
level, then we choose the middle one. If the two nonadjacent points share the
highest gray level, we choose arbitrarily.
With the assumption of a noise-free image of a monotone spot, this algorithm
will trace out the maximum gradient boundary nicely. However, if noise is present,
the tracking is likely to go away from the boundary. Noise effects can be reduced
by smoothing the gradient image before tracking or by implementing a tracking
bug, which works as follows. First a rectangular averaging window, usually having
uniform weights, is defined to embody the bug (Fig. 9.13b). The last two or last few
boundary points define the current boundary direct ...