Fig. 1. (a) Experimental schematic of non-iris SSCI system. RD, rotating diffuser; u, 35–50 cm; v, 15 cm; (b) flow chart of the proposed method.

Fig. 2. Experiment results of non-iris SSCI at a scale factor of 0.3. (a1)–(a4) Raw speckle images of different objects; (b1)–(b4) resized speckle images of (a1)–(a4); (c1)–(c4) autocorrelations of (b1)–(b4); (d1)–(d4) images reconstructed from (c1)–(c4) through phase-retrieval algorithm; (e1)–(e4) corresponding original objects. Scale bars, 1 mm.

Fig. 3. Logarithmic speckle autocorrelation and the normalized power spectrum at different scale factors s. (a1) Autocorrelation of the original object, i.e., the ideal autocorrelation; (b1) power spectrum generated from (a1); (a2)–(a5) speckle autocorrelations at different scale factors 0.1, 0.4, 0.7, and 1; (b2)–(b5) power spectrum from (a2)–(a5), respectively; (c1)–(c5) corresponding reconstructed results for (b1)–(b5) through Ping-pong algorithm; (d) normalized frequency spectra of the center rows of (b1)–(b5) (positive frequencies are shown); (e) quantitative evaluation of speckle autocorrelations using PSNR at different scale factors. Scale bars, 1 mm.

Fig. 4. Experimental results with another two cameras and new parameters. (a1)–(a4) Autocorrelations of the resized image by the factor of s at different distances v; (b1)–(b4) images reconstructed from (a1)–(a4) through phase-retrieval algorithm; (c1)–(c4), (d1)–(d4) as in (a1)–(a4), (b1)–(b4) but for different cameras and s. Scale bars, 1 mm.

Fig. 5. Comparison of experimental results by digital resizing and pixel binning. (a1)–(a3) Raw speckle images of symbol “5” at different distances v: (a1)v = 10 cm; (a2) v = 15 cm; (a3) v = 20 cm; (b1)–(b3) resized speckle images (central part is shown) of (a1)–(a3) by different s (0.5, 0.3, 0.25); (c1)–(c3) objects reconstructed from (b1)–(b3) through phase-retrieval algorithm; (d1)–(d3) binned (2 × 2, 3 × 3, 4 × 4) speckle images at the same distance v as in (a1)–(a3); (e1)–(e3) objects reconstructed from (d1)–(d3) through phase-retrieval algorithm. Scale bars, 1 mm.