Steve on Image Processing and MATLAB

Concepts, algorithms & MATLAB

Moving the origin of a structuring element

A customer contacted Tech Support recently to ask the following question about structuring elements and dilation:

If I created a structuring element from the matrix [1 1; 1 1], then the origin of the structuring element is the (1,1) or upper-left element. How do I create a structuring element so that the origin is at (1,2) or (2,1)?

There are two equivalent ways to accomplish this.

In the first way, you add a row or column (or both) to the matrix that you pass to strel or imdilate so that the center of the new matrix is the desired structuring element origin. For example:

se = strel([0 1 1; 0 1 1; 0 0 0])
 
se =
 
Flat STREL object containing 4 neighbors.

Neighborhood:
     0     1     1
     0     1     1
     0     0     0

 

In the second way, you pass the original 2-by-2 matrix to strel and then call the function translate to "move" the origin to the desired location.

se = strel([1 1; 1 1])
 
se =
 
Flat STREL object containing 4 neighbors.

Neighborhood:
     1     1
     1     1

 
se2 = translate(se,[-1 0])
 
se2 =
 
Flat STREL object containing 4 neighbors.

Neighborhood:
     0     1     1
     0     1     1
     0     0     0

 




Published with MATLAB® R2015a

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