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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