Fig. 1. Flow chart of multiple facula/overlapping facula center extraction algorithm

Fig. 2. Input image

Fig. 3. Binary graph after preprocessing

Fig. 4. Connected domain diagram

Fig. 5. Image after edge extraction

Fig. 6. Shape factor varying with oblateness and degree of overlap. (a) Shape factor varying with oblateness; (b) shape factor varying with degree of overlap

Fig. 7. Overlapping facula segmentation

Fig. 8. Spot center extraction results

Fig. 9. Real solar faculae. (a) Image of real solar faculae; (b) cross section of gray value distribution of single solar facula

Fig. 10. Local images obtained by some experiments. (a) Circle faculae obtained by experiment on degree of overlap; (b) ellipse faculae obtained by experiment on degree of overlap; (c) ellipse faculae obtained by experiment on overlapping angle