how can i divide image (grayscale) into overlapping blocks 8*8 ??

how can i divide image (grayscale) into overlapping blocks 8*8 ??

Answer 1

[Abhipsa]

Hi @Amina BENKESSIRAT,

To divide a grayscale image into overlapping 8x8 blocks in MATLAB R2024b, nested loops can be used to iterate over the image and extract the blocks.

The following code snippet demonstrates this:

% Read the image
img = imread('sample.jpg'); 
if size(img, 3) == 3
    img = rgb2gray(img); % convert the image to grayscale if it's RGB 
end

% Define block size and overlap
blockSize = 8;
overlap = 4; % it can be calculated based on the percentage of overlapping needed
%in the above case, 50% overlapping is considered

% get image dimensions
[img_height, img_width] = size(img);

% Calculate the step size which will determine how much to move the window each time
stepSize = blockSize - overlap;

% initialize a cell array to store the blocks
blocks = {};

blkIdx = 1; %index of the current extracted block

% loop over the image to extract blocks
for row = 1:stepSize:img_height-blockSize+1
    for col = 1:stepSize:img_width-blockSize+1
        % extract the current block(even partial blocks at the edges have been added)
        block = img(row:min(row+blockSize-1, img_height), ...
                    col:min(col+blockSize-1, img_width));
        
        % store the extracted block in the cell array at blkIdx
        blocks{blkIdx} = block;
        blkIdx = blkIdx + 1;
    end
end

% display the number of blocks extracted
fprintf('Extracted %d blocks.\n', blkIdx-1);

Extracted 1039680 blocks.

% Display some of the extracted blocks
figure;
for k = 1:min(9, blkIdx-1)  % Display the first 9 blocks or fewer
    subplot(3, 3, k);
    imshow(blocks{k});
    title(['Block ' num2str(k)]);
end

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You can refer to the following MATLAB documentations for more details:

• imread: https://www.mathworks.com/help/releases/R2024b/matlab/ref/imread.html
• rgb2gray: https://www.mathworks.com/help/releases/R2024b/matlab/ref/rgb2gray.html

I hope this helps.