Example of the area selection and dilation procedure (Sect. 3.2) for NOAA AR 11945. Panel a) shows the selection >40 G in the blurred map of absolute field values. Panel b) shows the selection >20 G and <−20 G in the smoothed signed map (blue), along with the selection from panel a (yellow). Panel c) shows the selection after the field-dependent dilation, and panel d) the final region selection after the field-independent dilation.