<p>In this study, drainage and imbibition morphologies were quantitatively evaluated during a water retention test using X-ray computed tomography (CT) scanning and image analyses. Drainage and imbibition clusters were extracted by subtracting two CT images with different saturation states after image registration of the CT images, which accounted for the differences in position and size, using affine transformation. By examining the shape complexity and configuration of the drainage and imbibition clusters within the pores, it was revealed that, during the drying process, relatively simple drainage occurs from the pore centers. In contrast, during the wetting process, complex water imbibition occurs from the surface of the soil particles at high suction levels, followed by simpler shape imbibition in the pore centers, filling up the pores at low suction levels. Furthermore, a theoretical water retention curve model, with an assembly of unit cells that can express scanning curves, was constructed by appropriately modeling pore draining and water filling based on the findings obtained from the image analyses.</p>