Image Processing Toolbox

imclearborder

Suppress light structures connected to image border

Syntax

• IM2 = imclearborder(IM)
  IM2 = imclearborder(IM,CONN)
  

Description

IM2 = imclearborder(IM) suppresses structures that are lighter than their surroundings and that are connected to the image border. IM can be an intensity or binary image. The output image, IM2, is intensity or binary, respectively. The default connectivity is 8 for two dimensions, 26 for three dimensions, and conndef(ndims(BW),'maximal') for higher dimensions.

Note    For intensity images, imclearborder tends to reduce the overall intensity level in addition to suppressing border structures.

IM2 = imclearborder(IM,CONN) specifies the desired connectivity. CONN may have any of the following scalar values.

Value	Meaning
Two-dimensional connectivities
4	4-connected neighborhood
8	8-connected neighborhood
Three-dimensional connectivities
6	6-connected neighborhood
18	18-connected neighborhood
26	26-connected neighborhood

Connectivity may also be defined in a more general way for any dimension by using for CONN a 3-by-3-by- ... -by-3 matrix of 0's and 1's. The 1-valued elements define neighborhood locations relative to the center element of CONN. Note that CONN must be symmetric about its center element.

Note    A pixel on the edge of the input image might not be considered to be a "border" pixel if a nondefault connectivity is specified. For example, if conn = [0 0 0; 1 1 1; 0 0 0], elements on the first and last row are not considered to be border pixels because, according to that connectivity definition, they are not connected to the region outside of the image.

Class Support

IM can be a numeric or logical array of any dimension, and it must be nonsparse and real. IM2 has the same class as IM.

Example

The following examples use this simple binary image to illustrate the effect of of imclearborder when you specify different connectivities.

• BW =
       0     0     0     0     0     0     0     0     0
       0     0     0     0     0     0     0     0     0
       0     0     0     0     0     0     0     0     0
       1     0     0     1     1     1     0     0     0
       0     1     0     1     1     1     0     0     0
       0     0     0     1     1     1     0     0     0
       0     0     0     0     0     0     0     0     0
       0     0     0     0     0     0     0     0     0
       0     0     0     0     0     0     0     0     0
  

Using a 4-connected neighborhood, the pixel at (5,2) is not considered connected to the border pixel (4,1), so it is not cleared.

• BWc1 = imclearborder(BW,4)
  BWc1 =
       0     0     0     0     0     0     0     0     0
       0     0     0     0     0     0     0     0     0
       0     0     0     0     0     0     0     0     0
       0     0     0     1     1     1     0     0     0
       0     1     0     1     1     1     0     0     0
       0     0     0     1     1     1     0     0     0
       0     0     0     0     0     0     0     0     0
       0     0     0     0     0     0     0     0     0
       0     0     0     0     0     0     0     0     0
  

Using an 8-connected neighborhood, pixel (5,2) is considered connected to pixel (4,1) so both are cleared.

• BWc2 = imclearborder(BW,8)
  
  BWc2 =
  
       0     0     0     0     0     0     0     0     0
       0     0     0     0     0     0     0     0     0
       0     0     0     0     0     0     0     0     0
       0     0     0     1     1     1     0     0     0
       0     0     0     1     1     1     0     0     0
       0     0     0     1     1     1     0     0     0
       0     0     0     0     0     0     0     0     0
       0     0     0     0     0     0     0     0     0
       0     0     0     0     0     0     0     0     0
  

Algorithm

imclearborder uses morphological reconstruction where:

• the mask image is the input image
• the marker image is zero everywhere except along the border, where it equals the mask image

See Also

conndef

Reference

[1]  P. Soille, Morphological Image Analysis: Principles and Applications, Springer, 1999, pp. 164-165.

imbothat

imclose