When applying image analysis to structure studies we need to choose a concrete method of segmentation of image points pertinent or not to given objects. This study presents the algorithm of tomographic images of aggregated soil to be binarised, created on the basis of the condition of equal structure porosity calculated on the tomogram before and after the segmentation. Moreover, the study provides a method for calculating the structure porosity by means of tomogram generated image. To apply it we need to know the Hounsfield coefficient characterising selected soil aggregates. This coefficient is assumed to amount to the maximum of the set of Hounsfield coefficient values which correspond to locations of local maximums of Hounsfield coefficient histogram. We have assumed the same values of the Hounsfield coefficient for original and compressed soil (relative compression — 13%).