Fig. 1. Image of GWAC(clear night without moon). (a) Original image; (b) gray histogram; (c) histogram main peak

Fig. 2. Image of GWAC (thin clouds). (a) Original image; (b) gray histogram; (c) histogram main peak

Fig. 3. Experimental result. (a) Original image; (b) processing result

Fig. 4. Experimental result. (a) Original image; (b) processing result

Fig. 5. Experimental result. (a) Original image; (b) processing result

Fig. 6. Experimental result. (a) Original image; (b) processing result

Fig. 7. Experimental result. (a) Original image; (b) processing result

Fig. 8. Meaning of gray levels in each processing result

Fig. 9. Effect verification for FCM. (a) Image for processing; (b) image for contrast; (c) processing result; (d) cross-match result

Fig. 10. Histograms of DeltaMag by cloud level. (a) Cloud level 1; (b) cloud level 2; (c) cloud level 3; (d) cloud level 4; (5) cloud level 5