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Improving terahertz imaging by light field processing

XIN Tao PENG Shuo DONG Liquan ZHANG Shaohui ZHANG Cunlin

辛涛, 彭烁, 董立泉, 张韶辉, 张存林. 基于光场处理方法的太赫兹成像优化[J]. 中国光学(中英文). doi: 10.37188/CO.EN.2022-0005
引用本文: 辛涛, 彭烁, 董立泉, 张韶辉, 张存林. 基于光场处理方法的太赫兹成像优化[J]. 中国光学(中英文). doi: 10.37188/CO.EN.2022-0005
XIN Tao, PENG Shuo, DONG Liquan, ZHANG Shaohui, ZHANG Cunlin. Improving terahertz imaging by light field processing[J]. Chinese Optics. doi: 10.37188/CO.EN.2022-0005
Citation: XIN Tao, PENG Shuo, DONG Liquan, ZHANG Shaohui, ZHANG Cunlin. Improving terahertz imaging by light field processing[J]. Chinese Optics. doi: 10.37188/CO.EN.2022-0005

基于光场处理方法的太赫兹成像优化

详细信息
  • 中图分类号: xxxx.xx

Improving terahertz imaging by light field processing

doi: 10.37188/CO.EN.2022-0005
Funds: Supported by Founding of National Key Research and Development Program of China (No. 2021YFC2202400); foundation enhancement program under Grant (No. 2021-JCJQ-JJ-0823); National Natural Science Foundation of China (No. 61735003)
More Information
    Author Bio:

    辛 涛(1971—),男,河北省石家庄市人, 2004 年于燕山大学获硕士学位。工作单位:河北师范大学职业技术学院。主要从事测试计量及太赫兹成像的研究。E-mail:xintao71@mail.hebtu.edu.cn

    彭 烁(1995—),女,博士研究生,2017 年于北京理工大学获得学士学位,主要从事光场成像,三维测量相关研究。E-mail:pengshuoeve@163.com

    Corresponding author: zhangshaohui@bit.edu.cncunlin_zhang@cnu.edu.cn
  • 摘要: 近年来,太赫兹技术在检测,安保等诸多领域变得日益重要。如何扩大视场和提高成像质量是太赫兹成像的关键。针对以上问题,我们基于单相机扫描方式搭建了一个太赫兹光场成像系统以同时实现对太赫兹波空间和角度分布信息的利用。基于四维全光函数和双平面参数化方法,我们利用太赫兹光场传播过程中的强度一致性进行了重聚焦运算,通过对光场进行积分即可得到一系列对应不同视角,不同成像距离的结果。与初始的太赫兹成像结果相比,视场和成像质量都得到了有效提升。在我们的实验中,视场扩大了1.84倍,分辨率从1.3 mm提高到了0.7 mm。此外,部分被遮挡的目标信息也可通过使遮挡物离焦得到恢复。证明了我们的系统能够提高太赫兹成像的质量并拓展其功能,从而为太赫兹无损测量和安全检测提供新的思路。

     

  • Figure 1.  Schematic diagram of the system. (a) the THz camera and the two-dimensional translation stage; (b) the light filter.

    Figure 2.  Parametrization of light field. (a) pairs of points on two parallel plane; (b) parameterization of our system.

    Figure 3.  The resampling diagram of refocusing process. When changing the object distance, the spatial coordinate s of the reference sub-image u0 are constant, while the corresponding object point moves from P to Pα. According to the geometric principles, we can calculate the new coordinate sα of sub-image u, which is different from the coordinate s1 corresponding to P.

    Figure 4.  A rubber ring in an envelope. (grid size 9×3, Du=Dv=10 mm) (a) the rubber ring (outer diameter 25mm; inner diameter 17 mm) and the envelope; (b) the reference sub-image (u=4, v=2); (c) the refocused image (αL=640 mm); (d) normalized gradient image of the labelled regions of (b) and (c) respectively and their gradient values of labelled horizontal lines corresponding to t=197.

    Figure 5.  A steel board with hollowed parts in a plastic box. (grid size 9×1, Du=10 mm) (a) the steel board (length 68 mm; width 45 mm) and the plastic box; (b) the reference sub-image (u=5, v=1); (c) the refocused image (αL=650 mm); (d) intensity of labelled horizontal lines corresponding to t=174.

    Figure 6.  Metal wrenches fixed on a polyvinyl chloride(PVC) board by tape. (grid size 9×7, Du=Dv=10 mm) (a) the wrenches (from left to right the diameters are 0.7 mm, 0.9 mm, 1.3 mm and 1.5 mm) and the PVC board; (b) the reference sub-image (u=3, v=4); (c) the refocused image (αL=610 mm); (d) the refocused image after histogram equalization.

    Figure 7.  Metal wrenches (fixed camera and moving target, grid size 9×5, Du=Dv=10 mm). (a) the wrenches and the PVC board; (b) the reference sub-image (u=5, v=3); (c) the refocused image (αL=624 mm); (d) the refocused image after histogram equalization.

    Figure 8.  Refocusing images of different sub-views (two PVC bottles with liquid fixed by tape in a high-density polyethylene plastic box, grid size 9×2, Du=10 mm, Dv=20 mm). (a) the bottles (length 50 mm; diameter 13 mm; thickness 2 mm) and the plastic box; (b) one primitive sub-image; (c)(d)(e)(f) are the refocused images with angular coordinates (4,1), (4,2), (1,1) and (9,1) respectively (αL=640 mm).

    Figure 9.  Refocusing images of different depths. (a) The image focused on the bottles, αL=640mm. (b) The image focused on the tape and the plastic box, αL=600mm.

    Figure 10.  A steel holed cube blocked by a piece of wire mesh placed between it and the THz camera. (a)(b) are two primitive sub-images showing the wire mesh and the obscured target respectively; (c) is the refocused image.

    Table  1.   coordinate of sample pixels in different subview

    subview(4,1)(4,2)(1,1)(9,1)
    Pixel 1(192,175)(192,138)(248,175)(99,175)
    Pixel 2(238,193)(238,156)(301,193)(145,193)
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出版历程
  • 收稿日期:  2022-03-31
  • 录用日期:  2022-05-13
  • 网络出版日期:  2022-06-10

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