imdilate

Dilate image

Syntax

J = imdilate(I,SE)

J = imdilate(I,nhood)

J = imdilate(___,packopt)

J = imdilate(___,shape)

Description

J = imdilate(I,SE) dilates the grayscale, binary, or packed binary image I using the structuring element SE.

J = imdilate(I,nhood) dilates the image I, where nhood is a matrix of 0s and 1s that specifies the structuring element neighborhood.

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

J = imdilate(___,packopt) specifies whether I is a packed binary image.

J = imdilate(___,shape) specifies the size of the output image.

Examples

Dilate Image with Vertical Line Structuring Element

Read a binary image into the workspace.

BW = imread('text.png');

Create a vertical line shaped structuring element.

se = strel('line',11,90);

Dilate the image with a vertical line structuring element and compare the results.

BW2 = imdilate(BW,se);
imshow(BW), title('Original')

figure, imshow(BW2), title('Dilated')

Dilate Grayscale Image with Rolling Ball

Read a grayscale image into the workspace.

originalI = imread('cameraman.tif');

Create a nonflat ball-shaped structuring element.

se = offsetstrel('ball',5,5);

Dilate the image.

dilatedI = imdilate(originalI,se);

Display the original image and the dilated image.

imshowpair(originalI,dilatedI,'montage')

Determine Domain of Composition of Structuring Elements

Create two flat, line-shaped structuring elements, one at 0 degrees and the other at 90 degrees.

se1 = strel('line',3,0)

se1 = 
strel is a line shaped structuring element with properties:

      Neighborhood: [1 1 1]
    Dimensionality: 2

se2 = strel('line',3,90)

se2 = 
strel is a line shaped structuring element with properties:

      Neighborhood: [3x1 logical]
    Dimensionality: 2

Dilate the scalar value 1 with both structuring elements in sequence, using the 'full' option.

composition = imdilate(1,[se1 se2],'full')

composition = 3×3

     1     1     1
     1     1     1
     1     1     1

Dilate Points in 3D Space Using Spherical Structuring Elements

Create a logical 3D volume with two points.

BW = false(100,100,100);
BW(25,25,25) = true;
BW(75,75,75) = true;

Dilate the 3D volume using a spherical structuring element.

se = strel('sphere',25);
dilatedBW = imdilate(BW,se);

Visualize the dilated image volume.

figure
isosurface(dilatedBW, 0.5)

Input Arguments

I — Input image

grayscale image | binary image | packed binary image

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

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

SE — Structuring element

strel object | offsetstrel object | array of strel objects | array of offsetstrel objects

Structuring element, specified as a scalar strel object or offsetstrel object. SE can also be an array of strel object or offsetstrel objects, in which case imdilate performs multiple dilations of the input image, using each structuring element in succession.

imdilate performs grayscale dilation for all images except images of data type logical. In this case, the structuring element must be flat and imdilate performs binary dilation.

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]

packopt — Indicator of packed binary image

'notpacked' (default) | 'packed'

Indicator of packed binary image, specified as one of the following.

Value	Description
'notpacked'	I is treated as a normal array.
'ispacked'	I is treated as a packed binary image as produced by bwpack. I must be a 2-D uint32 array and SE must be a flat 2-D structuring element. The value of shape must be 'same'.

Data Types: char | string

shape — Size of output image

'same' (default) | 'full'

Size of the output image, specified as one of the following.

Value	Description
'same'	The output image is the same size as the input image. If the value of packopt is 'ispacked', then shape must be 'same'.
'full'	Compute the full dilation.

Data Types: char | string

Output Arguments

J — Dilated image

grayscale image | binary image | packed binary image

Dilated image, returned as a grayscale image, binary image, or packed binary image. If the input image I is packed binary, then J is also packed binary. J has the same data type as I.

More About

Binary Dilation

The binary dilation of A by B, denoted A ⨁ B, is defined as the set operation:

$$A\oplus B=\left\{z|{\left(\widehat{B}\right)}_z\cap A\ne \varnothing \right\},$$

where $$\widehat{B}$$ is the reflection of the structuring element B. In other words, it is the set of pixel locations z, where the reflected structuring element overlaps with foreground pixels in A when translated to z. Note that some applications use a definition of dilation in which the structuring element is not reflected.

For more information about binary dilation, see [1].

Grayscale Dilation

In the general form of grayscale dilation, the structuring element has a height. The grayscale dilation of A(x, y) by B(x, y) is defined as:

$$\left(A\oplus B\right)\left(x,y\right)=\max \left\{A(x-x^{\prime },y-y^{\prime })+B(x^{\prime },y^{\prime })|\left(x^{\prime },y^{\prime }\right)\in D_B\right\},$$

where D_B is the domain of the structuring element B and A(x, y) is assumed to be –∞ outside the domain of the image. Note that some applications define grayscale dilation using an equation with A(x + x′, y + y′) instead of A(x – x′, y – y′).

To create a structuring element with nonzero height values, use the syntax strel(nhood,height), where height gives the height values and nhood corresponds to the structuring element domain, D_B.

Most commonly, grayscale dilation is performed with a flat structuring element (B(x,y) = 0). Grayscale dilation using such a structuring element is equivalent to a local-maximum operator:

$$\left(A\oplus B\right)\left(x,y\right)=\max \{A(x-x^{\prime },y-y^{\prime })|(x^{\prime },y^{\prime })\in D_B\}.$$

All of the strel syntaxes except for strel(nhood,height), strel('arbitrary',nhood,height), and strel('ball',___) produce flat structuring elements.

Tips

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

  You can use this behavior to perform morphological dilation 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, imdilate determines the center element of nhood by floor((size(nhood)+1)/2).

• imdilate automatically takes advantage of the decomposition of a structuring element object (if it exists). Also, when performing binary dilation with a structuring element object that has a decomposition, imdilate automatically uses binary image packing to speed up the dilation [3].

References

[1] Gonzalez, Rafael C., Richard E. Woods, and Steven L. Eddins. Digital Image Processing Using MATLAB. Third edition. Knoxville: Gatesmark Publishing, 2020.

[2] Haralick, Robert M., and Linda G. Shapiro. Computer and Robot Vision. 1st ed. USA: Addison-Wesley Longman Publishing Co., Inc., 1992, pp. 158-205.

[3] Boomgaard, Rein van den, and Richard van Balen. “Methods for Fast Morphological Image Transforms Using Bitmapped Binary Images.” CVGIP: Graphical Models and Image Processing 54, no. 3 (May 1, 1992): 252–58. https://doi.org/10.1016/1049-9652(92)90055-3.

Extended Capabilities

C/C++ Code Generation

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

Usage notes and limitations:

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

• The structuring element SE must be a single element—arrays of structuring elements are not supported. To obtain the same result as that obtained using an array of structuring elements, call the function sequentially.

• When the target is MATLAB Host Computer, the packopt and shape arguments must be compile-time constants. When the target is any other platform, the packopt syntax is not supported.

GPU Code Generation

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

Usage notes and limitations:

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

• Packed binary input images (packopt syntax) are not supported.

• For 3-D input images with more than three channels, only C/C++ code is generated.

• The structuring element SE must be a compile-time constant. CUDA^® code is generated only for 1-D or 2-D structuring elements. If the structuring element is 3-D, C/C++ code is generated. Code generation is not supported for structuring elements with more than three dimensions.

• For non-flat structuring elements, only C/C++ code is generated.

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.

• The packopt argument is not supported on the GPU.

For more information, see Image Processing on a GPU.