Extracting Boundary Pixels from a Segmented Image after segmentation connected components region boundary may be extracted border algorithm to extract all region boundaries in left right top bottom Concepts and Data Structures

Introduction edge detection labels each pixel as edge or no edge additional properties of edge direction gradient magnitude contrast edge grouping edge pixels in same region boundary grouped together edge detector typically produces short linear disjointed edge segments each edge segment has an orientation and a position edge segments of little use until aggregated into extended edges global edge aggregation upon proximity relative orientation contrast local edge aggregation extends edges by seeking compatible neighbor edges global methods can incorporate domain knowledge into cost functions global methods more robust to noisy edge data global methods bought at expense of relatively high computational cost aggregation into extended edges and parametric description new research area extended edges like other curves can be described at multiple scales Fig a image of an industrial part Fig b edges of a large dot edge center medium dot edge extension Fig c thinning of b leads to the minimally connected graph Fig d simple contour following based on orientation compatibility Fig e polygonal approximation with vertices highlighted Fig f tangent versus arc length plot Fig g same as d except letters indicating initial knots Fig h tted straight lines and conics and nal set of knots Nalwa A Guided Tour of Computer Vision Fig