Fig. 1. Simulation setting. (a) Simulation body; (b) simulation energy spectrum generated by Spekpy v2.0; (c) attenuation coefficient of material (from NIST)

Fig. 2. Direct reconstruction results of multi-energy spectrum projection images in 17 intervals. (a) Reconstructed image; (b) attenuation coefficient curve

Fig. 3. Partially reconstructed images obtained by decomposing 5^th, 7^th, 9^th, and 11^th projection images by NMF-GN algorithm and BSS-BE algorithm

Fig. 4. Attenuation coefficient curve and normalized root mean square error of reconstructed image. (a) Attenuation coefficient of 5^th reconstructed image processed by NMF-GN algorithm; (b) attenuation coefficient of 7^th reconstructed image processed by NMF-GN algorithm; (c) change curve of normalized root mean square error with sequence number of reconstructed image

Fig. 5. Direct reconstruction results of multi-energy spectrum projection images in 18 intervals. (a) Reconstructed image images; (b) attenuation coefficient curve

Fig. 6. Partially reconstructed images obtained by decomposing 7^th, 8^th, 9^th and 16^th projection images by NMF-GN algorithm and BSS-BE algorithm

Fig. 7. Attenuation coefficient curves decomposed by NMF-GN algorithm and BSS-LV-BE algorithm. (a) Attenuation coefficient of 8^th reconstructed image at line in Fig. 5(a); (b) attenuation coefficient of 16^th reconstructed image at line in Fig. 5(a)

Fig. 8. Change curves of average attenuation coefficient of different materials with sequence number of reconstructed image. (a) Mg; (b) Al

Fig. 9. Reconstructed images and attenuation coefficient curves of sample 2. (a) Directly reconstructed image under 60 kV voltage; (b) 7^th reconstructed image obtained by NMF-GN algorithm (corresponding energy is 38 keV); (c) 7^th reconstructed image obtained by BSS-LV-BE algorithm; (d)(e)(f) attenuation coefficient of reconstructed image (a)(b)(c) at line of Fig.(a)