Fig. 1. Schematic diagram of the system. (a) The THz camera and the two-dimensional translation stage; (b) the light filter.

Fig. 2. Parametrization of the light field. (a) Pairs of points on two parallel planes; (b) parameterization of our system

Fig. 3. The resampling diagram of refocusing process. When changing the object distance, the spatial coordinate S of the reference sub-image u₀ are constant, while the corresponding object point moves from P to P_α. According to the geometric principles, we can calculate the new coordinate S_α of sub-image u, which is different from the coordinate S₁ corresponding to P

Fig. 4. A rubber ring in an envelope (grid size 9×3, D_u=D_v=10 mm). (a) The rubber ring (outer diameter is 25 mm; inner diameter is 17 mm) and the envelope; (b) the reference sub-image (u=4, v=2); (c) the refocused image (αL=720 mm); (d) normalized gradient image of the labelled regions of (b) and (c), respectively and their gradient values of labelled horizontal lines corresponding to t=197

Fig. 5. A steel board with hollowed parts in a plastic box (grid size 9×1, D_u=10 mm). (a) The steel board (length is 68 mm; width is 45 mm) and the plastic box; (b) the reference sub-image (u=5, v=1); (c) the refocused image (αL=730 mm); (d) intensity of labelled horizontal lines corresponding to t=174

Fig. 6. Metal wrenches fixed on a polyvinyl chloride(PVC) board by tape. (grid size 9×7, D_u=D_v=10 mm) (a) the wrenches (from left to right the diameters are 0.7 mm, 0.9 mm, 1.3 mm and 1.5 mm) and the PVC board; (b) the reference sub-image (u=3, v=4); (c) the refocused image (αL=680 mm); (d) the refocused image after histogram equalization.

Fig. 7. Metal wrenches (fixed camera and moving target, grid size 9×5, D_u=D_v=10 mm). (a) The wrenches and the PVC board; (b) the reference sub-image (u=5, v=3); (c) the refocused image (αL=700 mm); (d) the refocused image after histogram equalization

Fig. 8. Refocusing images of different sub-views (two PVC bottles with liquid fixed by tape in a high-density polyethylene plastic box, grid size 9×2, D_u=10 mm, D_v=20 mm). (a) The bottles (length is 50 mm; diameter is 13 mm; thickness is 2 mm) and the plastic box; (b) one primitive sub-image; (c)(d)(e)(f) are the refocused images with angular coordinates (4,1), (4,2), (1,1) and (9,1) respectively (αL=720 mm).

Fig. 9. Refocusing images of different depths. (a) The image focused on the bottles,αL=720 mm. (b) The image focused on the tape and the plastic box,αL=670 mm

Fig. 10. A steel holed cube blocked by a piece of wire mesh placed between it and the THz camera. (a) and (b) are two primitive sub-images showing the wire mesh and the obscured target respectively; (c) the refocused image