A sequential method of extracting contour chains from an image

An efficient sequential method of tracing contour chains around foreground objects in an image is presented. The image is scanned row by row, extracting the run lengths of each row, determining their connectivity with runs in the preceding row, and incrementally building up contour chains accordingly. The contours are stored in a new list structure that reflects their topological nesting in the image. The organization of this list provides a greater degree of topological information than is provided by other methods.