imhmax

Suppress regional maxima in image using H-maxima transform

Syntax

J = imhmax(I,H)

J = imhmax(I,H,conn)

Description

J = imhmax(I,H) suppresses regional maxima in the grayscale image I by using the H-maxima transform. The H-maxima transform decreases the height of all regional maxima by an amount up to H. As a result, the transform fully suppresses regional maxima whose height is less than H. Regional maxima are connected pixels with the same intensity value, t, that are surrounded by pixels with an intensity value less than t.

J = imhmax(I,H,conn) additionally specifies the connectivity value used to identify the regional maxima in I.

Examples

Calculate H-Maxima Transform

Create a sample 10-by-10 image. Add two regional maxima, each consisting of an area of connected pixels surrounded by lower intensity values.

a = 10*ones(10,10);
a(2:4,2:4) = 13;  
a(6:8,6:8) = 18;

This image is a grayscale representation of the pixel values. The height of each maximum depends on the surrounding pixel values.

Apply the H-maxima transform that decreases the height of regional maxima by up to 4.

b = imhmax(a,4);

This image is a grayscale representation of the transformed image. The transform fully suppresses one of the maxima. The transform partially suppresses the taller maximum, and subtracts 4 from the intensity values of the pixels in that maximum.

Find Brightest Intensity Peaks in Image Using H-Maxima Transform

You can suppress small regional maxima to identify the brightest peaks in an image.

Read a grayscale image of snowflakes into the workspace and display it.

I = imread("snowflakes.png");
imshow(I,InitialMagnification=200)

Find the regional maxima in the image.

regmax = imregionalmax(I);

Display a mask of the regional maxima pixels as an overlay on the original image. The regional maxima correspond to shallow intensity fluctuations, rather than the snowflakes.

overlay = imoverlay(I,regmax,"green");
imshow(overlay,InitialMagnification=200)

Apply the H-maxima transform to remove the shallow intensity peaks. Display the filtered image.

h = 75;
B = imhmax(I,h);
imshow(B,InitialMagnification=200)

Find the regional maxima of the filtered image. Display a mask of the maxima as an overlay on the original image.

regmaxfilt = imregionalmax(B);
overlayfilt = imoverlay(I,regmaxfilt,"green");
imshow(overlayfilt,InitialMagnification=200)

Note that you can alternatively use the imextendedmax function to apply the H-maxima transform and calculate the regional maxima in one step.

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 — H-maxima transform

nonnegative scalar

H-maxima transform, specified as a nonnegative scalar.

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, imhmax 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

J — Transformed image

numeric array

Transformed image, returned as a numeric array of the same size and data type 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:

• imhmax supports the generation of C code (requires MATLAB^® Coder™). Note that if you choose the generic MATLAB Host Computer target platform, imhmax 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™.

Usage notes and limitations:

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

Version History

Introduced before R2006a