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Find perimeter of objects in binary image


BW2 = bwperim(BW)
BW2 = bwperim(BW,conn)



BW2 = bwperim(BW) returns a binary image that contains only the perimeter pixels of objects in the input image BW. 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. If you do not specify a return value, bwperim displays the result in a figure window.

BW2 = bwperim(BW,conn) where conn specifies the desired connectivity.


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Read binary image into workspace.

BW = imread('circles.png');

Calculate the perimeters of objects in the image.

BW2 = bwperim(BW,8);

Display the original image and the perimeters side-by-side.


Input Arguments

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Input binary image, specified as a logical or numeric matrix that must be 2-D, real, and nonsparse.

Example: BW = imread('circles.png'); BW2 = bwperim(BW);

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | logical

Connectivity, specified as one of the values in this table or a 3-by-3-by-...-by-3 array of 0s and 1s. The 1-valued elements define neighborhood locations relative to the center element of conn. Note that conn must be symmetric around its center element.



Two-dimensional connectivities


4-connected neighborhood


8-connected neighborhood

Three-dimensional connectivities


6-connected neighborhood


18-connected neighborhood


26-connected neighborhood

Example: BW2 = bwperim(BW,8);

Data Types: double | logical

Output Arguments

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Output image containing only perimeter pixels of objects, returned as a logical array.

Extended Capabilities

Introduced before R2006a

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