MATLAB – Image Edge Detection using Prewitt Operator from Scratch

Q: What is MATLAB – Image Edge Detection using Prewitt Operator from Scratch?

In this article, we will learn MATLAB – Image Edge Detection using Prewitt Operator from Scratch,This free MATLAB tutorial for complete beginners will help you learn MATLAB from scratch.

MATLAB - Image Edge Detection using Robert Operator from Scratch

Prewitt Operator:

Approach: Step 1: Input – Read an image Step 2: Convert the true-color RGB image to the grayscale image Step 3: Convert the image to double Step 4: Pre-allocate the filtered_image matrix with zeros Step 5: Define Prewitt Operator Mask Step 6: Edge Detection Process (Compute Gradient approximation and magnitude of vector) Step 7: Display the filtered image Step 8: Thresholding on the filtered image Step 9: Display the edge-detected image

Implementation in MATLAB:

% MATLAB Code | Prewitt 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)); 
  
% Prewitt Operator Mask 
Mx = [-1 0 1; -1 0 1; -1 0 1]; 
My = [-1 -1 -1; 0 0 0; 1 1 1]; 
  
% Edge Detection Process 
% When i = 1 and j = 1, then filtered_image pixel   
% position will be filtered_image(2, 2) 
% The mask is of 3x3, so we need to traverse  
% to filtered_image(size(input_image, 1) - 2 
%, size(input_image, 2) - 2) 
% Thus we are not considering the borders. 
for i = 1:size(input_image, 1) - 2 
    for j = 1:size(input_image, 2) - 2 
  
        % Gradient approximations 
        Gx = sum(sum(Mx.*input_image(i:i+2, j:j+2))); 
        Gy = sum(sum(My.*input_image(i:i+2, j:j+2))); 
                 
        % Calculate magnitude of vector 
        filtered_image(i+1, j+1) = 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'); 