A method for segmenting a first object from a bounding object within a digital image identifies pixels between first and second endpoint pixels. A volume of interest is defined spanning at least a portion of the object. Pixels within the volume of interest are partitioned into a first subset of pixels that are neither the first object nor bounding object pixels and second subset of pixels that are not contained in the first subset. A spatially varying two-phase segmentation process segments the first object from the bounding object within the second subset of pixels according to the location of each subject pixel within the second subset relative to pixels in the first subset of pixels. The first object segmentation is refined according to the subject pixel location relative to the segmented bounding object and to the first subset of pixels. A segmented image is formed according to the refined segmentation.