The total pore area, macropore area, and coarse mesopore area of an image
was divided by the 2500-mm2 area to estimate porosity (macroporosity
+ coarse mesoporosity), macroporosity, and coarse mesoporosity,
respectively. The fractal dimension of macropores was
determined with 100 as the threshold value, instead of 40, to better
populate the low porosity samples with pores (Gantzer and Anderson,
2002). For all images, the fractal dimension was obtained as the slope
of the log–log plot of measured box counts as a function of box size.