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Non-line-of-sight imaging


Emerging single-photon-sensitive sensors produce picosecond-accurate time-stamped photon counts. Applying advanced inverse methods to process these data has resulted in unprecedented imaging capabilities, such as non-line-of-sight (NLOS) imaging. Rather than imaging photons that travel along direct paths from a source to an object and back to the detector, NLOS methods analyse photons that travel along indirect light paths, scattered from multiple surfaces, to estimate 3D images of scenes outside the direct line of sight of a camera, hidden by a wall or other obstacles. We review the transient imaging techniques that underlie many NLOS imaging approaches, discuss methods for reconstructing hidden scenes from time-resolved measurements, describe some other methods for NLOS imaging that do not require transient imaging and discuss the future of ‘seeing around corners’.

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Fig. 1: Layout of time-resolved non-line-of-sight imaging.
Fig. 2: First experimental demonstration of ‘looking around corners’.
Fig. 3: Demonstration of the capability of recording light in flight at picosecond timescales for a pulse of light propagating between three mirrors.
Fig. 4: NLOS reconstructions of a hidden room-sized scene.
Fig. 5: Reconstructions of a large scene using the phasor-field virtual wave approach.
Fig. 6: Main detector technologies classified based on spatial and temporal resolution.


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G.W. and A.V. acknowledge financial support from DARPA REVEAL (HR0011-16-C-0025). G.W. is supported by NSF CAREER Award (IIS 1553333), PECASE (ARO, W911NF19-1-0120) and the Visual Computing Center CCF grant (KAUST Office of Sponsored Research). D.F. is supported by the Royal Academy of Engineering under the Chairs in Emerging Technologies scheme and by the EPSRC (UK, grant no. EP/T00097X/1).

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Faccio, D., Velten, A. & Wetzstein, G. Non-line-of-sight imaging. Nat Rev Phys 2, 318–327 (2020).

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