imbothat

Bottom-hat filtering

Syntax

J = imbothat(I,SE)

J = imbothat(I,nhood)

Description

J = imbothat(I,SE) performs morphological bottom-hat filtering on the grayscale or binary image I using the structuring element SE. Bottom-hat filtering computes the morphological closing of the image (using imclose) and then subtracts the original image from the result.

J = imbothat(I,nhood) bottom-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 imbothat(I,strel(nhood)).

Examples

Enhance Contrast Using Bottom-hat and Top-hat Filtering

Read image into the workspace and display it.

I = imread('pout.tif');
imshow(I)

Create a disk-shaped structuring element.

se = strel('disk',3);

Add the original image I to the top-hat filtered image, and then subtract the bottom-hat filtered image.

J = imsubtract(imadd(I,imtophat(I,se)),imbothat(I,se));
figure
imshow(J)

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 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 — Bottom-hat filtered image

grayscale image | binary image

Bottom-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 imbothat function applies the same morphological closing to all planes along the higher dimensions.

  You can use this behavior to perform bottom-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, imbothat 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:

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

• To generate optimized C code, all input arguments except the input image I must be compile-time constants.

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.

• To generate optimized CUDA code, all input arguments except the input image I must be compile-time constants.

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

imbothat now supports thread-based environments.