bwperim (Image Processing Toolbox User's Guide)

Image Processing Toolbox User's Guide

Find perimeter pixels in binary image

Syntax

BW2 = bwperim(BW1)
BW2 = bwperim(BW1,CONN)

Description

BW2 = bwperim(BW1) returns a binary image containing only the perimeter pixels of objects in the input image BW1. A pixel is part of the perimeter if it is nonzero and it is connected to at least one zero-valued pixel. The default connectivity is 4 for two dimensions, 6 for three dimensions, and conndef(ndims(BW), 'minimal') for higher dimensions.

BW2 = bwperim(BW1,CONN) specifies the desired connectivity. CONN can 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

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 can 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.

Class Support

BW1 must be logical or numeric, and it must be nonsparse. BW2 is of class logical.

Example

BW1 = imread('circbw.tif');
BW2 = bwperim(BW1,8); 
imshow(BW1)
figure, imshow(BW2)

See Also

bwarea, bweuler, conndef, imfill

bwpack bwselect