Image Processing Toolbox    
ordfilt2

Perform two-dimensional order-statistic filtering

Syntax

Description

B = ordfilt2(A,order,domain) replaces each element in A by the order-th element in the sorted set of neighbors specified by the nonzero elements in domain.

B = ordfilt2(A,order,domain,S), where S is the same size as domain, uses the values of S corresponding to the nonzero values of domain as additive offsets.

B = ordfilt2(...,padopt) controls how the matrix boundaries are padded. Set padopt to 'zeros' (the default), or 'symmetric'. If padopt is 'zeros', A is padded with zeros at the boundaries. If padopt is 'symmetric', A is symmetrically extended at the boundaries.

Class Support

A can be of class uint8, uint16, or double. The class of B is the same as the class of A, unless the additive offset form of ordfilt2 is used, in which case the class of B is double.

Remarks

domain is equivalent to the structuring element used for binary image operations. It is a matrix containing only 1's and 0's; the 1's define the neighborhood for the filtering operation.

For example, B = ordfilt2(A,5,ones(3,3)) implements a 3-by-3 median
filter; B = ordfilt2(A,1,ones(3,3)) implements a 3-by-3 minimum filter;
and B = ordfilt2(A,9,ones(3,3)) implements a 3-by-3 maximum filter.
B = ordfilt2(A,1,[0 1 0; 1 0 1; 0 1 0]) replaces each element in A by the minimum of its north, east, south, and west neighbors.

The syntax that includes S (the matrix of additive offsets) can be used to implement grayscale morphological operations, including grayscale dilation and erosion.

See Also

medfilt2

Reference

Haralick, Robert M., and Linda G. Shapiro. Computer and Robot Vision, Volume I. Addison-Wesley, 1992.


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