Porosity Profile¶

The porosity profile is the porosity of each one-voxel-thick slice through the image, plotted against position along an axis. It reveals what a single porosity number hides: layering, gradients, a denser skin near a cut face, or a segmentation that drifts along the scan because of beam hardening or uneven illumination.

Definition¶

For slice \(i\) normal to the chosen axis,

where \(N_{p,i}\) is the number of pore voxels in slice \(i\) and \(A\) the number of voxels in a slice, plotted at the slice's midpoint, \(x_i = i + \tfrac12\) voxels. The image's porosity \(\varphi\) is the mean of \(\varphi_i\) along any axis, and that mean, \(\bar\varphi\), sums the result up. PoreStore computes the profile with PoreSpy's porosity profile.¹

Reading the result¶

• Fluctuation size. In a uniform sample, slice-to-slice scatter shrinks as the slices get larger compared with the pores. Large swings on a wide sample mean large pores or real heterogeneity.
• Edges. A drop or rise in the last few slices often comes from sample preparation: a damaged cut face, or resin at the surface.
• Along the scan axis. A slow trend along the CT rotation axis can be a segmentation artefact. Compare the same axis before and after segmentation.
• Before a flow simulation. Permeability and diffusivity average over the whole sample. A strong layer normal to the flow direction can control the result. See permeability.

References¶