Max filter for 5 x 5 and 9 x 9 pixel size

%READ AN IMAGE
A = imread('sample2.jpg');
A = rgb2gray(A(1:300,1:300,:));

figure,imshow(A),title('ORIGINAL IMAGE');

%PREALLOCATE THE OUTPUT MATRIX
B=zeros(size(A));

%PAD THE MATRIX A WITH ZEROS
modifyA=padarray(A,[1 1]);

      x=[1:3]';
      y=[1:3]';

      for i= 1:size(modifyA,1)-2
          for j=1:size(modifyA,2)-2

              %VECTORIZED METHOD
              window=reshape(modifyA(i+x-1,j+y-1),[],1);

               %FIND THE MAXIMUM VALUE IN THE SELECTED WINDOW
              B(i,j)=max(window);
          end
      end

%CONVERT THE OUTPUT MATRIX TO 0-255 RANGE IMAGE TYPE
B=uint8(B);
figure,imshow(B),title('IMAGE AFTER MAX FILTERING');

I want to do a 5x5 and 9x9 size pixel fro this coding. Can someone help me ?

Thank you

Answer 1

[Walter Roberson]

For the N x N, use

x = (1:N).';
y = x;

[Jensen]

Is it that i only need to change

x=[1:3]'; y=[1:3]';

into x = (1:N).'; y = x; ??

[Jensen]

When i change it. The coding got error :

      |??? Index exceeds matrix dimensions.

      Error in ==> Untitled at 20
                  window=reshape(modifyA(i+x-1,j+y-1),[],1);|

[Walter Roberson]

The code has size(modifyA,1)-2 in the for loop. Change that -2 to -N+1 where N is a variable holding the desired size. Make the same kind of change on the following line.

Answer 2

[Andrei Bobrov]

In your case use function imdilate from Image Processing Toolbox,

for 5x5:

B = imdilate(A,ones(5));

for 9x9:

B = imdilate(A,ones(9));

[Jensen]

I am kinda new in this Matlab coding. Can u teach how to use imdilate from Image Prcessing Toolbox ? Is it i just at it onto the code ?

[Andrei Bobrov]

You must be install Image Processing Toolbox (if it is not installed) and run following:

A = imread('sample2.jpg');
A = rgb2gray(A(1:300,1:300,:));
figure,imshow(A),title('ORIGINAL IMAGE');
B = imdilate(A,ones(5));
B=uint8(B);
figure,imshow(B),title('IMAGE AFTER MAX FILTERING');

[Image Analyst]

It looks like it may be a homework assignment since I just answered this yesterday for someone else: http://www.mathworks.com/matlabcentral/answers/121748#answer_128654