Kamel Ghanem Ghalem if you mean reduce the size of the image without using imresize command:

I = imread('lena.png'); % Replace 'lena.png' with the path to your image file

% Convert to grayscale if it's a color image

if size(I, 3) == 30

I = rgb2gray(I);

end

% sampling the image by a factor of 0.5

samp=(1:2:end, 1:2:end);

% Display the original and downsampled images

subplot(2, 1, 1);

imshow(I);

title('Original Image');

subplot(2, 1, 2);

imshow(samp);

title('Downsampled Image');

Use loop for.

Kamel Ghanem Ghalem Just for quick processing, otherwise you can try this one without transverse RGB to Grayscale

img = imread('lena.png'); % Get the size of the original image

[rows, cols, ~] = size(img); % Calculate the new size

new_rows = floor(rows * 0.5);

new_cols = floor(cols * 0.5); subsampled_img = img(1:2:end, 1:2:end, :); % Display the subsampled image

figure;

imshow(img);

title('Original Image'); figure; imshow(subsampled_img); title('Subsampled Image (0.5 factor)');