Multiple desired objects within a three-dimensional tomographic data set which occupy the same portion of the image histogram with other unwanted objects are separated with reduced reliance on user interaction by applying connectivity to the unwanted objects and setting the voxels to a new value which removes them from the portion of the histogram. Unwanted objects can be identified by examination of the original two-dimensional slices or after examination of a three-dimensional image to excise objects, whereby the invention functions as an electronic scalpel.