Figure 4.

Broadband performance and robustness of the proposed approach. Experimental results at the wavelengths of (a) 500 nm, (b) 550 nm, (c) 575 nm, (d) 600 nm, (e) 640 nm and (f) 700 nm. (g) Experimental setup to characterize the hidden image for long-distance propagation. (h) Obtained image after propagating 4 m in free space. Scale bar: 500 μm. Images a–e were captured by a color CCD with 1024 × 768 pixels. Images f and h were captured by a monochrome CCD with 1280 × 1024 pixels.