In oral contrast-enhanced CT colonography, patients are given barium- or iodine-containing solutions to drink to tag out remnants of stool and residual fluid in the colon. Frequently, residual fecal matter absorbs more tagging material and appears much brighter on CT images than surrounding opacified fluid. This may cause even advanced segmentation procedures, like fuzzy connectedness, to miss local regions of colonic lumen. This in turn leads to spurious deformations of the reconstructed colonic wall and impairs interpretation. We show that these problems may be avoided when the properly designed asymmetric affinities are used for segmenting air- and fluid-filled parts of the colon. After this improvement, the segmented volume does not contain holes of missed regions and resulting colonic surface is smooth and free from undesired distortion.