imregionalmax

Regional maxima

Syntax

BW = imregionalmax(I)

BW = imregionalmax(I,conn)

Description

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

You optionally can identify regional maxima of 2-D images using a GPU (requires Parallel Computing Toolbox™).

BW = imregionalmax(I,conn) specifies the pixel connectivity, conn.

Examples

Find Regional Maxima in Simple Sample Image

Create a simple sample image with several regional maxima.

A = 10*ones(10,10);
A(2:4,2:4) = 22; 
A(6:8,6:8) = 33; 
A(2,7) = 44;
A(3,8) = 45;
A(4,9) = 44

A = 10×10

    10    10    10    10    10    10    10    10    10    10
    10    22    22    22    10    10    44    10    10    10
    10    22    22    22    10    10    10    45    10    10
    10    22    22    22    10    10    10    10    44    10
    10    10    10    10    10    10    10    10    10    10
    10    10    10    10    10    33    33    33    10    10
    10    10    10    10    10    33    33    33    10    10
    10    10    10    10    10    33    33    33    10    10
    10    10    10    10    10    10    10    10    10    10
    10    10    10    10    10    10    10    10    10    10

Find the regional maxima. Note that the result includes the regional maxima at (3,8).

regmax = imregionalmax(A)

regmax = 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   1   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

Input array, 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-connected	Pixels are connected if their edges touch. The neighborhood of a pixel are the adjacent pixels in the horizontal or vertical direction.
8-connected	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.
Three-Dimensional Connectivities
6-connected	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
18-connected	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
26-connected	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

For higher dimensions, imregionalmax 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 maxima

logical array

Locations of regional maxima, 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:

• imregionalmax supports the generation of C code (requires MATLAB^® Coder™). Note that if you choose the generic MATLAB Host Computer target platform, imregionalmax 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 Code Generation Using a Shared Library.

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

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.