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Algorithm 58 the above algorithm works for all regions

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Unformatted text preview: and 8connectivity. (algorithm 5.8) • • The above Algorithm works for all regions larger than one pixel. This algorithm is able to find region borders but does not find borders of region holes. To search for hole borders as well, the border must be traced starting in each region or hole border element if this element has never been a member of any border previously traced. • Note that if objects are of unit width, more conditions must be added. • The inner border is always part of a region but the outer border never is. Therefore, if two regions are adjacent, they never have a common border, which causes difficulties in higher processing levels with region description, region merging, etc. The inter-pixel boundary extracted, for instance, from crack edges is common to adjacent borders, nevertheless, its position cannot be specified in pixel co-ordinates. • Boundary properties better than those of outer borders may be found in extended borders. o single common border between adjacent regions o may be specified using standard pixel co-ordinates o the boundary shape is exactly equal to the inter-pixel shape but is shifted one halfpixel down and one half-pixel right The existence of a common border between regions makes it possible to incorporate into the boundary tracing a boundary description process. Faculty of Engineering Robotics Technology MECH 4041 15 B.Eng (Hons.) Mechatronics S. Venkannah Mechanical and Production Engineering Department A more sophisticated method for extended boundary tracing is based on detecting common boundary segments between adjacent regions and vertex points in boundary segment connections. The detection process is based on a look-up table, which defines all possible situations of the local configuration of 2*2 pixel windows, depending on the previous detected direction of boundary, and on the status of window pixels which can be inside or outside a region. Note that no hole-border tracing is included in the algorithm. The holes are considered separate regions and therefore the borders between the region and its hole are traced as a...
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