Fig. 1. Comparison results between SPC imaging and other imaging methods^[11]. (a) and (b) Simulation results of phase contrast imaging and SPC imaging, respectively; (c) change of imaging contrast with different phase gradients of objects in two different methods; (d) bright-field image of absorbing sample; (e) SPC imaging result; (f) dark-field image

Fig. 2. Schematic illustration of SPC imaging^[28]. (a) Generic setup of a 4-f filtering system; (b) simulation results of isotropic and curved edge enhancement

Fig. 3. Characteristics and results of an edge enhancement imaging system by inverse design^[36]. (a) and (b) Density plots of the real and imaginary parts, respectively, of the PSF; (c) and (d) amplitude and phase distribution of the spatial filter function; (e) phase object of a panda; (f) experimental result of SPC; (g) experimental result of inverse-designed filter

Fig. 4. Principle demonstration and experimental results of surface plasmonic spatial differentiator^[14]. (a) Incident intensity image; (b) reflected edge detection intensity image; (c) schematic of surface plasmonic spatial differentiator to excite surface plasmon polariton

Fig. 5. Switchable SPC imaging based on photonic spin-multiplexing metasurface^[18]. (a) Schematic of Fourier transform system for spatial filtering; (b) LCP plane wave passing through the metasurface becomes a RCP wave carrying an initial phase; (c) RCP wave passing through the metasurface becomes a LCP wave carrying the vortex phase with the topological kernel of l=1; (d) Gaussian light intensity distribution; (e) intensity distribution of OAM light with l=1; (f) experimental results of 4-f bright field imaging; (g) experimental results of SPC imaging

Fig. 6. Experimental setup and simulation results of metasurface enabled classical edge detection in classical light^[57]. (a) 4-f imaging system based on metasurface using polarization filtering; (b) object target is the “Schrödinger’s cat”; (c) regular mode of a “solid cat”; (d) edge detection mode of an “outlined cat”

Fig. 7. Non-local edge enhancement imaging system with incoherent thermal light^[12]. (a) Phase object; (b) intensity distribution of direct imaging in D2 plane; (c)--(f) edge enhanced ghost images of the phase object with different phase filters; (g) schematic of the thermal light edge enhancement ghost imaging of phase objects

Fig. 8. Full-field, phase-contrast imaging system with non-local edge enhancement^[64]. (a) Experimental schematic; (b) experimental results of the pacman phase object for an increasing number of photons using standard bright field imaging or SPC imaging, respectively

Fig. 9. Quantum switchable edge detection based on metasurface^[57]. (a) Experimental schematic; (b) switch state ON or OFF of the heralding arm. When the idler photons of the heralding arm are projected to |H>, it indicates the switch OFF state and leads to a bright field mode. While the idler photons are projected to |V>, it indicates the switch ON state and leads to an edge detection mode; (c) and (d) calculated and experimental results of regular images, respectively; (e) and (f) calculated and experimental results of edge enhanced images, respectively

Fig. 10. Experimental results of quantum edge enhancement imaging based on VPP^[28]. (a) Standard bright field image of a cat pattern; (b) isotropic edge enhanced image using OAM filter of topological charge l=1; (c) curved edge enhanced image using OAM filter of topological charge l=2. (d) standard bright field image of a pacman pattern; (e)--(f) images of shadow effect from horizontal and vertical directions, respectively, arrow indicates the shadow direction; (g)--(i) comparison of edge enhanced image results with different working modes, corresponding to photon counting mode, traditional light intensity mode and internal trigger mode, respectively. The color bars on the right side of all images represent different photon counts

Fig. 11. SPC up-conversion imaging based on second-order nonlinear processes. (a) Schematic diagram of nonlinear SPC imaging^[68]; (b) experimental results of nonlinear edge enhancement of phase objects^[68]; (c) experimental results of nonlinear edge enhancement of intensity objects^[73]; (d) different field of view changes of edge enhanced images by adjusting crystal temperature for changing phase mismatch^[73]