Image Erosion without using MATLAB function 'imerode'

In MATLAB, ‘imerode’ is a function used to make the objects thin. MATLAB code without using 'imerode' function and explanation is provided here.

MATLAB CODE:

A=[1 0 1 1 1; 1 0 1 0 0; 1 1 1 0 0;0 0 1 1 1];

%Structuring element

B=[1 1 0];

%Pad array with ones on both sides

C=padarray(A,[0 1],1);

%Intialize the matrix D of size A with zeros

D=false(size(A));

for i=1:size(C,1)

    for j=1:size(C,2)-2

        In=C(i,j:j+2);

        %Find the position of ones in the structuring element

        In1=find(B==1);

        %Check whether the elements in the window have the value one in the

        %same positions of the structuring element

        if(In(In1)==1)

        D(i,j)=1;

        end

    end

end

display(D);

Explanation:

1.     Consider a matrix A and a structuring element B.

2.     Initialize a matrix D of size A with zeros.

3.     Construct a window of size B with the elements of matrix A.

4.     Check whether the ones in the structuring element B overlap the ones in the window.

5.     If it overlaps, then update D with one else zero.

Example 2:

A=imread('circles.png');

figure,imshow(A);

Original Image

%Structuring element

B=getnhood(strel('disk',11));

m=size(B,1);

%Pad array on all the sides

n=floor(m/2);

C=padarray(A,[n n],1);

%Intialize a matrix with size of matrix A

D=false(size(A));

for i=1:size(C,1)-(m-1)

    for j=1:size(C,2)-(m-1)

       

        In=C(i:i+(m-1),j:j+(m-1));

        In1=find(B==1);

        if(In(In1)==1)

        D(i,j)=1;

        end

       

    end

end

figure,imshow(D);

After Erosion

  

Image Dilation without using 'imdilate' function

           In MATLAB, ‘imdilate’is the function that dilates the image using a structuring element. Let’s learn how this function works using some examples and codes.

MATLAB CODE:

Example 1:

A=[1 0 0 0 1; 1 0 1 0 0; 1 1 1 0 0;0 0 1 1 1];

%Structuring element

B=[1 0 0; 0 1 0; 0 0 1];

%Pad zeros on all the sides

C=padarray(A,[1 1]);

%Intialize a matrix of matrix size A with zeros

D=false(size(A));

for i=1:size(C,1)-2

    for j=1:size(C,2)-2

        %Perform logical AND operation

        D(i,j)=sum(sum(B&C(i:i+2,j:j+2)));

    end

end

display(D);

Example 2:

A=imread('text.png');

Original Image

A=im2bw(A);
%structuring element

B=[1;1;1;1;1;1;1;];

C=padarray(A,[3 0]);

D=false(size(A));

for i=1:size(C,1)-6

    for j=1:size(C,2)

        D(i,j)=sum(B&C(i:i+6,j));

    end

end

figure,imshow(D);

Dilated Image

Example 3:

A=imread('text.png');

A=im2bw(A);
%Structuring element

B=[1 1 1 1 1 1 1;];
C=padarray(A,[0 3]);

D=false(size(A));

for i=1:size(C,1)

    for j=1:size(C,2)-6

        D(i,j)=sum(B&C(i,j:j+6));

    end

end

figure,imshow(D);

Dilated image