1. A boundary determination system for determining boundaries of features in a digital image, said boundary determination system comprising a processor coupled to a memory, said processor is configured to: receive a selection of an area in a digital image; perform a principal component analysis on spectral signatures of pixels in the selected area in the digital image, including determining a centroid representing an average spectral signature and at least one ellipsoid representing a variance in the spectral signatures; generate a boundary around the selected area based on the principal component analysis; identify additional pixels outside the boundary to include within the boundary based on determining that additional spectral signatures of the additional pixels fall within the at least one ellipsoid; identify an inflection point in an amount of pixels covered by dilation of the boundary; and dilate the boundary to include at least a subset of the additional pixels without exceeding the inflection point.