Fig. 1. Diagram of traditional optical imaging for imaging same target at different detection distances

Fig. 2. Passive ranging and refocusing method based on two-frame detection signals. (a) Schematic of passive ranging based on two-frame detection signals; (b) architecture of passive ranging and refocusing based on two-frame detection signals

Fig. 3. Signal processing and distance solution of coarse ranging method based on two-frame detection signals and IQEF

Fig. 4. Image reconstruction results and edge images corresponding to the first frame detection signal. (a) Image recorded by detector when $z=$253.0 mm; (b) CS reconstruction results based on PSF measurement matrix at different detection distances; (c) edge images corresponding to (b)

Fig. 5. Image reconstruction results and edge images corresponding to the second frame detection signal. (a) Image recorded by detector when detection distance is $z=$254.0 mm; (b) CS reconstruction results based on PSF measurement matrix at different detection distances; (c) edge images corresponding to (b)

Fig. 6. Normalized IQEF curves obtained by two-frame detection signals

Fig. 7. Curves of IQEF in different PSF searching steps

Fig. 8. Curves of IQEF in different axial distance differences$\mathrm{\Delta }z$

Fig. 9. Validation of precision ranging algorithm based on orthogonal constraint. (a) Image reconstruction results without orthogonal constraint; (b) image reconstruction results with orthogonal constraint

Fig. 10. Tomographic image reconstruction results based on TVAL3+OC in different tomographic steps. (a) Reconstruction results corresponding to PSFs of 252.45, 252.8, and 253.15 mm with a tomographic step of $\mathrm{\Delta }L/\mathrm{4}$; (b) reconstruction results corresponding to PSFs of 252.62, 252.8, and 252.98 mm with a tomographic step of $\mathrm{\Delta }L/\mathrm{8}$; (c) reconstruction results corresponding to PSFs of 252.71, 252.8, and 252.89 mm with a tomographic step of $\mathrm{\Delta }L/\mathrm{16}$; (d) reconstruction results corresponding to PSFs of 252.755, 252.8, and 252.845 mm with a tomographic step of $\mathrm{\Delta }L/\mathrm{32}$; (e) reconstruction results corresponding to PSFs of 252.778, 252.8, and 252.822 mm with a tomographic step of $\mathrm{\Delta }L/\mathrm{64}$

Table 1. TVAL3+OC algorithm scheme

Table 2. Distance decoupling based on MSE evaluation