An image processing system in which sets of image elements having display values outside of a target range B of display values are each respectively morphologically dilated. The intersection between the morphologically dilated sets of image elements is then identified and those image elements within the intersecting region are removed from the set of image elements having the target range B of display values. This removes image elements incorrectly appearing to have display values corresponding to the target range B of display values due to aliasing effects between regions of image elements having display values either side of the target range B of image values. The imaging may be two-dimensional or three-dimensional imaging. The morphological dilatation is preferably performed with a quasi-circular or a quasi-spherical structuring element having a radius of between two and three voxels.