Bubbles detected at a window size 40 px (~72 pc), m = 0.3, line density threshold 10, in SMC Hα data. Top: Twelve thresholds between 6 and 2500. Bottom: Twelve thresholds between 3 and 1300 used for the Minkowski map generation. Left: original image opened with a diameter of 3 px (more noise). Right: opening diameter of 5 px (lessnoise). The brightness of the line emission is shown logarithmically within the respective minimum and maximum flux thresholds used for the Minkowski maps (Table 1).