Figure 2.
Diagram illustrating the different combined threshold methods. (A1–4) A closing morphology filter of a 1-pixel radius was applied; then, 4 different local threshold methods were analyzed, mean, median, Otsu and Phansalkar. (B1–4) A closing morphology filter of a two-pixel radius was applied; then, four different local threshold methods were analyzed, mean, median, Otsu, and Phansalkar. (C1-2) Top hat filter followed by a mean or an Otsu local threshold was applied. (D1–3) A bandpass filter that removes pixels ≤2 pixels and >40 pixels followed by a mean or Otsu or Phansalkar threshold was applied. (E1–3) A Frangi filter to identify vessel-like structures was applied, followed by mean or Otsu or Phansalkar local threshold.