Thermal non-line-of-sight imaging from specular and diffuse reflections

Kaga, Masaki; Kushida, Toshimoto; Takatani, Tsuyoshi; Tanaka, Kenichiro; Funatomi, Takuya; Mukaigawa, Yasuhiro

doi:10.1186/s41074-019-0060-4

Cited by 29 publications

(7 citation statements)

References 9 publications

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“…Using specular reflections requires directly sampling the path from the hidden scene to the relay surface, needing strong assumptions about surface albedo and orientation [Lindell et al 2019a], or placing the scanning system far from the relay surface [Scheiner et al 2020]. Specular reflections produced by infrared wavelenghts have also been utilized for passive NLOS [Kaga et al 2019;Maeda et al 2019b]. These systems are also restricted to reconstructions of planar scenes or to object tracking inside the hidden scene.…”

Section: Related Workmentioning

confidence: 99%

Virtual Mirrors: Non-Line-of-Sight Imaging Beyond the Third Bounce

et al. 2023

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Non-line-of-sight (NLOS) imaging methods are capable of reconstructing complex scenes that are not visible to an observer using indirect illumination. However, they assume only third-bounce illumination, so they are currently limited to single-corner configurations, and present limited visibility when imaging surfaces at certain orientations. To reason about and tackle these limitations, we make the key observation that planar diffuse surfaces behave specularly at wavelengths used in the computational wave-based NLOS imaging domain. We call such surfaces virtual mirrors. We leverage this observation to expand the capabilities of NLOS imaging using illumination beyond the third bounce, addressing two problems: imaging single-corner objects at limited visibility angles, and imaging objects hidden behind two corners. To image objects at limited visibility angles, we first analyze the reflections of the known illuminated point on surfaces of the scene as an estimator of the position and orientation of objects with limited visibility. We then image those limited visibility objects by computationally building secondary apertures at other surfaces that observe the target object from a direct visibility perspective. Beyond single-corner NLOS imaging, we exploit the specular behavior of virtual mirrors to image objects hidden behind a second corner by imaging the space behind such virtual mirrors, where the mirror image of objects hidden around two corners is formed. No specular surfaces were involved in the making of this paper.

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Section: Related Workmentioning

confidence: 99%

Virtual Mirrors: Non-Line-of-Sight Imaging Beyond the Third Bounce

et al. 2023

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“…However, the performance of these methods is often compromised by the significant scattering produced by the rough surface of the wall and the visible ambient light. We and several authors have reported that the use of long-wave-infrared (LWIR) light has several advantages that can reduce these difficulties [16,[17][18][19][20]. First, thermally-elevated objects such as human subjects are seen as light emitters, and these signals stand out amongst the ambient background.…”

Section: Introductionmentioning

confidence: 99%

Maximizing the non-line-of-sight information content retrievable from passive scattered light fields: a comparison between visible, long wave infrared, and terahertz radiation

Sasaki,

Leger

2023

Unconventional Imaging, Sensing, and Adaptive Optics 2023

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We explore the use of plenoptic data for performing passive non-line-of-sight imaging using light scattered from interior hallways at visible, long-wave infrared, and terahertz frequencies. The use of longer wavelength radiation in the LWIR and THz bands can increase the retrievable NLOS image information in comparison to visible radiation. However, significant scattering effects at LWIR wavelengths and diffraction effects at the millimeter wavelengths of THz radiation present unique optical design challenges. In this paper, by assuming a general imaging system for light field capture, we provide a theoretical framework to describe measured NLOS information including scattering and diffraction effects. Our analysis combines a ray-based light field description of the plenoptic space with a Wigner distribution function formalism to provide an intuitive physical understanding of the limits of NLOS imaging. Further, based on the analysis, we provide a simple strategy to design optical measurement systems in the LWIR and THz wavelength ranges.

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“…Over the last decade, various principles have been explored for NLOS imaging, including speckle correlations [4,5], transient imaging [6,7], photon counting imaging [8,9] and intensity imaging [10,11]. Most existing methods exploited how to identify the NLOS scene by using time-of-flight (TOF) of photons information from the backscattered signal [12,13].…”

Section: Introductionmentioning

confidence: 99%

Active mode single-pixel non-line-of-sight imaging system based on second-order correlation and diffraction

Li¹,

Xu²,

Wang³

et al. 2022

J. Opt.

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Non-line-of-sight (NLOS) imaging relies on capturing light that has been weakened due to multiple reflections and recovering the occluded scene with high quality is very challenging. To improve the quality of NLOS imaging, an active mode single-pixel NLOS imaging reconstruction framework based on the second-order correlation function and diffraction inverse operation is proposed. Under the collective effect of illumination pattern and single-pixel detector light intensity, the inverse imaging problem is first solved by a statistically weighted average, and then, an additional process is connected to reduce the influence of diffraction on reconstructed image quality based on the Fourier transform and inverse diffraction operation. The simulation and experimental results show that the proposed method with the Hadamard pattern and diffraction inverse operation, which achieved the SSIM value of 0.9286, is superior to the random pattern at a full sampling rate. The lens aperture size, pattern location, and the number of measurements have a significant effect on the system. Therefore, the proposed scheme has potential practical applications.

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Thermal non-line-of-sight imaging from specular and diffuse reflections

Cited by 29 publications

References 9 publications

Virtual Mirrors: Non-Line-of-Sight Imaging Beyond the Third Bounce

Virtual Mirrors: Non-Line-of-Sight Imaging Beyond the Third Bounce

Maximizing the non-line-of-sight information content retrievable from passive scattered light fields: a comparison between visible, long wave infrared, and terahertz radiation

Active mode single-pixel non-line-of-sight imaging system based on second-order correlation and diffraction

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