5.Image_segmentation

# A weak edge positioned between two strong edges

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Unformatted text preview: or decreased. A weak edge positioned between two strong edges provides an example of context; it is highly probable that this inter-positioned weak edge should be a part of a resulting boundary. If, on the other hand, an edge (even a strong one) is positioned by itself with no supporting context, it is probably not a part of any border. • The method discussed here uses crack edges (edges located between pixels). Edge context is considered at both ends of an edge, giving the minimal edge neighborhood. All three possible edge positions at the end of the edge e must be included to cover all the possible ways the border can continue from both ends of e. Furthermore, two edge positions parallel with the edge e can be included in the local neighborhood- these parallel positions compete with the edge e in the placement of the border. Edge relaxation aims for continuous border construction. The central edge e has a vertex at each of its ends, and three possible border continuations can be found from both of these vertices. • Vertex type -- number of edges emanating from the vertex, not counting the edge e. Faculty of Engineering Robotics Technology MECH 4041 14 B.Eng (Hons.) Mechatronics S. Venkannah • Mechanical and Production Engineering Department The type of edge e can then be represented using a number pair i-j describing edge patterns at each vertex, where i and j are the vertex types of the edge e. By symmetry only the cases where i ≤ j need be considered. Edge relaxation is an iterative method, with edge confidences converging either to zero (edge termination) or one (the edge forms a border). Border tracing If a region border is not known but regions have been defined in the image, borders can be uniquely detected. First, let us assume that the image with regions is either binary or that regions have been labeled. The first goal is to determine inner region borders. • An inner region border is a subset of the region • An outer border is not a subset of the region. • The following algorithm covers inner boundary tracing in both 4-connectivity...
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