Figure 2. Schematic of the proposed multispectral single pixel imaging (MSPI) system.

The broadband light from a bulb is spatially modulated by a spatial light modulator (SLM) to generate a series of 2D random illumination patterns. Next, the spectra of these 2D patterns are stretched into a rainbow stripe using a diffraction grating and a set of lenses. Then the rainbow spectra are modulated by a rotating film before transformed back to 2D spatial patterns. After both the spatial and spectral modulation, the incident illumination is tailored structurally in three dimensions—random in the 2D spatial dimensions and sinusoidal along the spectral dimension. Then the patterns illuminate the target scene to encode both its spatial and spectral information. Finally a bucket detector is utilized to record the correlated lights. In the subsequent reconstruction process, different spectral response signals are decoded by Fourier decomposition, while the spatial information are demodulated by a compressive sensing based reconstruction algorithm. Details of the modulations and demodulations are shown in the insets.