Junctions are local gray-value structures with multiple intrinsic scales and orientations.
A signature characterizing such a junction can be only obtained by applying a filter in different scales and orientations. The response of a filter at an arbitrary scale and orientation can be approximated as a linear combination of a finite set of so-called basis filters. Although steerability provides us with a solid mathematical theory, the complexity of its implementation remains high. Due to the uncertainty principle the product of orientational resolution of a steerable filter and its orientational bandwidth has a lower bound. Therefore, in order to achieve a high orientational selectivity we have to apply a huge number of basis filters.