I have created an algorithm for a median RGB image filter, however, it doesn't seem to be working.

clc

I =imread('phonebox2_noisy.bmp');

I = double(I);

[row, col, dim]=size(w);

red= I(:,:,1);

green= I(:,:,2);

blue= I(:,:,3);

for i = 2:1:row-1

for j = 2:1:col-1

red_f(i,j)=w(1,1)*red(i-1,j-1)+w(1,2)*red(i-1,j)+w(1,3)*red(i-1,j+1)+w(2,1)*red(i,j-1)+w(2,2)*red(i,j)+w(2,3)*red(i,j+1)+...

w(3,1)*red(i+1,j-1)+w(3,2)*red(i+1,j)+w(3,3)*red(i+1,j+1);

red_f=sort(red_f);

I(i,j)= red_f(5);

green_f(i,j)= w(1,1)*green(i-1,j-1)+w(1,2)*green(i-1,j)+w(1,3)*green(i-1,j+1)+w(2,1)*green(i,j-1)+w(2,2)*green(i,j)+w(2,3)*green(i,j+1)+...

w(3,1)*green(i+1,j-1)+w(3,2)*green(i+1,j)+w(3,3)*green(i+1,j+1);

green_f=sort(green_f);

I(i,j)= green_f(5);

blue_f(i,j)=w(1,1)*blue(i-1,j-1)+w(1,2)*blue(i-1,j)+w(1,3)*blue(i-1,j+1)+w(2,1)*blue(i,j-1)+w(2,2)*blue(i,j)+w(2,3)*blue(i,j+1)+...

w(3,1)*blue(i+1,j-1)+w(3,2)*blue(i+1,j)+w(3,3)*blue(i+1,j+1);

blue_f=sort(blue_f);

I(i,j)= blue_f(5);

end

end

final=cat(3,red_f,green_f,blue_f);

figure;

imshow(uint(w));

title('phonebox noisy');

figure;

imshow(uint8(final));

title('phonebox');

Answer 1

[DGM]

I don't know why you're using a weighting array that doesn't exist, but since you say this is a median filter, I'm going to assume you want a plain median filter.

I = imread('peppers.png'); % i don't have your image
I = imnoise(I,'salt & pepper');

[row, col, channels] = size(I); % dim() is a function
[red green blue] = imsplit(I);

output = zeros(size(I),class(I));
for i = 2:1:row-1
    for j = 2:1:col-1
        % if you want to do a median, i don't know why you're using a weighting filter
        red_f = red(i-1:i+1,j-1:j+1);
        red_f = sort(red_f(:));
        output(i,j,1) = red_f(5); % you need to actually write to the output array
        
        % of course, you can just use median() instead.
        output(i,j,2) = median(green(i-1:i+1,j-1:j+1),'all');
        output(i,j,3) = median(blue(i-1:i+1,j-1:j+1),'all');
        
        % or you can just use a third loop
    end
end

imshow(I);
title('phonebox noisy');

figure;
imshow(output);
title('phonebox');

[Lewis Laurence]

thank you for your help. I'm very new to matlab

[Lewis Laurence]

how would I use this for a 5 by 5 matrix

[DGM]

This would be a start. This pulls the filter size out as a parameter

I = imread('peppers.png'); % i don't have your image
I = imnoise(I,'salt & pepper');

fs = [5 5];

[rows, cols, channels] = size(I);
pw = floor(fs/2);
output = I;
for rr = 1+pw(1):1:rows-pw(1)
    for cc = 1+pw(2):1:cols-pw(2)
        sample = I(rr-pw(1):rr+pw(1),cc-pw(2):cc+pw(2),:);
        for c = 1:channels
            output(rr,cc,c) = median(sample(:,:,c),'all');
        end
    end
end

imshow(output)

Note that the approach you were using avoids indexing outside the array boundaries by restricting the region over which the filter actually processes the image. Normally, I'd do this by padding the image instead. This is another example that uses padding, but isn't adapted for multichannel images:

https://www.mathworks.com/matlabcentral/answers/1466576-changing-a-3x3-to-5x5-median-filter