11.Representation and Description

11.1 Representation

11.1.1 Boundary (Border) Following -Its output is an ordered sequence of points

11.1.2 Chain Codes -Chain codes are used to represent a boundary by a connected sequence of straight-line segments of specified length and direction

11.1.3 Polygonal Approximations Using Minimum-Perimeter Polygons -For a closed boundary, the approximation becomes exact when the number of segments of the polygon is equal to the number of points in the boundary so that each pair of adjacent points defines a segment of the polygon

11.1.4 Other Polygonal Approximation Approaches -Merging technique -Splitting techniques

11.1.5 Signatures -A signature is a 1-D functional representation of a boundary and maybe generated in various ways.

11.1.6 Boundary Segments - This approach is particularly attractive when the boundary contains one or more significant concavities that carry shape information.

11.2 Boundary Descriptors

11.2.1 Some Simple Descriptors -These descriptors must be used with are because their interpretation depends on the length of the individual segments relative to the overall length of the boundary

11.2.2 Shape Numbers -The shape number of such a boundary is defined as the first difference of smallest magnitude

11.2.3 Fourier Descriptors -A Few Fourier descriptors can be used to capture the gross essence of a boundary

11.2.4 Statistical Moments -The shape of boundary segments can be described quantitatively by using statistical moments,such as the mean,variance, and higherorder moments

11.3 Regional Descriptors

11.3.1 Some Simple Descriptors -The area of a region is defined as the number of pixels in the region -The perimeter of a region is the length of its boundary.

11.3.2 Topological Descriptors -Topological properties are useful for global descriptions of regions in the image plane.

11.3.3 Texture -Statistical approaches -Structural approaches -Spectral approaches

11.4 Use of Principal Components for description

-It can treat the vectors as random quantities, just like we did when constructing an intensity histogram

11.5 Relational Descriptors

-The most obvious property of the coded structure is the repetitiveness of the elements a and b

-A simple description approach is to formulate a recursive relationship involving these primitive elements