Process of extracting the light bridge. (a) Umbra area segmented as described in Sect. 2.4. (b) Umbra area processed by the morphological closing operation. (c) Candidate light bridges before threshold screening of the area. (d) Candidate light bridges screened by the area threshold. (e) Location relation between light bridges and umbras. The white and gray areas represent the light bridge and the umbra, respectively. The green lines represent the areas in which light bridges intersect umbras, and the red lines represent the areas in which the light bridges do not intersect umbras. (f) Final segmentation results of the light-bridge area.