How to find the positions of pixels with 4 neighborhood in a binary pixel grid

Hi @Harrison,

Glad to help. You asked, “Do you know how to get it to display the coordinate locations of pixels that are 4-neighbors? in your example it would just return (i,j) for each pixel labeled 2. “

To achieve the desired functionality of displaying the coordinate locations of pixels that are labeled as 4-neighbors, you will need to make a few modifications to the existing MATLAB code. The primary goal is to store the coordinates of the pixels that are updated to the value of fourneighbors (which is set to 2 in this case) and then display these coordinates after processing the image matrix. Here is a step-by-step breakdown of the modifications:

Initialize a List for Coordinates: create an array to store the coordinates of the pixels that are updated.

Update the Logic to Store Coordinates: Whenever a pixel is updated to the value of fourneighbors, you will also store its coordinates in the list.

Display the Coordinates: After processing the entire image matrix, display the collected coordinates.

Here is the revised version of your MATLAB code that incorporates these changes:

% Initialize a sample 3x3 image matrix
image = [1 0 1; 
       1 1 1; 
       0 1 0];

% Initialize the value to assign to neighboring pixels
fourneighbors = 2; % Example value to represent neighboring 
pixels

% Initialize an array to hold the coordinates of updated pixels
updatedCoordinates = []; 

% Loop through the 3x3 grid
for i = 1:3
  for j = 1:3
      % Check the upper neighbor
      if i > 1 && image(i-1,j) == 1 && image(i,j) == 1
          image(i,j) = fourneighbors;    
          updatedCoordinates = [updatedCoordinates; i, j]; % 
          Store coordinates
      end
      % Check the left neighbor
      if j > 1 && image(i,j-1) == 1 && image(i,j) == 1
          image(i,j) = fourneighbors;
          updatedCoordinates = [updatedCoordinates; i, j]; % 
          Store coordinates
      end
      % Check the lower neighbor
      if i < 3 && image(i+1,j) == 1 && image(i,j) == 1 
          image(i,j) = fourneighbors;
          updatedCoordinates = [updatedCoordinates; i, j]; % 
          Store coordinates
      end
      % Check the right neighbor
      if j < 3 && image(i,j+1) == 1 && image(i,j) == 1
          image(i,j) = fourneighbors;
          updatedCoordinates = [updatedCoordinates; i, j]; % 
          Store coordinates
      end
  end
end

% Display the final image matrix
disp('Updated Image Matrix:');
disp(image);

% Display the coordinates of pixels labeled as 4-neighbors
disp('Coordinates of 4-neighbors (labeled as 2):');
disp(updatedCoordinates);

Please see attached.

In the above modified code snippet, the variable updatedCoordinates is initialized as an empty array. Each time a pixel is updated to fourneighbors, its coordinates (i, j) are appended to this array. After the loops, use disp to show the updated image matrix and the coordinates of the pixels that were updated.

This updated code will now not only modify the pixel values based on their neighbors but also provide a clear output of the coordinates of the pixels that have been labeled as 4-neighbors. You can run this code in your MATLAB environment, and it should function as intended.

If you have any further questions or require additional modifications, please feel free to ask!