imregionalmin

Regional minima

Syntax

BW = imregionalmin(I)

BW = imregionalmin(I,conn)

Description

BW = imregionalmin(I) returns the binary image BW that identifies the regional minima in grayscale image I. Regional minima are connected components of pixels with a constant intensity value, surrounded by pixels with a higher value.

BW = imregionalmin(I,conn) specifies the desired connectivity, conn.

Examples

Find Regional Minima in Simple Sample Image

Create a simple sample array with several regional minima.

A = 10*ones(10,10);
A(2:4,2:4) = 3;       
A(6:8,6:8) = 8

A = 10×10

    10    10    10    10    10    10    10    10    10    10
    10     3     3     3    10    10    10    10    10    10
    10     3     3     3    10    10    10    10    10    10
    10     3     3     3    10    10    10    10    10    10
    10    10    10    10    10    10    10    10    10    10
    10    10    10    10    10     8     8     8    10    10
    10    10    10    10    10     8     8     8    10    10
    10    10    10    10    10     8     8     8    10    10
    10    10    10    10    10    10    10    10    10    10
    10    10    10    10    10    10    10    10    10    10

Calculate the regional minima. The function returns a binary image, the same size as the input image, in which pixels with the value 1 represent the regional minima. imregionalmin sets all other pixels in to 0.

regmin = imregionalmin(A)

regmin = 10x10 logical array

   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

Input Arguments

I — Grayscale image

numeric array

Grayscale image, specified as a numeric array of any dimension.

Example: I = imread('cameraman.tif');

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

conn — Pixel connectivity

4 | 8 | 6 | 18 | 26 | 3-by-3-by- ... -by-3 matrix of 0s and 1s

Pixel connectivity, specified as one of the values in this table. The default connectivity is 8 for 2-D images, and 26 for 3-D images.

Value	Meaning
Two-Dimensional Connectivities
4	Pixels are connected if their edges touch. The neighborhood of a pixel are the adjacent pixels in the horizontal or vertical direction.	Current pixel is shown in gray.
8	Pixels are connected if their edges or corners touch. The neighborhood of a pixel are the adjacent pixels in the horizontal, vertical, or diagonal direction.	Current pixel is shown in gray.
Three-Dimensional Connectivities
6	Pixels are connected if their faces touch. The neighborhood of a pixel are the adjacent pixels in: One of these directions: in, out, left, right, up, and down	Current pixel is shown in gray.
18	Pixels are connected if their faces or edges touch. The neighborhood of a pixel are the adjacent pixels in: One of these directions: in, out, left, right, up, and down A combination of two directions, such as right-down or in-up	Current pixel is center of cube.
26	Pixels are connected if their faces, edges, or corners touch. The neighborhood of a pixel are the adjacent pixels in: One of these directions: in, out, left, right, up, and down A combination of two directions, such as right-down or in-up A combination of three directions, such as in-right-up or in-left-down	Current pixel is center of cube.

For higher dimensions, imregionalmin uses the default value conndef(ndims(I),'maximal').

Connectivity can also be defined in a more general way for any dimension by specifying a 3-by-3-by- ... -by-3 matrix of 0s and 1s. The 1-valued elements define neighborhood locations relative to the center element of conn. Note that conn must be symmetric about its center element. See Specifying Custom Connectivities for more information.

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

Output Arguments

BW — Locations of regional minima

logical array

Locations of regional minima, returned as a logical array of the same size as I. Pixels with the value 1 indicate regional maxima; all other pixels are set to 0.

Data Types: logical

Extended Capabilities

C/C++ Code Generation

Generate C and C++ code using MATLAB® Coder™.

Usage notes and limitations:

• imregionalmin supports the generation of C code (requires MATLAB^® Coder™). Note that if you choose the generic MATLAB Host Computer target platform, imregionalmin generates code that uses a precompiled, platform-specific shared library. Use of a shared library preserves performance optimizations but limits the target platforms for which code can be generated. For more information, see Types of Code Generation Support in Image Processing Toolbox.

• When generating code, the optional second input argument, conn, must be a compile-time constant.

Thread-Based Environment

Run code in the background using MATLAB® backgroundPool or accelerate code with Parallel Computing Toolbox™ ThreadPool.

This function fully supports thread-based environments. For more information, see Run MATLAB Functions in Thread-Based Environment.

GPU Arrays

Accelerate code by running on a graphics processing unit (GPU) using Parallel Computing Toolbox™.

Usage notes and limitations:

• Inputs must be 2-D, supporting only the 2-D connectivities (4 and 8).

For more information, see Image Processing on a GPU.

Version History

Introduced before R2006a

R2022b: Support for thread-based environments

imregionalmin now supports thread-based environments.