directions and angles, then, uses the digital refocusing to get the computed imaging and image reconstruction technology to obtain image. However, the reconstructed image appears blurry with unclear boundary. In order to reduce adverse effects, the image edge feature was combined with Laplace operator to enhance images, thus obtaining the refocusing images of light field with higher depth resolution, angle resolution, and object contour resolution at different depths.
Experimental results showed the feasibility and ability of terahertz light field imaging to improve image quality and enrich retrieval effects. The successful combination of terahertz radiation and light field imaging technology provides unique characteristics for future research. For example, it overcomes the limitation of traditional visible light imaging by optical lens and sensor or the size of the aperture. Terahertz light filed imaging technology can take advantage of the characteristics of the wave to achieve image in the dark environment. In a word, the light field imaging quality is effectively improved by the above method. It lays a foundation for establish a three-dimensional reconstruction and synthetic aperture imaging algorithm by removing the foreground of terahertz light field imaging.
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图 2 基于Levoy光场渲染理论用四维光场函数表征光场
Figure 2. Light field representation using 4D light field function based on Levoy's light field rendering theory
图 3 光场重聚焦算法与参数示意图
Figure 3. The algorithm and its parameterizations of light field refocusing
图 4 太赫兹光场图像。(a)单张子图像；(b)不同位置与不同角度的子图像阵列
Figure 4. Terahertz light field images. (a) A subimage; (b) Subimages with different positions and angles
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