关键词: 边界跟踪, 链码, 边点梯度方向, 边段提取, 断点, 岔路

Abstract: The extracting of boundary contour is the base of studying the shape characteristics.It has a major impact on the high level of image processing such as image characteristic description，identification and understanding.However，due to the effects of noise，light and many other reasons，the edge image obtained after pretreated often occurs the originally connected boundaries partial rupture.The traditional boundary tracing algorithm can not cross the breakpoints to continue tracing.In addition，when the branch occurs in the tracing process，the traditional boundary tracing algorithm，only to trace the first searched boundary point，can not control the right direction of boundary tracing.This paper presents a smooth curve segment extracting method guided by the gradient direction of boundary point，which not only can cross the breakpoint to continue tracing，but also can effectively reduce the wrong choice of the branch，while still meeting the requirement of a smooth edge segment.

Key words: boundary tracing, chain code, the gradient direction of boundary point, curve segment extracting, breakpoint, branch