Fig. 1. Coal samples (a) and gangue samples (b)

Fig. 2. Hyperspectral imaging system (a) and process of spectrum extraction (b)

Fig. 3. The original spectral curves in the range of 474~940 nm (a) and 1 235~2 477 nm (b)

Fig. 4. The process of variable selection by CARS in the spectral ranges of (a) Vis/NIR and (b) NIR

Fig. 5. The results of variable selection by SPA over the spectral ranges of (a), (c) Vis/NIR and (b), (d) NIR

Fig. 6. Grayscale images of some samples and corresponding classification visualization
red: Coal; blue: Gangue