An apparatus for processing a raster image comprising a plurality of pixels is disclosed. The apparatus comprises a non-transitory computer readable medium for storing steps of a computer program, and a computer processor connected to the non-transitory computer readable medium for executing the steps of the computer program. A plurality of horizontal axial blobs are identified in the raster image, a plurality of vertical axial blobs are identified in the raster image, and the horizontal and vertical axial blobs are linked into a feature blob.