Figure 4. Workflow example. (A) Slice selector; (B) Cartesian cropping; (C) cylindrical cropping; (D) filtered image; (E) and binary form.
With the aim of selecting the optimum threshold value for the glass-bead sample, various calculations were performed on the 3D rendered image, and information regarding porosity, number of clusters, and size of clusters was derived. These calculations were carried out for each of the considered thresholds and are plotted in Figure 5. For this sample, a valley in the number of clusters vs threshold plot is observed between threshold values 0.40 and 0.45. The porosity of the glass beads calculated with Mathematica was found to be 0.378, at threshold value 0.45 located in the valley. On the other hand, Nakashima et al . determined a gravimetric porosity of 0.370 for a glass-bead sample [16]. These results indicate that a threshold value of 0.45 should be optimum for the glass-bead sample. A glass-bead sample is known to have only one pore system, and therefore should consist of a low number of clusters in the PCA (the valley). The results of this experiment indicate that the glass-bead sample can be successfully used as a model to test the Mathematica code.