Physics

Sight

Non-line-of-sight propagation

Mathematics

Wireless

Optics

Physical optics

Artificial intelligence

Power (physics)

Diffraction

Phasor

Line (geometry)

Geometry

Line-of-sight

Computer science

Astrophysics

Quantum mechanics

Electric power system

Computer vision

Telecommunications

Nature

Non-line-of-sight imaging allows objects to be observed when partially                or fully occluded from direct view, by analysing indirect diffuse reflections off a                secondary relay surface. Despite many potential                        applications1–9, existing methods lack practical usability because of                limitations including the assumption of single scattering only, ideal diffuse                reflectance and lack of occlusions within the hidden scene. By                contrast, line-of-sight imaging systems do not impose any assumptions about the                imaged scene, despite relying on the mathematically simple processes of linear                diffractive wave propagation. Here we show that the problem of non-line-of-sight                imaging can also be formulated as one of diffractive wave propagation, by                introducing a virtual wave field that we term the phasor field. Non-line-of-sight                scenes can be imaged from raw time-of-flight data by applying the mathematical                operators that model wave propagation in a conventional line-of-sight imaging                system. Our method yields a new class of imaging algorithms that mimic the                capabilities of line-of-sight cameras. To demonstrate our technique, we derive three                imaging algorithms, modelled after three different line-of-sight systems. These                algorithms rely on solving a wave diffraction integral, namely the                Rayleigh–Sommerfeld diffraction integral. Fast solutions to Rayleigh–Sommerfeld                diffraction and its approximations are readily available, benefiting our method. We                demonstrate non-line-of-sight imaging of complex scenes with strong multiple                scattering and ambient light, arbitrary materials, large depth range and occlusions.                Our method handles these challenging cases without explicitly inverting a                light-transport model. We believe that our approach will help to unlock the                potential of non-line-of-sight imaging and promote the development of relevant                applications not restricted to laboratory conditions. Algorithms based on diffractive wave propagation of light offer                effective imaging of complex scenes hidden from direct view.

Non-line-of-sight imaging using phasor-field virtual wave optics