Fig. 1. Basic configuration of the non-line-of-sight imaging lidar

Fig. 2. Experimental results of non-line-of-sight imaging with glass window^[10-11]. (a) Diagram of light path; (b) Experimental scenario; (c) Imaging results of a person; (d) Imaging results of license plate

Fig. 3. Experimental results of non-line-of-sight imaging with different mirror surfaces^[12]. (a)-(d) Position map of the detector, light source, target and the intermediate reflective surface and target respectively; (e)-(h) Experimental results of mirrors with different materials

Fig. 4. Experimental results of non-line-of-sight imaging with glass under different background lights^[15]. (a) Schematic diagram of the experimental scene; (b1)-(b5) Experimental results under different conditions

Fig. 5. Experimental results of non-line-of-sight imaging using streak camera^[1-2]. (a) Schematic of system principle; (b) Acquired raw data; (c) Reconstructed image; (d) Photo of hardware prototype

Fig. 6. Experimental results of non-line-of-sight imaging using ICCD^[17]. (a)-(c) Results of point lighting experiment; (d)-(f) Results of surface lighting, from left to right are top view, side view, 3D panorama

Fig. 7. Experimental results of non-line-of-sight imaging using PMD^[18]. (a) Scene; (b) System; (c) Lighting source; (d) Target; (e) Intensity image; (f) Depth image

Fig. 8. Experimental results of non-line-of-sight imaging using single pixel of SPAD ^[21]. (a) Experimental setup; (b) Reconstructed image

Fig. 9. Results of non-line-of-sight target detection using SPAD array ^[22] . (a) Experimental setup; (b) Diagram of target location

Fig. 10. Experimental results of non-line-of-sight target location and velocity measurement using SPAD array^[23]. (a) Schematic diagram of target location experiment; (b) Schematic diagram of velocity measurement experiment

Fig. 11. Experimental results of pre-occlusion non-line-of-sight imaging ^[27]. (a) Experimental configuration; (b) Raw data in the absence of an occluder; (c) Raw data in the presence of the occluder; (d) Reconstructed image in the absence of an occluder; (e) Reconstructed image in the presence of the occluder

Fig. 12. Confocal non-line-of-sight imaging system based on Light Cone Transform (LCT)^[28]. (a) Schematic diagram of principle; (b) Experimental setup; (c) Reconstructed image

Fig. 13. Confocal non-line-of-sight imaging experimental results based on frequency-wavenumber migration(f-k Mig)^[29]. (a) Experiment scene; (b) Line-of-sight view; (c) Measured data; (d) Reconstructed image

Fig. 14. Experimental results of non-confocal non-line-of-sight imaging experiment result based on phasor-field virtual wave^[30]. (a) Imaging system; (b) Target; (c) Reconstructed image

Fig. 15. Experiment results of scanning non-line-of-sight imaging with SPAD linear array^[32]. (a) Imaging system, scene; (b) Restored 3D images by different pixels, respectively

Fig. 16. Experiment results of dual scanning non-line-of-sight imaging system^[33]. (a)-(g) Experiment scene and system; (h), (i) Imaging results

Fig. 17. Processing results of the fast back projection algorithm^[36]. (a) Normal back projection algorithm; (b) Fast back projection algorithm; (c) Target; (d) System

Fig. 18. Processing results of the optimization algorithm considering the direction of the target surface and the occlusion between the targets^[41]. (a) Measured data; (b) Linear optimization reconstruction; (c) Improved optimization reconstruction

Fig. 19. Processing results of the LCT algorithm and other algorithms^[28]. Processing results of back projection(a), filtered back projection(b), LCT(c), and LCT+ optimization(d)

Fig. 20. Processing results comparison of frequency wave vector migration(f-k Mig) and other algorithms^[29]. Processing results of target(a), measurement data(b), filtered back projection(c), LCT(d), f-kMig(e)

Fig. 21. Processing results of the phasor-field virtual wave algorithm^[30]. Processing results of confocal LCT (a), filtered back projection (b), virtual wave (c)

Table 1. Main performance parameters of a typical non-visual imaging system

Table 2. Performance comparison of different NLOS imaging algorithms