Implement a nonlinear filter — a median filter.

Implement a nonlinear filter — a median filter. While the Gaussian filter works by computing locally-weighted values of the signal, the median filter first sorts the signal values within a window and then takes the middle value (i.e., the median). Implement a function, simpleMedian, which takes as input an image, I, and the dimensions of the median filter, W and H, and returns a median filtered image. Zero-pad the image within the function to ensure that the filtered image is the same size as the original image. Apply a 12×12 median filter to the loaded images. Show the results.

CODE:

% load the input image
img = imread('Old_house.jpg');

% apply a 12x12 median filter to the image
filtered_img = simpleMedian(img, 12, 12);

% display the input and filtered images side by side
figure;
subplot(1,2,1);
imshow(img);
title('Input Image');
subplot(1,2,2);
imshow(filtered_img);
title('Filtered Image');

function filtered_img = simpleMedian(I, W, H)
% zero-pad the image
padded_img = padarray(I, [(H-1)/2 (W-1)/2], 'symmetric');

% initialize the filtered image
filtered_img = zeros(size(I), 'like', I);

% loop through each pixel in the image
for i = 1:size(I,1)
    for j = 1:size(I,2)
        % extract the window centered at (i,j)
        window = padded_img(i:i+H-1, j:j+W-1);
        
        % take the median of the window
        filtered_img(i,j) = median(window(:));
    end
end
end

ERROR:

Error using padarray

Expected input number 2, PADSIZE, to be integer-valued.

Error in padarray>ParseInputs (line 108)

validateattributes(padSize, {'double'}, {'real' 'vector' 'nonnan'

'nonnegative' ...

Error in padarray (line 75)

[a, method, padSize, padVal, direction, catConverter] =

ParseInputs(args{:});

Error in untitled1_12>simpleMedian (line 18)

padded_img = padarray(I, [(H-1)/2 (W-1)/2], 'symmetric');

Error in untitled1_12 (line 5)

filtered_img = simpleMedian(img, 12, 12);

Answer 1

[Walter Roberson]

padded_img = padarray(I, [(H-1)/2 (W-1)/2], 'symmetric');

Suppose the height, H, is even, such as if H = 12. Then H-1 is 11, and 11/2 is not an integer. So you are asking to pad by 5 1/2 rows and columns on each side, which is not something that is permitted.