imregionalmin (Image Processing Toolbox User's Guide)

Image Processing Toolbox User's Guide

Find regional minima

Syntax

BW = imregionalmin(I)
BW = imregionalmin(I,CONN)

Description

BW = imregionalmin(I) computes the regional minima of I. The output binary image BW has value 1 corresponding to the pixels of I that belong to regional minima and 0 otherwise. BW is the same size as I.

Regional minima are connected components of pixels with a constant intensity value, and whose external boundary pixels all have a higher value.

By default, imregionalmin uses 8-connected neighborhoods for 2-D images and 26-connected neighborhoods for 3-D images. For higher dimensions, imregionalmin uses conndef(ndims(I),'maximal').

BW = imregionalmin(I,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 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

I can be any nonsparse, numeric class and any dimension. BW is logical.

Example

Create a 10-by-10 pixel sample image that contains two regional minima.

A = 10*ones(10,10);
A(2:4,2:4) = 2; 
A(6:8,6:8) = 7; 
A =
    10    10    10    10    10    10    10    10    10    10
    10     2     2     2    10    10    10    10    10    10
    10     2     2     2    10    10    10    10    10    10
    10     2     2     2    10    10    10    10    10    10
    10    10    10    10    10    10    10    10    10    10
    10    10    10    10    10     7     7     7    10    10
    10    10    10    10    10     7     7     7    10    10
    10    10    10    10    10     7     7     7    10    10
    10    10    10    10    10    10    10    10    10    10
    10    10    10    10    10    10    10    10    10    10

Pass the sample image A to imregionalmin. The function returns a binary image, the same size as A, in which pixels with the value 1 represent the regional minima in A. imregionalmin sets all other pixels in to zero (0).

B = imregionalmin(A)
B = 
     0     0     0     0     0     0     0     0     0     0
     0     1     1     1     0     0     0     0     0     0
     0     1     1     1     0     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     1     1     1     0     0
     0     0     0     0     0     1     1     1     0     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

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