Dark and Bright Symmetry

As mentioned previously, cocircular edges need to be parallel or anti-parallel with the normals of the boundary of the annular sampling region to contribute to the symmetry. The resulting output will be referred to as ``general symmetry''. It is possible to restrict this definition further and perform the computations only on edges that are parallel to the normals of the sampling region; this yields ``dark symmetry'' and includes those edges which are oriented away from the center of cocircularity. Typically, dark symmetry will detect interest points and lines of symmetry in dark objects treating bright regions in the image as the background. ``Bright symmetry'', on the other hand, usually detects only bright objects by considering edges oriented towards the point of cocircularity.