I want create a convolution filter for RGB images

Hello,

I want create a 2-D convolution filter. I know there are some functions like imfilter etc. but i don't want use them. How can i change the code on the below for images ?

%INPUT  MATRIX
A = zeros(5);
A(:) = 1:25;

%KERNEL
avg3 = ones(3)/9;

%PAD THE MATRIX WITH ZEROS
B = padarray(A,[1 1]);
% PRE-ALLOCATE THE MATRIX
Output = zeros([size(A,1) size(A,2)]);

%PERFORM COONVOLUTION
for i = 1:size(B,1)-2
    for j = 1:size(B,2)-2
        Temp = B(i:i+2,j:j+2).*avg3;
        Output(i,j) = sum(Temp(:));
    end
 end

display(Output);

[Rik]

It already looks like it should work for 2D arrays. Do you want it to work on RGB images?

[Mustafa Uysal]

Yes i want it to work on RGB images.

[Guillaume]

"but i don't want use them"

Why not? What is the point of reinventing the wheel? The built-in functions will perform a lot faster and more reliably than what you have written.

What you have written by the way is not a convolution. It works like a convolution because your convolution matrix is symmetrical but it is a correlation.

With regards to your question, what's stopping you from performing the same calculation on all 3 planes, in successsion?

Finally, note that

Output = zeros([size(A,1) size(A,2)]);

is simply

Output = zeros(size(A));

The latter has the advantage of also working straight out of the box for colour images.