Documentation

imregionalmax

Regional maxima

Syntax

  • BW = imregionalmax(I) example
  • BW = imregionalmax(I,conn)
  • gpuarrayBW = imregionalmax(gpuarrayI,___)

Description

example

BW = imregionalmax(I) returns the binary image BW that identifies the regional maxima in I. Regional maxima are connected components of pixels with a constant intensity value, and whose external boundary pixels all have a lower value. In BW, pixels that are set to 1 identify regional maxima; all other pixels are set to 0. By default, imregionalmax uses 8-connected neighborhoods for 2-D images and 26-connected neighborhoods for 3-D images. For higher dimensions, imregionalmax uses conndef(ndims(I)),'maximal').

This function supports code generation (see Tips).

BW = imregionalmax(I,conn) computes the regional maxima, where conn specifies the connectivity.

gpuarrayBW = imregionalmax(gpuarrayI,___) performs the operation on a GPU. The input image must be a gpuArray. The function returns a gpuArray. This syntax requires Parallel Computing Toolbox™.

Examples

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Find Regional Maxima in Simple Sample Image

Create a 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    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.

regmax = imregionalmax(A)
regmax =
     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

Find Regional Minima in Simple Sample Image on a GPU

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

A = 10*gpuArray.ones(10,10);
A(2:4,2:4) = 22;    % maxima 12 higher than surrounding pixels
A(6:8,6:8) = 33;    % maxima 23 higher than surrounding pixels
A(2,7) = 44;
A(3,8) = 45;
A(4,9) = 44
A =

    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

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 0.

regmax = imregionalmax(A)
regmax =

     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

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I — Input imagenonsparse numeric array of any dimension

Input array, specified as a nonsparse numeric array of any dimension.

Example: I = imread(‘glass.png'); BW = imregionalmax(I);

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

conn — Connectivity8 (default) | 4 | 6 | 18 | 26 | 3-by-3-by- ...-by-3 matrix of zeroes and ones

Connectivity, specified as a one of the scalar values in the following table. By default, imregionalmax uses 8-connected neighborhoods for 2-D images and 26-connected neighborhoods for 3-D images. For higher dimensions, imregionalmax uses conndef(ndims(I)),'maximal'). 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 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.

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

Example: regmax = imregionalmax(A,4);

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

gpuarrayI — Input image for GPUgpuArray

Input image for GPU, specified as a gpuArray.

Example: gpuarrayI = gpuArray(imread('cameraman.tif')); gpuarrayBW = imregionalmax(gpuarrayI);

Output Arguments

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BW — Transformed imagelogical array

Transformed image, returned as a logical array the same size as I.

gpuarrayBW — Transformed imagegpuArray

Transformed image, returned as a gpuArray.

More About

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Tips

  • This function supports the generation of C code using MATLAB® Coder™. Note that if you choose the generic MATLAB Host Computer target platform, the function 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 Understanding Code Generation with Image Processing Toolbox.

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

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