Acquisition and analysis of three–component digital images of soil pore structure. I. Method

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Abstract
SUMMARY: Techniques for examining pore structure as a three–component system, most notably dye–staining of pore space, are reviewed. A method for analysing digital images of pore structure with three components is presented. The method is a direct extension of earlier work on the description of pore structure using two‐component digital images in which the two components represented pore space and soil solid. A previously published method for preparation of an undisturbed, vertically oriented, planar face through soil with pore space in the field condition is used. Field impregnation with opaque epoxy resin is followed by sawing, completion of the impregnation under vacuum and grinding of the sawn face to a smooth finish. In the method presented here the resin used for the laboratory impregnation contains a different‐coloured dye from that used in the field. The ground face is then video‐digitized. Three components are represented in the resulting digital grey level image, namely, field‐impregnated pore space, laboratory‐impregnated pore space and soil solid. The image–processing steps required to segment the grey level image into the three required components are described. Image analysis, for quantitative assessment of the pore structure, consists of generation of 11 pore‐structure attributes from the segmented image. Interpretation of these attributes and use of the method are discussed.