Image Processing Toolbox

Eroding an Image

To erode an image, use the imerode function. The imerode function accepts two primary arguments:

• The input image to be processed (grayscale, binary, or packed binary image)
• A structuring element object, returned by the strel function, or a binary matrix defining the neighborhood of a structuring element

imerode also accepts three optional arguments: PADOPT, PACKOPT, and M.

The PADOPT argument affects the size of the output image. The PACKOPT argument identifies the input image as packed binary. If the image is packed binary, M identifies the number of rows in the original image. (See the bwpack reference page for more information about binary image packing.)

The following example erodes the binary image, circbw.tif:

1. Read the image into the MATLAB workspace.

• BW1 = imread('circbw.tif');
  

2. Create a structuring element. The following code creates a diagonal structuring element object. (For more information about using the strel function, see Structuring Elements.)

• SE = strel('arbitrary',eye(5));
  SE=
   
  Flat STREL object containing 5 neighbors.
  
  Neighborhood:
       1     0     0     0     0
       0     1     0     0     0
       0     0     1     0     0
       0     0     0     1     0
       0     0     0     0     1
  

3. Call the imerode function, passing the image, BW, and the structuring element, SE, as arguments.

• BW2 = imerode(BW1,SE);
  

1. Notice the diagonal streaks on the right side of the output image. These are due to the shape of the structuring element.

   • imshow(BW1)
     figure, imshow(BW2)
     
     
     

Figure 9-4: Circbw.tif Before and After Erosion with a Diagonal Structuring Element

Dilating an Image

Combining Dilation and Erosion