Fig. 1. (a) Schematic of lens-free speckle image encoding experiment, where Au nanorods were embedded in a PVP film on glass, which is attached to the surface of a CIS; (b) TEM image of Au nanorods; (c) Extinction spectrum of Au nanorods

Fig. 2. Schematic diagram of the flow of the spectral reconstruction algorithm

Fig. 3. (a)-(c) Speckle plots corresponding to incident light at 600 nm, 650 nm, and 700 nm; (d) Waterfall plot of speckle normalized intensity at 650 nm wavelength; (e) Response matrix; (f) Calculated spectral correlation coefficients

Fig. 4. (a) Spectral reconstruction results based on CNN algorithm; (b)-(f) Spectral reconstruction results based on compressive sensing algorithms

Fig. 5. (a)-(c) Test results of transmission spectra of three bandpass filters, 632.8 nm (FWHM = 3 nm), 650 nm (FWHM = 10 nm) and 670 nm (FWHM = 10 nm); (d) LED luminescence spectroscopy test results

Fig. 6. (a)-(c) Waterfall plot of speckle intensity at 650 nm wavelength when single-layer frosted glass, double-layer frosted glass and triple-layer annealed gold particles are used as scattering structures, and the ordinate is the normalization of the CIS readout data to the maximum value of the reading range; (d)-(f) Response matrix; (g)-(i) The black line is the test spectrum of the commercial spectrometer, and the red line is the reconstructed spectrum based on the proposed technology