imtophat

Top-hat filtering

Syntax

J = imtophat(I,SE)

J = imtophat(I,nhood)

Description

J = imtophat(I,SE) performs morphological top-hat filtering on the grayscale or binary image I using the structuring element SE. Top-hat filtering computes the morphological opening of the image (using imopen) and then subtracts the result from the original image.

J = imtophat(I,nhood) top-hat filters the image I, where nhood is a matrix of 0s and 1s that specifies the structuring element neighborhood.

This syntax is equivalent to imtophat(I,strel(nhood)).

Examples

Use Top-hat Filtering to Correct Uneven Illumination

This example shows how to use top-hat filtering with a disk-shaped structuring element to remove uneven background illumination from an image with a dark background.

Read an image and display it.

original = imread('rice.png');
imshow(original)

Create the structuring element.

se = strel('disk',12);

Perform the top-hat filtering and display the image.

tophatFiltered = imtophat(original,se);
figure
imshow(tophatFiltered)

Use imadjust to improve the visibility of the result.

contrastAdjusted = imadjust(tophatFiltered);
figure
imshow(contrastAdjusted)

Input Arguments

I — Input image

grayscale image | binary image

Input image, specified as a grayscale image or binary image of any dimension.

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

SE — Structuring element

strel object | offsetstrel object

Structuring element, specified as a single strel object or offsetstrel object. If the image I is data type logical, the structuring element must be flat.

nhood — Structuring element neighborhood

matrix of 0s and 1s

Structuring element neighborhood, specified as a matrix of 0s and 1s.

Example: [0 1 0; 1 1 1; 0 1 0]

Output Arguments

J — Top-hat filtered image

grayscale image | binary image

Top-hat filtered image, returned as a grayscale image or binary image. J has the same data type as input image I.

Tips

• If the dimensionality of the image I is greater than the dimensionality of the structuring element, then the imtophat function applies the same morphological opening to all planes along the higher dimensions.

  You can use this behavior to perform top-hat filtering on RGB images. Specify a 2-D structuring element for RGB images to operate on each color channel separately.

• When you specify a structuring element neighborhood, imtophat determines the center element of nhood by floor((size(nhood)+1)/2).

Extended Capabilities

C/C++ Code Generation

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

Usage notes and limitations:

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

• The input image I must be 2-D or 3-D.

GPU Code Generation

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

Usage notes and limitations:

• The image input I must be 2-D or 3-D.

• The structuring element SE must be a compile-time constant.

Thread-Based Environment

Run code in the background using MATLAB® backgroundPool or accelerate code with Parallel Computing Toolbox™ ThreadPool.

This function fully supports thread-based environments. For more information, see Run MATLAB Functions in Thread-Based Environment.

GPU Arrays

Accelerate code by running on a graphics processing unit (GPU) using Parallel Computing Toolbox™.

Usage notes and limitations:

• gpuArray input must be of type uint8 or logical.

• The structuring element SE must be flat and 2-D.

For more information, see Image Processing on a GPU.

Version History

Introduced before R2006a

R2022b: Support for thread-based environments

imtophat now supports thread-based environments.