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imregionalmax

Regional maxima

Description

example

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.

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

Examples

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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

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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

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

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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

Introduced before R2006a