Certain imaging systems, such as automatic explosives detection systems, employ techniques that utilize image processing, feature extraction and decision making steps to detect threats in images. Such techniques use segmentation as a first algorithmic step, which extracts data representing objects from image data. Some of the extracted objects are actually composed of multiple distinct physical objects. For these compound objects discrimination becomes difficult because computed object properties are less specific than properties computed for a single physical object. A technique is described which includes splitting such compound objects by separating the data of each component from the rest of the data and using properties of density histograms based on voxel distributions in both density and spatial domains.