imextendedmin

Extended-minima transform

Syntax

BW = imextendedmin(I,H)

BW = imextendedmin(I,H,conn)

Description

BW = imextendedmin(I,H) computes the extended-minima transform for the image I, which is the regional minima of the H-minima transform.

• Regional minima are connected components of pixels with a constant intensity value, and whose external boundary pixels all have a higher value. The H-minima transform suppresses all regional minima with a depth less than or equal to H.

• The extended-minima transform, which is the regional minima of the H-minima transform, identifies regional minima with a depth greater than H.

Use the extended-minima transform to detect dark regions in an image while ignoring small intensity variations.

BW = imextendedmin(I,H,conn) specifies the pixel connectivity conn to use to identify the connected components in the regional minima.

Examples

Perform Extended-Minima Transform

Read an image into the workspace.

I = imread("threads.png");

Visualize the image. Observe that the threads in the image represent regions that are significantly darker than their surroundings.

figure
imshow(I)

Calculate the extended-minima transform with a low value for H, the value that indicates the minimum depth of regional minima.

H = 1;
BWlow = imextendedmin(I,H);

Visualize the transformed image. Observe that the transform detects insignificant variations because the specified minimum depth of regional minima is low.

figure
imshow(BWlow)

Calculate the extended-minima transform with a high value for H.

H = 20;
BWhigh = imextendedmin(I,H);

Visualize the transformed image. Observe that the transform ignores small intensity variations and detects entire regions that are significantly darker than their surroundings because the specified minimum depth of regional minima is high.

figure
imshow(BWhigh)

Input Arguments

I — Input image

numeric array

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

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

H — Minimum depth of regional minima

nonnegative scalar

Minimum depth of regional minima, specified as a nonnegative scalar. Specify a large value for H to identify only those regions in the image that are significantly darker than their surroundings.

Example: 80

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

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, imextendedmin 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 — Transformed image

logical array

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

References

[1] Soille, P. Morphological Image Analysis: Principles and Applications. Springer-Verlag, 1999, pp. 170-171.

Extended Capabilities

C/C++ Code Generation

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

Usage notes and limitations:

• imextendedmin supports the generation of C code (requires MATLAB^® Coder™). Note that if you choose the generic MATLAB Host Computer target platform, imextendedmin 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 third input argument, conn, must be a compile-time constant.

GPU Code Generation

Generate CUDA® code for NVIDIA® GPUs using GPU Coder™.

Refer to the usage notes and limitations in the C/C++ Code Generation section. The same usage notes and limitations apply to GPU code generation.

Version History

Introduced before R2006a