Million frame-rate single-pixel 3D imaging
Fig. 1 Experimental arrangement. (a) Complete diagram of the 2D imaging experimental setup. (b) Single-pixel detection module of the 3D imaging system.
Fig. 2 Imaging results. (a) 2D imaging results at different time instants in a resolution of 256×256 pixels. (b) 3D imaging results at different time instants with a measurement accuracy of over 95%.
Single-pixel imaging (SPI) is a novel imaging technique that has been widely studied in recent years. It retrieves spatial information of the target by using a single-pixel detector with no spatial resolution, minimizing the array size of imaging detector, that has unique advantage of making up for the shortcomings of the existing focal plane arrays (FPAs) imaging technology. It is believed that this SPI technology has great application value in special waveband imaging that array detector technology is underdeveloped or expensive.
After nearly 30 years of study, scientists have made great progress in the development of SPI. Achievements have been made in various applications, including special waveband imaging, e.g. terahertz and X-ray imaging, extremely low-light level imaging and 3D imaging.
However, due to its unique imaging mechanism, imaging speed of SPI is fundamentally limited by the refresh speed of a core device of the system, the spatial light modulator. This limitation constrains the speed of SPI at a slow level, which restricts its application to general imaging scenarios. The advantage of high detection bandwidth of single-pixel detectors cannot be utilized.
To address this problem, researchers at Shandong University propose and demonstrate a time-resolved single-pixel imaging (TRSPI) technology. This imaging technology is designed for high-speed but periodic scenes. It can realize ultrafast sampling of high-speed targets by fully exploring the spatial correlation information between a dynamic scenes and dynamic coded apertures. Based on ultrafast sampling, high-speed targets can be imaged by applying a typical SPI reconstruction. Imaging speed of TRSPI is ultimately determined by the acquisition speed of single-pixel detector. Therefore, an imaging speed of million frame-rate can be easily achieved by only using ordinary photodiodes.
The relevant research results are published in Photonics Research, Volume. 10, Issue 9, 2022 (Wenjie Jiang, Yongkai Yin, Junpeng Jiao, Xian Zhao, and Baoqing Sun. 2,000,000 fps 2D and 3D imaging of periodic or reproducible scenes with single-pixel detectors[J]. Photonics Research, 2022, 10 (9): 2157-2164).
TRSPI proposed in this work can achieve ultrafast imaging not only in 2D but also in 3D imaging by combining of Fourier transform profilometry (FTP). For the general imaging environment, they also propose a digital calibration scheme to ensure the reconstructed image quality (Fig.1).
The final experimental results show that the proposed scheme achieves 2D and 3D imaging with high spatial resolution and high image quality at an imaging speed of 2,000,000 fps (Fig.2).
Dr. Wenjie Jiang believes that the proposed imaging scheme excavates the application potential of SPI, which is of great significance for the development of SPI. On the other hand, this work also provides a powerful alternative for high-speed imaging. In the future, with a combination of high-speed single photon avalanche detector, imaging speed of the proposed scheme is expected to reach trillion frame rate or even higher.
时间分辨单像素相机：实现百万帧频三维成像
图1实验装置图，（a）完整的二维成像实验装置图；（b）三维成像系统的单像素探测模块
图2成像结果，(a) 重构出的代表不同时刻的二维成像结果，成像分辨率为256×256像素; (b) 重构出的代表不同时刻的三维成像结果，测量精度在95%以上
单像素成像是近年来被广泛研究的一种新型成像技术。该技术仅利用不具备空间分辨能力的单像素探测器来获取目标的空间信息，将成像探测器的像素规模压缩到极限，具有弥补面阵成像技术不足的独特优势，被广泛认为在面阵探测器相对不成熟或较昂贵的特殊波段成像中具有巨大的应用价值。
经过科学家们近三十年的研究和探索，目前单像素成像技术已取得了巨大突破和显著进步，特别是在太赫兹、X射线等特殊波段成像,以及极弱光成像、三维成像等。
单像素成像独特的成像机制，其成像速度一直受到另一个核心器件：空间光调制器刷新速度的限制。该限制使得单像素成像速度一直处于较慢的水平，不能适用于普遍的成像场景，更难发挥单像素探测器的高探测带宽这一优势。
为解决上述问题，山东大学信息科学与工程学院孙宝清教授研究团提出了一种时间分辨的超高速单像素成像技术。该成像技术针对高速变化的周期性场景，通过充分挖掘动态场景与动态编码孔径之间的空间关联信息，实现了对高速目标的快速采样。成像速度完全由单像素探测器的采集速度决定，使用普通的光电二极管即可轻松实现百万帧频的成像速度。相关研究成果发表于Photonics Research 2022年第9期（Wenjie Jiang, Yongkai Yin, Junpeng Jiao, Xian Zhao, and Baoqing Sun. 2,000,000 fps 2D and 3D imaging of periodic or reproducible scenes with single-pixel detectors[J]. Photonics Research, 2022, 10 (9): 2157-2164）。
该工作中所提出的成像系统，不仅能够实现快速二维成像，还能结合傅里叶变换轮廓术来实现时间分辨的三维成像（图1所示）。
同时，针对一般成像环境，作者提出了一种数字校准方案来保证重构图像质量。最终实验结果表明，该方案实现了在2,000,000 fps成像速度下的高空间分辨率、高图像质量的二维和三维成像。
蒋文杰博士表示："我们提出的成像方案进一步挖掘了单像素成像的应用潜力，对于单像素成像的发展具有重要意义。另一方面，本工作也为高速成像提供了一种有力的选择方案，下一步是结合高精度量子探测器件和光学测量手段，该方案的成像速度有望达到每秒数万亿帧，甚至更高。"