Artificial Intelligence and Soft Computing: Behavioral ... - Arteimi.info

It may be noted that segmenting an image into regions without any
knowledge of the scene or its modules is practically infeasible. Generally, the
partial knowledge about the image such as an outdoor scene or a classroom or
a football tournament helps the segmentation process.
17.3.2 Labeling an Image
After segmenting an image into disjoint regions their shapes, spatial
relationships and other characteristics can be described and labeled for
subsequent interpretation. Typically a region description includes size of the
area, location of the center of mass, minimum bounding rectangles, boundary
contrast, shape classification number, chain code [6], position and type of
vertices and the like. We here explain the method for describing the boundary
of a region by a chain code.
A chain code is a sequence of integers, corresponding to direction of
traversal of the segments around a region, starting from a fixed position. The
direction of traversals of a segment is compared with the set of primitive
directions and the nearest one is selected. The traversed segment is encoded
following the standard integer code of that direction. The traversal is
continued until the chain repeats. The minimum index in the closed chain is
identified to match it with known strings, constructed in the same manner.
One important point that needs mention is that the consecutive chain
indices may be identical, when we move along a large linear segment. Under
this circumstance the portion of the chain describing the same index is
replaced by the index, taken only once. Constructing a chain code for the
boundary of a region is illustrated below (vide fig. 17.6 and 17.7).
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Fig. 17.6: The direction indices for chain coding: the angle between
two consecutive directions is 45 degrees.
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