MATLAB - Image Edge Detection using Robert Operator from Scratch

% MATLAB Code | Robert Operator from Scratch

% Read Input Image
input_image = imread('[name of input image file].[file format]');

% Displaying Input Image
input_image = uint8(input_image);
figure, imshow(input_image); title('Input Image');

% Convert the truecolor RGB image to the grayscale image
input_image = rgb2gray(input_image);

% Convert the image to double
input_image = double(input_image);

% Pre-allocate the filtered_image matrix with zeros
filtered_image = zeros(size(input_image));

% Robert Operator Mask
Mx = [1 0; 0 -1];
My = [0 1; -1 0];

% Edge Detection Process
% When i = 1 and j = 1, then filtered_image pixel  
% position will be filtered_image(1, 1)
% The mask is of 2x2, so we need to traverse 
% to filtered_image(size(input_image, 1) - 1
%, size(input_image, 2) - 1)
for i = 1:size(input_image, 1) - 1
    for j = 1:size(input_image, 2) - 1

        % Gradient approximations
        Gx = sum(sum(Mx.*input_image(i:i+1, j:j+1)));
        Gy = sum(sum(My.*input_image(i:i+1, j:j+1)));
               
        % Calculate magnitude of vector
        filtered_image(i, j) = sqrt(Gx.^2 + Gy.^2);
       
    end
end

% Displaying Filtered Image
filtered_image = uint8(filtered_image);
figure, imshow(filtered_image); title('Filtered Image');

% Define a threshold value
thresholdValue = 100; % varies between [0 255]
output_image = max(filtered_image, thresholdValue);
output_image(output_image == round(thresholdValue)) = 0;

% Displaying Output Image
output_image = im2bw(output_image);
figure, imshow(output_image); title('Edge Detected Image');