Stacking elements of RGB array in a single array

Hello,

i want to read all the elements of 1st coloumn of 'r','g' and 'b' into a single array. i need it to look like how 'col1' looks.

    i = imread ('img.png');
    r = i(:,:,1);
    g = i(:,:,2);
    b = i(:,:,3);
    col1 = [r(1,1) g(1,1) b(1,1); r(1,2) g(1,2) b(1,2); r(1,3) g(1,3) b(1,3)];