Sample of different types of pores panels a)–g) extracted from the full-sized G-band images. The images are displayed in the range 0.4−1.4 I₀. Major tick marks are separated by 2 Mm. The application of a Perona-Malik filter to the G-band image in panel g) is shown in panel h). This filter facilitates the extraction of pores by intensity thresholding. The contours of the pores are marked by solid lines in panel h). Characteristic parameters of the pores are given in Table 2.