A Shape Recognition Method Based on Graph- and Line-Contexts

The shape, or contour, of an object is usually stable and persistent, so it is a good basis for invariant recognition. For this purpose, two problems must be addressed. The first is to obtain clean edges, and the second is to organize those edges into a structured data form upon which the necessary manipulations and analysis may be performed. Simple cells in the primary visual cortex are specialized in orientation detection, so the neural mechanism can be simulated by a computational model, which can produce a fairly clean set of lines, and all of them in vectors rather than in pixels. Then a line-context descriptor was designed to describe geometrical distribution of lines in a local area. All lines were also recorded by a weighted graph, and its minimum spanning tree can be used to describe the topological features of an object. An iterative matching algorithm was developed by combining line-context descriptors and minimum spanning tree, and was shown to match objects of the same type but with different shapes very well. Our results suggest that key to representation efficiency of searchable trees is to apply a mid-level line-context. This once more confirms the crucial role played by simple cells in visual processing path, for its preprocessing can greatly ease the subsequent processing.