In the last chapter we became acquainted with neighborhood operations. In fact, we only studied very simple structures in a local neighborhood, namely the edges. We concentrated on the detection of edges, but we did not consider how to determine their orientation. Orientation is a significant property not only of edges but also of any pattern that shows a preferred direction. The local orientation of a pattern is the property which leads the way to a description of more complex image features. Local orientation is also a key feature in motion analysis (chapter 17). Furthermore, there is a close relationship between orientation and projection (section 13.4.2).
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