Fig. 1. Symbol meaning diagram

Fig. 2. Diagrams of ascending and descending parts. (a) Ascending parts; (b) descending parts

Fig. 3. Diagrams of the end part. (a) Ascending end; (b) descending end

Fig. 4. Searching results of unimodal curve boundary

Fig. 5. Searching results of multimodal curve boundary

Fig. 6. Experimental results^[24]. (a) Argon arc plasma; (b) Moiré fringe

Fig. 7. Boundary searching results. (a) Intensity; (b) refractive index

Fig. 8. Experimental results^[25]. (a) Propane-air flame; (b) Moiré fringe

Fig. 9. Boundary searching results. (a) Intensity; (b) refractive index

Fig. 10. Result of regional division of argon arc plasma. (a) Intensity; (b) refractive index

Fig. 11. Result of regional division of propane-air flame. (a) Intensity; (b) refractive index